The Design and Implementation of the FreeBSD Operating System, Second Edition
Now available: The Design and Implementation of the FreeBSD Operating System (Second Edition)


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FreeBSD/Linux Kernel Cross Reference
sys/mm/huge_memory.c

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    1 /*
    2  *  Copyright (C) 2009  Red Hat, Inc.
    3  *
    4  *  This work is licensed under the terms of the GNU GPL, version 2. See
    5  *  the COPYING file in the top-level directory.
    6  */
    7 
    8 #include <linux/mm.h>
    9 #include <linux/sched.h>
   10 #include <linux/highmem.h>
   11 #include <linux/hugetlb.h>
   12 #include <linux/mmu_notifier.h>
   13 #include <linux/rmap.h>
   14 #include <linux/swap.h>
   15 #include <linux/shrinker.h>
   16 #include <linux/mm_inline.h>
   17 #include <linux/kthread.h>
   18 #include <linux/khugepaged.h>
   19 #include <linux/freezer.h>
   20 #include <linux/mman.h>
   21 #include <linux/pagemap.h>
   22 #include <linux/migrate.h>
   23 
   24 #include <asm/tlb.h>
   25 #include <asm/pgalloc.h>
   26 #include "internal.h"
   27 
   28 /*
   29  * By default transparent hugepage support is enabled for all mappings
   30  * and khugepaged scans all mappings. Defrag is only invoked by
   31  * khugepaged hugepage allocations and by page faults inside
   32  * MADV_HUGEPAGE regions to avoid the risk of slowing down short lived
   33  * allocations.
   34  */
   35 unsigned long transparent_hugepage_flags __read_mostly =
   36 #ifdef CONFIG_TRANSPARENT_HUGEPAGE_ALWAYS
   37         (1<<TRANSPARENT_HUGEPAGE_FLAG)|
   38 #endif
   39 #ifdef CONFIG_TRANSPARENT_HUGEPAGE_MADVISE
   40         (1<<TRANSPARENT_HUGEPAGE_REQ_MADV_FLAG)|
   41 #endif
   42         (1<<TRANSPARENT_HUGEPAGE_DEFRAG_FLAG)|
   43         (1<<TRANSPARENT_HUGEPAGE_DEFRAG_KHUGEPAGED_FLAG)|
   44         (1<<TRANSPARENT_HUGEPAGE_USE_ZERO_PAGE_FLAG);
   45 
   46 /* default scan 8*512 pte (or vmas) every 30 second */
   47 static unsigned int khugepaged_pages_to_scan __read_mostly = HPAGE_PMD_NR*8;
   48 static unsigned int khugepaged_pages_collapsed;
   49 static unsigned int khugepaged_full_scans;
   50 static unsigned int khugepaged_scan_sleep_millisecs __read_mostly = 10000;
   51 /* during fragmentation poll the hugepage allocator once every minute */
   52 static unsigned int khugepaged_alloc_sleep_millisecs __read_mostly = 60000;
   53 static struct task_struct *khugepaged_thread __read_mostly;
   54 static DEFINE_MUTEX(khugepaged_mutex);
   55 static DEFINE_SPINLOCK(khugepaged_mm_lock);
   56 static DECLARE_WAIT_QUEUE_HEAD(khugepaged_wait);
   57 /*
   58  * default collapse hugepages if there is at least one pte mapped like
   59  * it would have happened if the vma was large enough during page
   60  * fault.
   61  */
   62 static unsigned int khugepaged_max_ptes_none __read_mostly = HPAGE_PMD_NR-1;
   63 
   64 static int khugepaged(void *none);
   65 static int mm_slots_hash_init(void);
   66 static int khugepaged_slab_init(void);
   67 static void khugepaged_slab_free(void);
   68 
   69 #define MM_SLOTS_HASH_HEADS 1024
   70 static struct hlist_head *mm_slots_hash __read_mostly;
   71 static struct kmem_cache *mm_slot_cache __read_mostly;
   72 
   73 /**
   74  * struct mm_slot - hash lookup from mm to mm_slot
   75  * @hash: hash collision list
   76  * @mm_node: khugepaged scan list headed in khugepaged_scan.mm_head
   77  * @mm: the mm that this information is valid for
   78  */
   79 struct mm_slot {
   80         struct hlist_node hash;
   81         struct list_head mm_node;
   82         struct mm_struct *mm;
   83 };
   84 
   85 /**
   86  * struct khugepaged_scan - cursor for scanning
   87  * @mm_head: the head of the mm list to scan
   88  * @mm_slot: the current mm_slot we are scanning
   89  * @address: the next address inside that to be scanned
   90  *
   91  * There is only the one khugepaged_scan instance of this cursor structure.
   92  */
   93 struct khugepaged_scan {
   94         struct list_head mm_head;
   95         struct mm_slot *mm_slot;
   96         unsigned long address;
   97 };
   98 static struct khugepaged_scan khugepaged_scan = {
   99         .mm_head = LIST_HEAD_INIT(khugepaged_scan.mm_head),
  100 };
  101 
  102 
  103 static int set_recommended_min_free_kbytes(void)
  104 {
  105         struct zone *zone;
  106         int nr_zones = 0;
  107         unsigned long recommended_min;
  108         extern int min_free_kbytes;
  109 
  110         if (!khugepaged_enabled())
  111                 return 0;
  112 
  113         for_each_populated_zone(zone)
  114                 nr_zones++;
  115 
  116         /* Make sure at least 2 hugepages are free for MIGRATE_RESERVE */
  117         recommended_min = pageblock_nr_pages * nr_zones * 2;
  118 
  119         /*
  120          * Make sure that on average at least two pageblocks are almost free
  121          * of another type, one for a migratetype to fall back to and a
  122          * second to avoid subsequent fallbacks of other types There are 3
  123          * MIGRATE_TYPES we care about.
  124          */
  125         recommended_min += pageblock_nr_pages * nr_zones *
  126                            MIGRATE_PCPTYPES * MIGRATE_PCPTYPES;
  127 
  128         /* don't ever allow to reserve more than 5% of the lowmem */
  129         recommended_min = min(recommended_min,
  130                               (unsigned long) nr_free_buffer_pages() / 20);
  131         recommended_min <<= (PAGE_SHIFT-10);
  132 
  133         if (recommended_min > min_free_kbytes)
  134                 min_free_kbytes = recommended_min;
  135         setup_per_zone_wmarks();
  136         return 0;
  137 }
  138 late_initcall(set_recommended_min_free_kbytes);
  139 
  140 static int start_khugepaged(void)
  141 {
  142         int err = 0;
  143         if (khugepaged_enabled()) {
  144                 if (!khugepaged_thread)
  145                         khugepaged_thread = kthread_run(khugepaged, NULL,
  146                                                         "khugepaged");
  147                 if (unlikely(IS_ERR(khugepaged_thread))) {
  148                         printk(KERN_ERR
  149                                "khugepaged: kthread_run(khugepaged) failed\n");
  150                         err = PTR_ERR(khugepaged_thread);
  151                         khugepaged_thread = NULL;
  152                 }
  153 
  154                 if (!list_empty(&khugepaged_scan.mm_head))
  155                         wake_up_interruptible(&khugepaged_wait);
  156 
  157                 set_recommended_min_free_kbytes();
  158         } else if (khugepaged_thread) {
  159                 kthread_stop(khugepaged_thread);
  160                 khugepaged_thread = NULL;
  161         }
  162 
  163         return err;
  164 }
  165 
  166 static atomic_t huge_zero_refcount;
  167 static unsigned long huge_zero_pfn __read_mostly;
  168 
  169 static inline bool is_huge_zero_pfn(unsigned long pfn)
  170 {
  171         unsigned long zero_pfn = ACCESS_ONCE(huge_zero_pfn);
  172         return zero_pfn && pfn == zero_pfn;
  173 }
  174 
  175 static inline bool is_huge_zero_pmd(pmd_t pmd)
  176 {
  177         return is_huge_zero_pfn(pmd_pfn(pmd));
  178 }
  179 
  180 static unsigned long get_huge_zero_page(void)
  181 {
  182         struct page *zero_page;
  183 retry:
  184         if (likely(atomic_inc_not_zero(&huge_zero_refcount)))
  185                 return ACCESS_ONCE(huge_zero_pfn);
  186 
  187         zero_page = alloc_pages((GFP_TRANSHUGE | __GFP_ZERO) & ~__GFP_MOVABLE,
  188                         HPAGE_PMD_ORDER);
  189         if (!zero_page) {
  190                 count_vm_event(THP_ZERO_PAGE_ALLOC_FAILED);
  191                 return 0;
  192         }
  193         count_vm_event(THP_ZERO_PAGE_ALLOC);
  194         preempt_disable();
  195         if (cmpxchg(&huge_zero_pfn, 0, page_to_pfn(zero_page))) {
  196                 preempt_enable();
  197                 __free_page(zero_page);
  198                 goto retry;
  199         }
  200 
  201         /* We take additional reference here. It will be put back by shrinker */
  202         atomic_set(&huge_zero_refcount, 2);
  203         preempt_enable();
  204         return ACCESS_ONCE(huge_zero_pfn);
  205 }
  206 
  207 static void put_huge_zero_page(void)
  208 {
  209         /*
  210          * Counter should never go to zero here. Only shrinker can put
  211          * last reference.
  212          */
  213         BUG_ON(atomic_dec_and_test(&huge_zero_refcount));
  214 }
  215 
  216 static int shrink_huge_zero_page(struct shrinker *shrink,
  217                 struct shrink_control *sc)
  218 {
  219         if (!sc->nr_to_scan)
  220                 /* we can free zero page only if last reference remains */
  221                 return atomic_read(&huge_zero_refcount) == 1 ? HPAGE_PMD_NR : 0;
  222 
  223         if (atomic_cmpxchg(&huge_zero_refcount, 1, 0) == 1) {
  224                 unsigned long zero_pfn = xchg(&huge_zero_pfn, 0);
  225                 BUG_ON(zero_pfn == 0);
  226                 __free_page(__pfn_to_page(zero_pfn));
  227         }
  228 
  229         return 0;
  230 }
  231 
  232 static struct shrinker huge_zero_page_shrinker = {
  233         .shrink = shrink_huge_zero_page,
  234         .seeks = DEFAULT_SEEKS,
  235 };
  236 
  237 #ifdef CONFIG_SYSFS
  238 
  239 static ssize_t double_flag_show(struct kobject *kobj,
  240                                 struct kobj_attribute *attr, char *buf,
  241                                 enum transparent_hugepage_flag enabled,
  242                                 enum transparent_hugepage_flag req_madv)
  243 {
  244         if (test_bit(enabled, &transparent_hugepage_flags)) {
  245                 VM_BUG_ON(test_bit(req_madv, &transparent_hugepage_flags));
  246                 return sprintf(buf, "[always] madvise never\n");
  247         } else if (test_bit(req_madv, &transparent_hugepage_flags))
  248                 return sprintf(buf, "always [madvise] never\n");
  249         else
  250                 return sprintf(buf, "always madvise [never]\n");
  251 }
  252 static ssize_t double_flag_store(struct kobject *kobj,
  253                                  struct kobj_attribute *attr,
  254                                  const char *buf, size_t count,
  255                                  enum transparent_hugepage_flag enabled,
  256                                  enum transparent_hugepage_flag req_madv)
  257 {
  258         if (!memcmp("always", buf,
  259                     min(sizeof("always")-1, count))) {
  260                 set_bit(enabled, &transparent_hugepage_flags);
  261                 clear_bit(req_madv, &transparent_hugepage_flags);
  262         } else if (!memcmp("madvise", buf,
  263                            min(sizeof("madvise")-1, count))) {
  264                 clear_bit(enabled, &transparent_hugepage_flags);
  265                 set_bit(req_madv, &transparent_hugepage_flags);
  266         } else if (!memcmp("never", buf,
  267                            min(sizeof("never")-1, count))) {
  268                 clear_bit(enabled, &transparent_hugepage_flags);
  269                 clear_bit(req_madv, &transparent_hugepage_flags);
  270         } else
  271                 return -EINVAL;
  272 
  273         return count;
  274 }
  275 
  276 static ssize_t enabled_show(struct kobject *kobj,
  277                             struct kobj_attribute *attr, char *buf)
  278 {
  279         return double_flag_show(kobj, attr, buf,
  280                                 TRANSPARENT_HUGEPAGE_FLAG,
  281                                 TRANSPARENT_HUGEPAGE_REQ_MADV_FLAG);
  282 }
  283 static ssize_t enabled_store(struct kobject *kobj,
  284                              struct kobj_attribute *attr,
  285                              const char *buf, size_t count)
  286 {
  287         ssize_t ret;
  288 
  289         ret = double_flag_store(kobj, attr, buf, count,
  290                                 TRANSPARENT_HUGEPAGE_FLAG,
  291                                 TRANSPARENT_HUGEPAGE_REQ_MADV_FLAG);
  292 
  293         if (ret > 0) {
  294                 int err;
  295 
  296                 mutex_lock(&khugepaged_mutex);
  297                 err = start_khugepaged();
  298                 mutex_unlock(&khugepaged_mutex);
  299 
  300                 if (err)
  301                         ret = err;
  302         }
  303 
  304         return ret;
  305 }
  306 static struct kobj_attribute enabled_attr =
  307         __ATTR(enabled, 0644, enabled_show, enabled_store);
  308 
  309 static ssize_t single_flag_show(struct kobject *kobj,
  310                                 struct kobj_attribute *attr, char *buf,
  311                                 enum transparent_hugepage_flag flag)
  312 {
  313         return sprintf(buf, "%d\n",
  314                        !!test_bit(flag, &transparent_hugepage_flags));
  315 }
  316 
  317 static ssize_t single_flag_store(struct kobject *kobj,
  318                                  struct kobj_attribute *attr,
  319                                  const char *buf, size_t count,
  320                                  enum transparent_hugepage_flag flag)
  321 {
  322         unsigned long value;
  323         int ret;
  324 
  325         ret = kstrtoul(buf, 10, &value);
  326         if (ret < 0)
  327                 return ret;
  328         if (value > 1)
  329                 return -EINVAL;
  330 
  331         if (value)
  332                 set_bit(flag, &transparent_hugepage_flags);
  333         else
  334                 clear_bit(flag, &transparent_hugepage_flags);
  335 
  336         return count;
  337 }
  338 
  339 /*
  340  * Currently defrag only disables __GFP_NOWAIT for allocation. A blind
  341  * __GFP_REPEAT is too aggressive, it's never worth swapping tons of
  342  * memory just to allocate one more hugepage.
  343  */
  344 static ssize_t defrag_show(struct kobject *kobj,
  345                            struct kobj_attribute *attr, char *buf)
  346 {
  347         return double_flag_show(kobj, attr, buf,
  348                                 TRANSPARENT_HUGEPAGE_DEFRAG_FLAG,
  349                                 TRANSPARENT_HUGEPAGE_DEFRAG_REQ_MADV_FLAG);
  350 }
  351 static ssize_t defrag_store(struct kobject *kobj,
  352                             struct kobj_attribute *attr,
  353                             const char *buf, size_t count)
  354 {
  355         return double_flag_store(kobj, attr, buf, count,
  356                                  TRANSPARENT_HUGEPAGE_DEFRAG_FLAG,
  357                                  TRANSPARENT_HUGEPAGE_DEFRAG_REQ_MADV_FLAG);
  358 }
  359 static struct kobj_attribute defrag_attr =
  360         __ATTR(defrag, 0644, defrag_show, defrag_store);
  361 
  362 static ssize_t use_zero_page_show(struct kobject *kobj,
  363                 struct kobj_attribute *attr, char *buf)
  364 {
  365         return single_flag_show(kobj, attr, buf,
  366                                 TRANSPARENT_HUGEPAGE_USE_ZERO_PAGE_FLAG);
  367 }
  368 static ssize_t use_zero_page_store(struct kobject *kobj,
  369                 struct kobj_attribute *attr, const char *buf, size_t count)
  370 {
  371         return single_flag_store(kobj, attr, buf, count,
  372                                  TRANSPARENT_HUGEPAGE_USE_ZERO_PAGE_FLAG);
  373 }
  374 static struct kobj_attribute use_zero_page_attr =
  375         __ATTR(use_zero_page, 0644, use_zero_page_show, use_zero_page_store);
  376 #ifdef CONFIG_DEBUG_VM
  377 static ssize_t debug_cow_show(struct kobject *kobj,
  378                                 struct kobj_attribute *attr, char *buf)
  379 {
  380         return single_flag_show(kobj, attr, buf,
  381                                 TRANSPARENT_HUGEPAGE_DEBUG_COW_FLAG);
  382 }
  383 static ssize_t debug_cow_store(struct kobject *kobj,
  384                                struct kobj_attribute *attr,
  385                                const char *buf, size_t count)
  386 {
  387         return single_flag_store(kobj, attr, buf, count,
  388                                  TRANSPARENT_HUGEPAGE_DEBUG_COW_FLAG);
  389 }
  390 static struct kobj_attribute debug_cow_attr =
  391         __ATTR(debug_cow, 0644, debug_cow_show, debug_cow_store);
  392 #endif /* CONFIG_DEBUG_VM */
  393 
  394 static struct attribute *hugepage_attr[] = {
  395         &enabled_attr.attr,
  396         &defrag_attr.attr,
  397         &use_zero_page_attr.attr,
  398 #ifdef CONFIG_DEBUG_VM
  399         &debug_cow_attr.attr,
  400 #endif
  401         NULL,
  402 };
  403 
  404 static struct attribute_group hugepage_attr_group = {
  405         .attrs = hugepage_attr,
  406 };
  407 
  408 static ssize_t scan_sleep_millisecs_show(struct kobject *kobj,
  409                                          struct kobj_attribute *attr,
  410                                          char *buf)
  411 {
  412         return sprintf(buf, "%u\n", khugepaged_scan_sleep_millisecs);
  413 }
  414 
  415 static ssize_t scan_sleep_millisecs_store(struct kobject *kobj,
  416                                           struct kobj_attribute *attr,
  417                                           const char *buf, size_t count)
  418 {
  419         unsigned long msecs;
  420         int err;
  421 
  422         err = strict_strtoul(buf, 10, &msecs);
  423         if (err || msecs > UINT_MAX)
  424                 return -EINVAL;
  425 
  426         khugepaged_scan_sleep_millisecs = msecs;
  427         wake_up_interruptible(&khugepaged_wait);
  428 
  429         return count;
  430 }
  431 static struct kobj_attribute scan_sleep_millisecs_attr =
  432         __ATTR(scan_sleep_millisecs, 0644, scan_sleep_millisecs_show,
  433                scan_sleep_millisecs_store);
  434 
  435 static ssize_t alloc_sleep_millisecs_show(struct kobject *kobj,
  436                                           struct kobj_attribute *attr,
  437                                           char *buf)
  438 {
  439         return sprintf(buf, "%u\n", khugepaged_alloc_sleep_millisecs);
  440 }
  441 
  442 static ssize_t alloc_sleep_millisecs_store(struct kobject *kobj,
  443                                            struct kobj_attribute *attr,
  444                                            const char *buf, size_t count)
  445 {
  446         unsigned long msecs;
  447         int err;
  448 
  449         err = strict_strtoul(buf, 10, &msecs);
  450         if (err || msecs > UINT_MAX)
  451                 return -EINVAL;
  452 
  453         khugepaged_alloc_sleep_millisecs = msecs;
  454         wake_up_interruptible(&khugepaged_wait);
  455 
  456         return count;
  457 }
  458 static struct kobj_attribute alloc_sleep_millisecs_attr =
  459         __ATTR(alloc_sleep_millisecs, 0644, alloc_sleep_millisecs_show,
  460                alloc_sleep_millisecs_store);
  461 
  462 static ssize_t pages_to_scan_show(struct kobject *kobj,
  463                                   struct kobj_attribute *attr,
  464                                   char *buf)
  465 {
  466         return sprintf(buf, "%u\n", khugepaged_pages_to_scan);
  467 }
  468 static ssize_t pages_to_scan_store(struct kobject *kobj,
  469                                    struct kobj_attribute *attr,
  470                                    const char *buf, size_t count)
  471 {
  472         int err;
  473         unsigned long pages;
  474 
  475         err = strict_strtoul(buf, 10, &pages);
  476         if (err || !pages || pages > UINT_MAX)
  477                 return -EINVAL;
  478 
  479         khugepaged_pages_to_scan = pages;
  480 
  481         return count;
  482 }
  483 static struct kobj_attribute pages_to_scan_attr =
  484         __ATTR(pages_to_scan, 0644, pages_to_scan_show,
  485                pages_to_scan_store);
  486 
  487 static ssize_t pages_collapsed_show(struct kobject *kobj,
  488                                     struct kobj_attribute *attr,
  489                                     char *buf)
  490 {
  491         return sprintf(buf, "%u\n", khugepaged_pages_collapsed);
  492 }
  493 static struct kobj_attribute pages_collapsed_attr =
  494         __ATTR_RO(pages_collapsed);
  495 
  496 static ssize_t full_scans_show(struct kobject *kobj,
  497                                struct kobj_attribute *attr,
  498                                char *buf)
  499 {
  500         return sprintf(buf, "%u\n", khugepaged_full_scans);
  501 }
  502 static struct kobj_attribute full_scans_attr =
  503         __ATTR_RO(full_scans);
  504 
  505 static ssize_t khugepaged_defrag_show(struct kobject *kobj,
  506                                       struct kobj_attribute *attr, char *buf)
  507 {
  508         return single_flag_show(kobj, attr, buf,
  509                                 TRANSPARENT_HUGEPAGE_DEFRAG_KHUGEPAGED_FLAG);
  510 }
  511 static ssize_t khugepaged_defrag_store(struct kobject *kobj,
  512                                        struct kobj_attribute *attr,
  513                                        const char *buf, size_t count)
  514 {
  515         return single_flag_store(kobj, attr, buf, count,
  516                                  TRANSPARENT_HUGEPAGE_DEFRAG_KHUGEPAGED_FLAG);
  517 }
  518 static struct kobj_attribute khugepaged_defrag_attr =
  519         __ATTR(defrag, 0644, khugepaged_defrag_show,
  520                khugepaged_defrag_store);
  521 
  522 /*
  523  * max_ptes_none controls if khugepaged should collapse hugepages over
  524  * any unmapped ptes in turn potentially increasing the memory
  525  * footprint of the vmas. When max_ptes_none is 0 khugepaged will not
  526  * reduce the available free memory in the system as it
  527  * runs. Increasing max_ptes_none will instead potentially reduce the
  528  * free memory in the system during the khugepaged scan.
  529  */
  530 static ssize_t khugepaged_max_ptes_none_show(struct kobject *kobj,
  531                                              struct kobj_attribute *attr,
  532                                              char *buf)
  533 {
  534         return sprintf(buf, "%u\n", khugepaged_max_ptes_none);
  535 }
  536 static ssize_t khugepaged_max_ptes_none_store(struct kobject *kobj,
  537                                               struct kobj_attribute *attr,
  538                                               const char *buf, size_t count)
  539 {
  540         int err;
  541         unsigned long max_ptes_none;
  542 
  543         err = strict_strtoul(buf, 10, &max_ptes_none);
  544         if (err || max_ptes_none > HPAGE_PMD_NR-1)
  545                 return -EINVAL;
  546 
  547         khugepaged_max_ptes_none = max_ptes_none;
  548 
  549         return count;
  550 }
  551 static struct kobj_attribute khugepaged_max_ptes_none_attr =
  552         __ATTR(max_ptes_none, 0644, khugepaged_max_ptes_none_show,
  553                khugepaged_max_ptes_none_store);
  554 
  555 static struct attribute *khugepaged_attr[] = {
  556         &khugepaged_defrag_attr.attr,
  557         &khugepaged_max_ptes_none_attr.attr,
  558         &pages_to_scan_attr.attr,
  559         &pages_collapsed_attr.attr,
  560         &full_scans_attr.attr,
  561         &scan_sleep_millisecs_attr.attr,
  562         &alloc_sleep_millisecs_attr.attr,
  563         NULL,
  564 };
  565 
  566 static struct attribute_group khugepaged_attr_group = {
  567         .attrs = khugepaged_attr,
  568         .name = "khugepaged",
  569 };
  570 
  571 static int __init hugepage_init_sysfs(struct kobject **hugepage_kobj)
  572 {
  573         int err;
  574 
  575         *hugepage_kobj = kobject_create_and_add("transparent_hugepage", mm_kobj);
  576         if (unlikely(!*hugepage_kobj)) {
  577                 printk(KERN_ERR "hugepage: failed to create transparent hugepage kobject\n");
  578                 return -ENOMEM;
  579         }
  580 
  581         err = sysfs_create_group(*hugepage_kobj, &hugepage_attr_group);
  582         if (err) {
  583                 printk(KERN_ERR "hugepage: failed to register transparent hugepage group\n");
  584                 goto delete_obj;
  585         }
  586 
  587         err = sysfs_create_group(*hugepage_kobj, &khugepaged_attr_group);
  588         if (err) {
  589                 printk(KERN_ERR "hugepage: failed to register transparent hugepage group\n");
  590                 goto remove_hp_group;
  591         }
  592 
  593         return 0;
  594 
  595 remove_hp_group:
  596         sysfs_remove_group(*hugepage_kobj, &hugepage_attr_group);
  597 delete_obj:
  598         kobject_put(*hugepage_kobj);
  599         return err;
  600 }
  601 
  602 static void __init hugepage_exit_sysfs(struct kobject *hugepage_kobj)
  603 {
  604         sysfs_remove_group(hugepage_kobj, &khugepaged_attr_group);
  605         sysfs_remove_group(hugepage_kobj, &hugepage_attr_group);
  606         kobject_put(hugepage_kobj);
  607 }
  608 #else
  609 static inline int hugepage_init_sysfs(struct kobject **hugepage_kobj)
  610 {
  611         return 0;
  612 }
  613 
  614 static inline void hugepage_exit_sysfs(struct kobject *hugepage_kobj)
  615 {
  616 }
  617 #endif /* CONFIG_SYSFS */
  618 
  619 static int __init hugepage_init(void)
  620 {
  621         int err;
  622         struct kobject *hugepage_kobj;
  623 
  624         if (!has_transparent_hugepage()) {
  625                 transparent_hugepage_flags = 0;
  626                 return -EINVAL;
  627         }
  628 
  629         err = hugepage_init_sysfs(&hugepage_kobj);
  630         if (err)
  631                 return err;
  632 
  633         err = khugepaged_slab_init();
  634         if (err)
  635                 goto out;
  636 
  637         err = mm_slots_hash_init();
  638         if (err) {
  639                 khugepaged_slab_free();
  640                 goto out;
  641         }
  642 
  643         register_shrinker(&huge_zero_page_shrinker);
  644 
  645         /*
  646          * By default disable transparent hugepages on smaller systems,
  647          * where the extra memory used could hurt more than TLB overhead
  648          * is likely to save.  The admin can still enable it through /sys.
  649          */
  650         if (totalram_pages < (512 << (20 - PAGE_SHIFT)))
  651                 transparent_hugepage_flags = 0;
  652 
  653         start_khugepaged();
  654 
  655         return 0;
  656 out:
  657         hugepage_exit_sysfs(hugepage_kobj);
  658         return err;
  659 }
  660 module_init(hugepage_init)
  661 
  662 static int __init setup_transparent_hugepage(char *str)
  663 {
  664         int ret = 0;
  665         if (!str)
  666                 goto out;
  667         if (!strcmp(str, "always")) {
  668                 set_bit(TRANSPARENT_HUGEPAGE_FLAG,
  669                         &transparent_hugepage_flags);
  670                 clear_bit(TRANSPARENT_HUGEPAGE_REQ_MADV_FLAG,
  671                           &transparent_hugepage_flags);
  672                 ret = 1;
  673         } else if (!strcmp(str, "madvise")) {
  674                 clear_bit(TRANSPARENT_HUGEPAGE_FLAG,
  675                           &transparent_hugepage_flags);
  676                 set_bit(TRANSPARENT_HUGEPAGE_REQ_MADV_FLAG,
  677                         &transparent_hugepage_flags);
  678                 ret = 1;
  679         } else if (!strcmp(str, "never")) {
  680                 clear_bit(TRANSPARENT_HUGEPAGE_FLAG,
  681                           &transparent_hugepage_flags);
  682                 clear_bit(TRANSPARENT_HUGEPAGE_REQ_MADV_FLAG,
  683                           &transparent_hugepage_flags);
  684                 ret = 1;
  685         }
  686 out:
  687         if (!ret)
  688                 printk(KERN_WARNING
  689                        "transparent_hugepage= cannot parse, ignored\n");
  690         return ret;
  691 }
  692 __setup("transparent_hugepage=", setup_transparent_hugepage);
  693 
  694 pmd_t maybe_pmd_mkwrite(pmd_t pmd, struct vm_area_struct *vma)
  695 {
  696         if (likely(vma->vm_flags & VM_WRITE))
  697                 pmd = pmd_mkwrite(pmd);
  698         return pmd;
  699 }
  700 
  701 static inline pmd_t mk_huge_pmd(struct page *page, struct vm_area_struct *vma)
  702 {
  703         pmd_t entry;
  704         entry = mk_pmd(page, vma->vm_page_prot);
  705         entry = maybe_pmd_mkwrite(pmd_mkdirty(entry), vma);
  706         entry = pmd_mkhuge(entry);
  707         return entry;
  708 }
  709 
  710 static int __do_huge_pmd_anonymous_page(struct mm_struct *mm,
  711                                         struct vm_area_struct *vma,
  712                                         unsigned long haddr, pmd_t *pmd,
  713                                         struct page *page)
  714 {
  715         pgtable_t pgtable;
  716 
  717         VM_BUG_ON(!PageCompound(page));
  718         pgtable = pte_alloc_one(mm, haddr);
  719         if (unlikely(!pgtable))
  720                 return VM_FAULT_OOM;
  721 
  722         clear_huge_page(page, haddr, HPAGE_PMD_NR);
  723         __SetPageUptodate(page);
  724 
  725         spin_lock(&mm->page_table_lock);
  726         if (unlikely(!pmd_none(*pmd))) {
  727                 spin_unlock(&mm->page_table_lock);
  728                 mem_cgroup_uncharge_page(page);
  729                 put_page(page);
  730                 pte_free(mm, pgtable);
  731         } else {
  732                 pmd_t entry;
  733                 entry = mk_huge_pmd(page, vma);
  734                 /*
  735                  * The spinlocking to take the lru_lock inside
  736                  * page_add_new_anon_rmap() acts as a full memory
  737                  * barrier to be sure clear_huge_page writes become
  738                  * visible after the set_pmd_at() write.
  739                  */
  740                 page_add_new_anon_rmap(page, vma, haddr);
  741                 set_pmd_at(mm, haddr, pmd, entry);
  742                 pgtable_trans_huge_deposit(mm, pgtable);
  743                 add_mm_counter(mm, MM_ANONPAGES, HPAGE_PMD_NR);
  744                 mm->nr_ptes++;
  745                 spin_unlock(&mm->page_table_lock);
  746         }
  747 
  748         return 0;
  749 }
  750 
  751 static inline gfp_t alloc_hugepage_gfpmask(int defrag, gfp_t extra_gfp)
  752 {
  753         return (GFP_TRANSHUGE & ~(defrag ? 0 : __GFP_WAIT)) | extra_gfp;
  754 }
  755 
  756 static inline struct page *alloc_hugepage_vma(int defrag,
  757                                               struct vm_area_struct *vma,
  758                                               unsigned long haddr, int nd,
  759                                               gfp_t extra_gfp)
  760 {
  761         return alloc_pages_vma(alloc_hugepage_gfpmask(defrag, extra_gfp),
  762                                HPAGE_PMD_ORDER, vma, haddr, nd);
  763 }
  764 
  765 #ifndef CONFIG_NUMA
  766 static inline struct page *alloc_hugepage(int defrag)
  767 {
  768         return alloc_pages(alloc_hugepage_gfpmask(defrag, 0),
  769                            HPAGE_PMD_ORDER);
  770 }
  771 #endif
  772 
  773 static bool set_huge_zero_page(pgtable_t pgtable, struct mm_struct *mm,
  774                 struct vm_area_struct *vma, unsigned long haddr, pmd_t *pmd,
  775                 unsigned long zero_pfn)
  776 {
  777         pmd_t entry;
  778         if (!pmd_none(*pmd))
  779                 return false;
  780         entry = pfn_pmd(zero_pfn, vma->vm_page_prot);
  781         entry = pmd_wrprotect(entry);
  782         entry = pmd_mkhuge(entry);
  783         set_pmd_at(mm, haddr, pmd, entry);
  784         pgtable_trans_huge_deposit(mm, pgtable);
  785         mm->nr_ptes++;
  786         return true;
  787 }
  788 
  789 int do_huge_pmd_anonymous_page(struct mm_struct *mm, struct vm_area_struct *vma,
  790                                unsigned long address, pmd_t *pmd,
  791                                unsigned int flags)
  792 {
  793         struct page *page;
  794         unsigned long haddr = address & HPAGE_PMD_MASK;
  795         pte_t *pte;
  796 
  797         if (haddr >= vma->vm_start && haddr + HPAGE_PMD_SIZE <= vma->vm_end) {
  798                 if (unlikely(anon_vma_prepare(vma)))
  799                         return VM_FAULT_OOM;
  800                 if (unlikely(khugepaged_enter(vma)))
  801                         return VM_FAULT_OOM;
  802                 if (!(flags & FAULT_FLAG_WRITE) &&
  803                                 transparent_hugepage_use_zero_page()) {
  804                         pgtable_t pgtable;
  805                         unsigned long zero_pfn;
  806                         bool set;
  807                         pgtable = pte_alloc_one(mm, haddr);
  808                         if (unlikely(!pgtable))
  809                                 return VM_FAULT_OOM;
  810                         zero_pfn = get_huge_zero_page();
  811                         if (unlikely(!zero_pfn)) {
  812                                 pte_free(mm, pgtable);
  813                                 count_vm_event(THP_FAULT_FALLBACK);
  814                                 goto out;
  815                         }
  816                         spin_lock(&mm->page_table_lock);
  817                         set = set_huge_zero_page(pgtable, mm, vma, haddr, pmd,
  818                                         zero_pfn);
  819                         spin_unlock(&mm->page_table_lock);
  820                         if (!set) {
  821                                 pte_free(mm, pgtable);
  822                                 put_huge_zero_page();
  823                         }
  824                         return 0;
  825                 }
  826                 page = alloc_hugepage_vma(transparent_hugepage_defrag(vma),
  827                                           vma, haddr, numa_node_id(), 0);
  828                 if (unlikely(!page)) {
  829                         count_vm_event(THP_FAULT_FALLBACK);
  830                         goto out;
  831                 }
  832                 count_vm_event(THP_FAULT_ALLOC);
  833                 if (unlikely(mem_cgroup_newpage_charge(page, mm, GFP_KERNEL))) {
  834                         put_page(page);
  835                         goto out;
  836                 }
  837                 if (unlikely(__do_huge_pmd_anonymous_page(mm, vma, haddr, pmd,
  838                                                           page))) {
  839                         mem_cgroup_uncharge_page(page);
  840                         put_page(page);
  841                         goto out;
  842                 }
  843 
  844                 return 0;
  845         }
  846 out:
  847         /*
  848          * Use __pte_alloc instead of pte_alloc_map, because we can't
  849          * run pte_offset_map on the pmd, if an huge pmd could
  850          * materialize from under us from a different thread.
  851          */
  852         if (unlikely(pmd_none(*pmd)) &&
  853             unlikely(__pte_alloc(mm, vma, pmd, address)))
  854                 return VM_FAULT_OOM;
  855         /* if an huge pmd materialized from under us just retry later */
  856         if (unlikely(pmd_trans_huge(*pmd)))
  857                 return 0;
  858         /*
  859          * A regular pmd is established and it can't morph into a huge pmd
  860          * from under us anymore at this point because we hold the mmap_sem
  861          * read mode and khugepaged takes it in write mode. So now it's
  862          * safe to run pte_offset_map().
  863          */
  864         pte = pte_offset_map(pmd, address);
  865         return handle_pte_fault(mm, vma, address, pte, pmd, flags);
  866 }
  867 
  868 int copy_huge_pmd(struct mm_struct *dst_mm, struct mm_struct *src_mm,
  869                   pmd_t *dst_pmd, pmd_t *src_pmd, unsigned long addr,
  870                   struct vm_area_struct *vma)
  871 {
  872         struct page *src_page;
  873         pmd_t pmd;
  874         pgtable_t pgtable;
  875         int ret;
  876 
  877         ret = -ENOMEM;
  878         pgtable = pte_alloc_one(dst_mm, addr);
  879         if (unlikely(!pgtable))
  880                 goto out;
  881 
  882         spin_lock(&dst_mm->page_table_lock);
  883         spin_lock_nested(&src_mm->page_table_lock, SINGLE_DEPTH_NESTING);
  884 
  885         ret = -EAGAIN;
  886         pmd = *src_pmd;
  887         if (unlikely(!pmd_trans_huge(pmd))) {
  888                 pte_free(dst_mm, pgtable);
  889                 goto out_unlock;
  890         }
  891         /*
  892          * mm->page_table_lock is enough to be sure that huge zero pmd is not
  893          * under splitting since we don't split the page itself, only pmd to
  894          * a page table.
  895          */
  896         if (is_huge_zero_pmd(pmd)) {
  897                 unsigned long zero_pfn;
  898                 bool set;
  899                 /*
  900                  * get_huge_zero_page() will never allocate a new page here,
  901                  * since we already have a zero page to copy. It just takes a
  902                  * reference.
  903                  */
  904                 zero_pfn = get_huge_zero_page();
  905                 set = set_huge_zero_page(pgtable, dst_mm, vma, addr, dst_pmd,
  906                                 zero_pfn);
  907                 BUG_ON(!set); /* unexpected !pmd_none(dst_pmd) */
  908                 ret = 0;
  909                 goto out_unlock;
  910         }
  911         if (unlikely(pmd_trans_splitting(pmd))) {
  912                 /* split huge page running from under us */
  913                 spin_unlock(&src_mm->page_table_lock);
  914                 spin_unlock(&dst_mm->page_table_lock);
  915                 pte_free(dst_mm, pgtable);
  916 
  917                 wait_split_huge_page(vma->anon_vma, src_pmd); /* src_vma */
  918                 goto out;
  919         }
  920         src_page = pmd_page(pmd);
  921         VM_BUG_ON(!PageHead(src_page));
  922         get_page(src_page);
  923         page_dup_rmap(src_page);
  924         add_mm_counter(dst_mm, MM_ANONPAGES, HPAGE_PMD_NR);
  925 
  926         pmdp_set_wrprotect(src_mm, addr, src_pmd);
  927         pmd = pmd_mkold(pmd_wrprotect(pmd));
  928         set_pmd_at(dst_mm, addr, dst_pmd, pmd);
  929         pgtable_trans_huge_deposit(dst_mm, pgtable);
  930         dst_mm->nr_ptes++;
  931 
  932         ret = 0;
  933 out_unlock:
  934         spin_unlock(&src_mm->page_table_lock);
  935         spin_unlock(&dst_mm->page_table_lock);
  936 out:
  937         return ret;
  938 }
  939 
  940 void huge_pmd_set_accessed(struct mm_struct *mm,
  941                            struct vm_area_struct *vma,
  942                            unsigned long address,
  943                            pmd_t *pmd, pmd_t orig_pmd,
  944                            int dirty)
  945 {
  946         pmd_t entry;
  947         unsigned long haddr;
  948 
  949         spin_lock(&mm->page_table_lock);
  950         if (unlikely(!pmd_same(*pmd, orig_pmd)))
  951                 goto unlock;
  952 
  953         entry = pmd_mkyoung(orig_pmd);
  954         haddr = address & HPAGE_PMD_MASK;
  955         if (pmdp_set_access_flags(vma, haddr, pmd, entry, dirty))
  956                 update_mmu_cache_pmd(vma, address, pmd);
  957 
  958 unlock:
  959         spin_unlock(&mm->page_table_lock);
  960 }
  961 
  962 static int do_huge_pmd_wp_zero_page_fallback(struct mm_struct *mm,
  963                 struct vm_area_struct *vma, unsigned long address,
  964                 pmd_t *pmd, pmd_t orig_pmd, unsigned long haddr)
  965 {
  966         pgtable_t pgtable;
  967         pmd_t _pmd;
  968         struct page *page;
  969         int i, ret = 0;
  970         unsigned long mmun_start;       /* For mmu_notifiers */
  971         unsigned long mmun_end;         /* For mmu_notifiers */
  972 
  973         page = alloc_page_vma(GFP_HIGHUSER_MOVABLE, vma, address);
  974         if (!page) {
  975                 ret |= VM_FAULT_OOM;
  976                 goto out;
  977         }
  978 
  979         if (mem_cgroup_newpage_charge(page, mm, GFP_KERNEL)) {
  980                 put_page(page);
  981                 ret |= VM_FAULT_OOM;
  982                 goto out;
  983         }
  984 
  985         clear_user_highpage(page, address);
  986         __SetPageUptodate(page);
  987 
  988         mmun_start = haddr;
  989         mmun_end   = haddr + HPAGE_PMD_SIZE;
  990         mmu_notifier_invalidate_range_start(mm, mmun_start, mmun_end);
  991 
  992         spin_lock(&mm->page_table_lock);
  993         if (unlikely(!pmd_same(*pmd, orig_pmd)))
  994                 goto out_free_page;
  995 
  996         pmdp_clear_flush(vma, haddr, pmd);
  997         /* leave pmd empty until pte is filled */
  998 
  999         pgtable = pgtable_trans_huge_withdraw(mm);
 1000         pmd_populate(mm, &_pmd, pgtable);
 1001 
 1002         for (i = 0; i < HPAGE_PMD_NR; i++, haddr += PAGE_SIZE) {
 1003                 pte_t *pte, entry;
 1004                 if (haddr == (address & PAGE_MASK)) {
 1005                         entry = mk_pte(page, vma->vm_page_prot);
 1006                         entry = maybe_mkwrite(pte_mkdirty(entry), vma);
 1007                         page_add_new_anon_rmap(page, vma, haddr);
 1008                 } else {
 1009                         entry = pfn_pte(my_zero_pfn(haddr), vma->vm_page_prot);
 1010                         entry = pte_mkspecial(entry);
 1011                 }
 1012                 pte = pte_offset_map(&_pmd, haddr);
 1013                 VM_BUG_ON(!pte_none(*pte));
 1014                 set_pte_at(mm, haddr, pte, entry);
 1015                 pte_unmap(pte);
 1016         }
 1017         smp_wmb(); /* make pte visible before pmd */
 1018         pmd_populate(mm, pmd, pgtable);
 1019         spin_unlock(&mm->page_table_lock);
 1020         put_huge_zero_page();
 1021         inc_mm_counter(mm, MM_ANONPAGES);
 1022 
 1023         mmu_notifier_invalidate_range_end(mm, mmun_start, mmun_end);
 1024 
 1025         ret |= VM_FAULT_WRITE;
 1026 out:
 1027         return ret;
 1028 out_free_page:
 1029         spin_unlock(&mm->page_table_lock);
 1030         mmu_notifier_invalidate_range_end(mm, mmun_start, mmun_end);
 1031         mem_cgroup_uncharge_page(page);
 1032         put_page(page);
 1033         goto out;
 1034 }
 1035 
 1036 static int do_huge_pmd_wp_page_fallback(struct mm_struct *mm,
 1037                                         struct vm_area_struct *vma,
 1038                                         unsigned long address,
 1039                                         pmd_t *pmd, pmd_t orig_pmd,
 1040                                         struct page *page,
 1041                                         unsigned long haddr)
 1042 {
 1043         pgtable_t pgtable;
 1044         pmd_t _pmd;
 1045         int ret = 0, i;
 1046         struct page **pages;
 1047         unsigned long mmun_start;       /* For mmu_notifiers */
 1048         unsigned long mmun_end;         /* For mmu_notifiers */
 1049 
 1050         pages = kmalloc(sizeof(struct page *) * HPAGE_PMD_NR,
 1051                         GFP_KERNEL);
 1052         if (unlikely(!pages)) {
 1053                 ret |= VM_FAULT_OOM;
 1054                 goto out;
 1055         }
 1056 
 1057         for (i = 0; i < HPAGE_PMD_NR; i++) {
 1058                 pages[i] = alloc_page_vma_node(GFP_HIGHUSER_MOVABLE |
 1059                                                __GFP_OTHER_NODE,
 1060                                                vma, address, page_to_nid(page));
 1061                 if (unlikely(!pages[i] ||
 1062                              mem_cgroup_newpage_charge(pages[i], mm,
 1063                                                        GFP_KERNEL))) {
 1064                         if (pages[i])
 1065                                 put_page(pages[i]);
 1066                         mem_cgroup_uncharge_start();
 1067                         while (--i >= 0) {
 1068                                 mem_cgroup_uncharge_page(pages[i]);
 1069                                 put_page(pages[i]);
 1070                         }
 1071                         mem_cgroup_uncharge_end();
 1072                         kfree(pages);
 1073                         ret |= VM_FAULT_OOM;
 1074                         goto out;
 1075                 }
 1076         }
 1077 
 1078         for (i = 0; i < HPAGE_PMD_NR; i++) {
 1079                 copy_user_highpage(pages[i], page + i,
 1080                                    haddr + PAGE_SIZE * i, vma);
 1081                 __SetPageUptodate(pages[i]);
 1082                 cond_resched();
 1083         }
 1084 
 1085         mmun_start = haddr;
 1086         mmun_end   = haddr + HPAGE_PMD_SIZE;
 1087         mmu_notifier_invalidate_range_start(mm, mmun_start, mmun_end);
 1088 
 1089         spin_lock(&mm->page_table_lock);
 1090         if (unlikely(!pmd_same(*pmd, orig_pmd)))
 1091                 goto out_free_pages;
 1092         VM_BUG_ON(!PageHead(page));
 1093 
 1094         pmdp_clear_flush(vma, haddr, pmd);
 1095         /* leave pmd empty until pte is filled */
 1096 
 1097         pgtable = pgtable_trans_huge_withdraw(mm);
 1098         pmd_populate(mm, &_pmd, pgtable);
 1099 
 1100         for (i = 0; i < HPAGE_PMD_NR; i++, haddr += PAGE_SIZE) {
 1101                 pte_t *pte, entry;
 1102                 entry = mk_pte(pages[i], vma->vm_page_prot);
 1103                 entry = maybe_mkwrite(pte_mkdirty(entry), vma);
 1104                 page_add_new_anon_rmap(pages[i], vma, haddr);
 1105                 pte = pte_offset_map(&_pmd, haddr);
 1106                 VM_BUG_ON(!pte_none(*pte));
 1107                 set_pte_at(mm, haddr, pte, entry);
 1108                 pte_unmap(pte);
 1109         }
 1110         kfree(pages);
 1111 
 1112         smp_wmb(); /* make pte visible before pmd */
 1113         pmd_populate(mm, pmd, pgtable);
 1114         page_remove_rmap(page);
 1115         spin_unlock(&mm->page_table_lock);
 1116 
 1117         mmu_notifier_invalidate_range_end(mm, mmun_start, mmun_end);
 1118 
 1119         ret |= VM_FAULT_WRITE;
 1120         put_page(page);
 1121 
 1122 out:
 1123         return ret;
 1124 
 1125 out_free_pages:
 1126         spin_unlock(&mm->page_table_lock);
 1127         mmu_notifier_invalidate_range_end(mm, mmun_start, mmun_end);
 1128         mem_cgroup_uncharge_start();
 1129         for (i = 0; i < HPAGE_PMD_NR; i++) {
 1130                 mem_cgroup_uncharge_page(pages[i]);
 1131                 put_page(pages[i]);
 1132         }
 1133         mem_cgroup_uncharge_end();
 1134         kfree(pages);
 1135         goto out;
 1136 }
 1137 
 1138 int do_huge_pmd_wp_page(struct mm_struct *mm, struct vm_area_struct *vma,
 1139                         unsigned long address, pmd_t *pmd, pmd_t orig_pmd)
 1140 {
 1141         int ret = 0;
 1142         struct page *page = NULL, *new_page;
 1143         unsigned long haddr;
 1144         unsigned long mmun_start;       /* For mmu_notifiers */
 1145         unsigned long mmun_end;         /* For mmu_notifiers */
 1146 
 1147         VM_BUG_ON(!vma->anon_vma);
 1148         haddr = address & HPAGE_PMD_MASK;
 1149         if (is_huge_zero_pmd(orig_pmd))
 1150                 goto alloc;
 1151         spin_lock(&mm->page_table_lock);
 1152         if (unlikely(!pmd_same(*pmd, orig_pmd)))
 1153                 goto out_unlock;
 1154 
 1155         page = pmd_page(orig_pmd);
 1156         VM_BUG_ON(!PageCompound(page) || !PageHead(page));
 1157         if (page_mapcount(page) == 1) {
 1158                 pmd_t entry;
 1159                 entry = pmd_mkyoung(orig_pmd);
 1160                 entry = maybe_pmd_mkwrite(pmd_mkdirty(entry), vma);
 1161                 if (pmdp_set_access_flags(vma, haddr, pmd, entry,  1))
 1162                         update_mmu_cache_pmd(vma, address, pmd);
 1163                 ret |= VM_FAULT_WRITE;
 1164                 goto out_unlock;
 1165         }
 1166         get_page(page);
 1167         spin_unlock(&mm->page_table_lock);
 1168 alloc:
 1169         if (transparent_hugepage_enabled(vma) &&
 1170             !transparent_hugepage_debug_cow())
 1171                 new_page = alloc_hugepage_vma(transparent_hugepage_defrag(vma),
 1172                                               vma, haddr, numa_node_id(), 0);
 1173         else
 1174                 new_page = NULL;
 1175 
 1176         if (unlikely(!new_page)) {
 1177                 count_vm_event(THP_FAULT_FALLBACK);
 1178                 if (is_huge_zero_pmd(orig_pmd)) {
 1179                         ret = do_huge_pmd_wp_zero_page_fallback(mm, vma,
 1180                                         address, pmd, orig_pmd, haddr);
 1181                 } else {
 1182                         ret = do_huge_pmd_wp_page_fallback(mm, vma, address,
 1183                                         pmd, orig_pmd, page, haddr);
 1184                         if (ret & VM_FAULT_OOM)
 1185                                 split_huge_page(page);
 1186                         put_page(page);
 1187                 }
 1188                 goto out;
 1189         }
 1190         count_vm_event(THP_FAULT_ALLOC);
 1191 
 1192         if (unlikely(mem_cgroup_newpage_charge(new_page, mm, GFP_KERNEL))) {
 1193                 put_page(new_page);
 1194                 if (page) {
 1195                         split_huge_page(page);
 1196                         put_page(page);
 1197                 }
 1198                 ret |= VM_FAULT_OOM;
 1199                 goto out;
 1200         }
 1201 
 1202         if (is_huge_zero_pmd(orig_pmd))
 1203                 clear_huge_page(new_page, haddr, HPAGE_PMD_NR);
 1204         else
 1205                 copy_user_huge_page(new_page, page, haddr, vma, HPAGE_PMD_NR);
 1206         __SetPageUptodate(new_page);
 1207 
 1208         mmun_start = haddr;
 1209         mmun_end   = haddr + HPAGE_PMD_SIZE;
 1210         mmu_notifier_invalidate_range_start(mm, mmun_start, mmun_end);
 1211 
 1212         spin_lock(&mm->page_table_lock);
 1213         if (page)
 1214                 put_page(page);
 1215         if (unlikely(!pmd_same(*pmd, orig_pmd))) {
 1216                 spin_unlock(&mm->page_table_lock);
 1217                 mem_cgroup_uncharge_page(new_page);
 1218                 put_page(new_page);
 1219                 goto out_mn;
 1220         } else {
 1221                 pmd_t entry;
 1222                 entry = mk_huge_pmd(new_page, vma);
 1223                 pmdp_clear_flush(vma, haddr, pmd);
 1224                 page_add_new_anon_rmap(new_page, vma, haddr);
 1225                 set_pmd_at(mm, haddr, pmd, entry);
 1226                 update_mmu_cache_pmd(vma, address, pmd);
 1227                 if (is_huge_zero_pmd(orig_pmd)) {
 1228                         add_mm_counter(mm, MM_ANONPAGES, HPAGE_PMD_NR);
 1229                         put_huge_zero_page();
 1230                 } else {
 1231                         VM_BUG_ON(!PageHead(page));
 1232                         page_remove_rmap(page);
 1233                         put_page(page);
 1234                 }
 1235                 ret |= VM_FAULT_WRITE;
 1236         }
 1237         spin_unlock(&mm->page_table_lock);
 1238 out_mn:
 1239         mmu_notifier_invalidate_range_end(mm, mmun_start, mmun_end);
 1240 out:
 1241         return ret;
 1242 out_unlock:
 1243         spin_unlock(&mm->page_table_lock);
 1244         return ret;
 1245 }
 1246 
 1247 struct page *follow_trans_huge_pmd(struct vm_area_struct *vma,
 1248                                    unsigned long addr,
 1249                                    pmd_t *pmd,
 1250                                    unsigned int flags)
 1251 {
 1252         struct mm_struct *mm = vma->vm_mm;
 1253         struct page *page = NULL;
 1254 
 1255         assert_spin_locked(&mm->page_table_lock);
 1256 
 1257         if (flags & FOLL_WRITE && !pmd_write(*pmd))
 1258                 goto out;
 1259 
 1260         page = pmd_page(*pmd);
 1261         VM_BUG_ON(!PageHead(page));
 1262         if (flags & FOLL_TOUCH) {
 1263                 pmd_t _pmd;
 1264                 /*
 1265                  * We should set the dirty bit only for FOLL_WRITE but
 1266                  * for now the dirty bit in the pmd is meaningless.
 1267                  * And if the dirty bit will become meaningful and
 1268                  * we'll only set it with FOLL_WRITE, an atomic
 1269                  * set_bit will be required on the pmd to set the
 1270                  * young bit, instead of the current set_pmd_at.
 1271                  */
 1272                 _pmd = pmd_mkyoung(pmd_mkdirty(*pmd));
 1273                 set_pmd_at(mm, addr & HPAGE_PMD_MASK, pmd, _pmd);
 1274         }
 1275         if ((flags & FOLL_MLOCK) && (vma->vm_flags & VM_LOCKED)) {
 1276                 if (page->mapping && trylock_page(page)) {
 1277                         lru_add_drain();
 1278                         if (page->mapping)
 1279                                 mlock_vma_page(page);
 1280                         unlock_page(page);
 1281                 }
 1282         }
 1283         page += (addr & ~HPAGE_PMD_MASK) >> PAGE_SHIFT;
 1284         VM_BUG_ON(!PageCompound(page));
 1285         if (flags & FOLL_GET)
 1286                 get_page_foll(page);
 1287 
 1288 out:
 1289         return page;
 1290 }
 1291 
 1292 /* NUMA hinting page fault entry point for trans huge pmds */
 1293 int do_huge_pmd_numa_page(struct mm_struct *mm, struct vm_area_struct *vma,
 1294                                 unsigned long addr, pmd_t pmd, pmd_t *pmdp)
 1295 {
 1296         struct page *page;
 1297         unsigned long haddr = addr & HPAGE_PMD_MASK;
 1298         int target_nid;
 1299         int current_nid = -1;
 1300         bool migrated;
 1301         bool page_locked = false;
 1302 
 1303         spin_lock(&mm->page_table_lock);
 1304         if (unlikely(!pmd_same(pmd, *pmdp)))
 1305                 goto out_unlock;
 1306 
 1307         page = pmd_page(pmd);
 1308         get_page(page);
 1309         current_nid = page_to_nid(page);
 1310         count_vm_numa_event(NUMA_HINT_FAULTS);
 1311         if (current_nid == numa_node_id())
 1312                 count_vm_numa_event(NUMA_HINT_FAULTS_LOCAL);
 1313 
 1314         target_nid = mpol_misplaced(page, vma, haddr);
 1315         if (target_nid == -1) {
 1316                 put_page(page);
 1317                 goto clear_pmdnuma;
 1318         }
 1319 
 1320         /* Acquire the page lock to serialise THP migrations */
 1321         spin_unlock(&mm->page_table_lock);
 1322         lock_page(page);
 1323         page_locked = true;
 1324 
 1325         /* Confirm the PTE did not while locked */
 1326         spin_lock(&mm->page_table_lock);
 1327         if (unlikely(!pmd_same(pmd, *pmdp))) {
 1328                 unlock_page(page);
 1329                 put_page(page);
 1330                 goto out_unlock;
 1331         }
 1332         spin_unlock(&mm->page_table_lock);
 1333 
 1334         /* Migrate the THP to the requested node */
 1335         migrated = migrate_misplaced_transhuge_page(mm, vma,
 1336                                 pmdp, pmd, addr,
 1337                                 page, target_nid);
 1338         if (migrated)
 1339                 current_nid = target_nid;
 1340         else {
 1341                 spin_lock(&mm->page_table_lock);
 1342                 if (unlikely(!pmd_same(pmd, *pmdp))) {
 1343                         unlock_page(page);
 1344                         goto out_unlock;
 1345                 }
 1346                 goto clear_pmdnuma;
 1347         }
 1348 
 1349         task_numa_fault(current_nid, HPAGE_PMD_NR, migrated);
 1350         return 0;
 1351 
 1352 clear_pmdnuma:
 1353         pmd = pmd_mknonnuma(pmd);
 1354         set_pmd_at(mm, haddr, pmdp, pmd);
 1355         VM_BUG_ON(pmd_numa(*pmdp));
 1356         update_mmu_cache_pmd(vma, addr, pmdp);
 1357         if (page_locked)
 1358                 unlock_page(page);
 1359 
 1360 out_unlock:
 1361         spin_unlock(&mm->page_table_lock);
 1362         if (current_nid != -1)
 1363                 task_numa_fault(current_nid, HPAGE_PMD_NR, migrated);
 1364         return 0;
 1365 }
 1366 
 1367 int zap_huge_pmd(struct mmu_gather *tlb, struct vm_area_struct *vma,
 1368                  pmd_t *pmd, unsigned long addr)
 1369 {
 1370         int ret = 0;
 1371 
 1372         if (__pmd_trans_huge_lock(pmd, vma) == 1) {
 1373                 struct page *page;
 1374                 pgtable_t pgtable;
 1375                 pmd_t orig_pmd;
 1376                 pgtable = pgtable_trans_huge_withdraw(tlb->mm);
 1377                 orig_pmd = pmdp_get_and_clear(tlb->mm, addr, pmd);
 1378                 tlb_remove_pmd_tlb_entry(tlb, pmd, addr);
 1379                 if (is_huge_zero_pmd(orig_pmd)) {
 1380                         tlb->mm->nr_ptes--;
 1381                         spin_unlock(&tlb->mm->page_table_lock);
 1382                         put_huge_zero_page();
 1383                 } else {
 1384                         page = pmd_page(orig_pmd);
 1385                         page_remove_rmap(page);
 1386                         VM_BUG_ON(page_mapcount(page) < 0);
 1387                         add_mm_counter(tlb->mm, MM_ANONPAGES, -HPAGE_PMD_NR);
 1388                         VM_BUG_ON(!PageHead(page));
 1389                         tlb->mm->nr_ptes--;
 1390                         spin_unlock(&tlb->mm->page_table_lock);
 1391                         tlb_remove_page(tlb, page);
 1392                 }
 1393                 pte_free(tlb->mm, pgtable);
 1394                 ret = 1;
 1395         }
 1396         return ret;
 1397 }
 1398 
 1399 int mincore_huge_pmd(struct vm_area_struct *vma, pmd_t *pmd,
 1400                 unsigned long addr, unsigned long end,
 1401                 unsigned char *vec)
 1402 {
 1403         int ret = 0;
 1404 
 1405         if (__pmd_trans_huge_lock(pmd, vma) == 1) {
 1406                 /*
 1407                  * All logical pages in the range are present
 1408                  * if backed by a huge page.
 1409                  */
 1410                 spin_unlock(&vma->vm_mm->page_table_lock);
 1411                 memset(vec, 1, (end - addr) >> PAGE_SHIFT);
 1412                 ret = 1;
 1413         }
 1414 
 1415         return ret;
 1416 }
 1417 
 1418 int move_huge_pmd(struct vm_area_struct *vma, struct vm_area_struct *new_vma,
 1419                   unsigned long old_addr,
 1420                   unsigned long new_addr, unsigned long old_end,
 1421                   pmd_t *old_pmd, pmd_t *new_pmd)
 1422 {
 1423         int ret = 0;
 1424         pmd_t pmd;
 1425 
 1426         struct mm_struct *mm = vma->vm_mm;
 1427 
 1428         if ((old_addr & ~HPAGE_PMD_MASK) ||
 1429             (new_addr & ~HPAGE_PMD_MASK) ||
 1430             old_end - old_addr < HPAGE_PMD_SIZE ||
 1431             (new_vma->vm_flags & VM_NOHUGEPAGE))
 1432                 goto out;
 1433 
 1434         /*
 1435          * The destination pmd shouldn't be established, free_pgtables()
 1436          * should have release it.
 1437          */
 1438         if (WARN_ON(!pmd_none(*new_pmd))) {
 1439                 VM_BUG_ON(pmd_trans_huge(*new_pmd));
 1440                 goto out;
 1441         }
 1442 
 1443         ret = __pmd_trans_huge_lock(old_pmd, vma);
 1444         if (ret == 1) {
 1445                 pmd = pmdp_get_and_clear(mm, old_addr, old_pmd);
 1446                 VM_BUG_ON(!pmd_none(*new_pmd));
 1447                 set_pmd_at(mm, new_addr, new_pmd, pmd);
 1448                 spin_unlock(&mm->page_table_lock);
 1449         }
 1450 out:
 1451         return ret;
 1452 }
 1453 
 1454 int change_huge_pmd(struct vm_area_struct *vma, pmd_t *pmd,
 1455                 unsigned long addr, pgprot_t newprot, int prot_numa)
 1456 {
 1457         struct mm_struct *mm = vma->vm_mm;
 1458         int ret = 0;
 1459 
 1460         if (__pmd_trans_huge_lock(pmd, vma) == 1) {
 1461                 pmd_t entry;
 1462                 entry = pmdp_get_and_clear(mm, addr, pmd);
 1463                 if (!prot_numa) {
 1464                         entry = pmd_modify(entry, newprot);
 1465                         BUG_ON(pmd_write(entry));
 1466                 } else {
 1467                         struct page *page = pmd_page(*pmd);
 1468 
 1469                         /* only check non-shared pages */
 1470                         if (page_mapcount(page) == 1 &&
 1471                             !pmd_numa(*pmd)) {
 1472                                 entry = pmd_mknuma(entry);
 1473                         }
 1474                 }
 1475                 set_pmd_at(mm, addr, pmd, entry);
 1476                 spin_unlock(&vma->vm_mm->page_table_lock);
 1477                 ret = 1;
 1478         }
 1479 
 1480         return ret;
 1481 }
 1482 
 1483 /*
 1484  * Returns 1 if a given pmd maps a stable (not under splitting) thp.
 1485  * Returns -1 if it maps a thp under splitting. Returns 0 otherwise.
 1486  *
 1487  * Note that if it returns 1, this routine returns without unlocking page
 1488  * table locks. So callers must unlock them.
 1489  */
 1490 int __pmd_trans_huge_lock(pmd_t *pmd, struct vm_area_struct *vma)
 1491 {
 1492         spin_lock(&vma->vm_mm->page_table_lock);
 1493         if (likely(pmd_trans_huge(*pmd))) {
 1494                 if (unlikely(pmd_trans_splitting(*pmd))) {
 1495                         spin_unlock(&vma->vm_mm->page_table_lock);
 1496                         wait_split_huge_page(vma->anon_vma, pmd);
 1497                         return -1;
 1498                 } else {
 1499                         /* Thp mapped by 'pmd' is stable, so we can
 1500                          * handle it as it is. */
 1501                         return 1;
 1502                 }
 1503         }
 1504         spin_unlock(&vma->vm_mm->page_table_lock);
 1505         return 0;
 1506 }
 1507 
 1508 pmd_t *page_check_address_pmd(struct page *page,
 1509                               struct mm_struct *mm,
 1510                               unsigned long address,
 1511                               enum page_check_address_pmd_flag flag)
 1512 {
 1513         pmd_t *pmd, *ret = NULL;
 1514 
 1515         if (address & ~HPAGE_PMD_MASK)
 1516                 goto out;
 1517 
 1518         pmd = mm_find_pmd(mm, address);
 1519         if (!pmd)
 1520                 goto out;
 1521         if (pmd_none(*pmd))
 1522                 goto out;
 1523         if (pmd_page(*pmd) != page)
 1524                 goto out;
 1525         /*
 1526          * split_vma() may create temporary aliased mappings. There is
 1527          * no risk as long as all huge pmd are found and have their
 1528          * splitting bit set before __split_huge_page_refcount
 1529          * runs. Finding the same huge pmd more than once during the
 1530          * same rmap walk is not a problem.
 1531          */
 1532         if (flag == PAGE_CHECK_ADDRESS_PMD_NOTSPLITTING_FLAG &&
 1533             pmd_trans_splitting(*pmd))
 1534                 goto out;
 1535         if (pmd_trans_huge(*pmd)) {
 1536                 VM_BUG_ON(flag == PAGE_CHECK_ADDRESS_PMD_SPLITTING_FLAG &&
 1537                           !pmd_trans_splitting(*pmd));
 1538                 ret = pmd;
 1539         }
 1540 out:
 1541         return ret;
 1542 }
 1543 
 1544 static int __split_huge_page_splitting(struct page *page,
 1545                                        struct vm_area_struct *vma,
 1546                                        unsigned long address)
 1547 {
 1548         struct mm_struct *mm = vma->vm_mm;
 1549         pmd_t *pmd;
 1550         int ret = 0;
 1551         /* For mmu_notifiers */
 1552         const unsigned long mmun_start = address;
 1553         const unsigned long mmun_end   = address + HPAGE_PMD_SIZE;
 1554 
 1555         mmu_notifier_invalidate_range_start(mm, mmun_start, mmun_end);
 1556         spin_lock(&mm->page_table_lock);
 1557         pmd = page_check_address_pmd(page, mm, address,
 1558                                      PAGE_CHECK_ADDRESS_PMD_NOTSPLITTING_FLAG);
 1559         if (pmd) {
 1560                 /*
 1561                  * We can't temporarily set the pmd to null in order
 1562                  * to split it, the pmd must remain marked huge at all
 1563                  * times or the VM won't take the pmd_trans_huge paths
 1564                  * and it won't wait on the anon_vma->root->rwsem to
 1565                  * serialize against split_huge_page*.
 1566                  */
 1567                 pmdp_splitting_flush(vma, address, pmd);
 1568                 ret = 1;
 1569         }
 1570         spin_unlock(&mm->page_table_lock);
 1571         mmu_notifier_invalidate_range_end(mm, mmun_start, mmun_end);
 1572 
 1573         return ret;
 1574 }
 1575 
 1576 static void __split_huge_page_refcount(struct page *page)
 1577 {
 1578         int i;
 1579         struct zone *zone = page_zone(page);
 1580         struct lruvec *lruvec;
 1581         int tail_count = 0;
 1582 
 1583         /* prevent PageLRU to go away from under us, and freeze lru stats */
 1584         spin_lock_irq(&zone->lru_lock);
 1585         lruvec = mem_cgroup_page_lruvec(page, zone);
 1586 
 1587         compound_lock(page);
 1588         /* complete memcg works before add pages to LRU */
 1589         mem_cgroup_split_huge_fixup(page);
 1590 
 1591         for (i = HPAGE_PMD_NR - 1; i >= 1; i--) {
 1592                 struct page *page_tail = page + i;
 1593 
 1594                 /* tail_page->_mapcount cannot change */
 1595                 BUG_ON(page_mapcount(page_tail) < 0);
 1596                 tail_count += page_mapcount(page_tail);
 1597                 /* check for overflow */
 1598                 BUG_ON(tail_count < 0);
 1599                 BUG_ON(atomic_read(&page_tail->_count) != 0);
 1600                 /*
 1601                  * tail_page->_count is zero and not changing from
 1602                  * under us. But get_page_unless_zero() may be running
 1603                  * from under us on the tail_page. If we used
 1604                  * atomic_set() below instead of atomic_add(), we
 1605                  * would then run atomic_set() concurrently with
 1606                  * get_page_unless_zero(), and atomic_set() is
 1607                  * implemented in C not using locked ops. spin_unlock
 1608                  * on x86 sometime uses locked ops because of PPro
 1609                  * errata 66, 92, so unless somebody can guarantee
 1610                  * atomic_set() here would be safe on all archs (and
 1611                  * not only on x86), it's safer to use atomic_add().
 1612                  */
 1613                 atomic_add(page_mapcount(page) + page_mapcount(page_tail) + 1,
 1614                            &page_tail->_count);
 1615 
 1616                 /* after clearing PageTail the gup refcount can be released */
 1617                 smp_mb();
 1618 
 1619                 /*
 1620                  * retain hwpoison flag of the poisoned tail page:
 1621                  *   fix for the unsuitable process killed on Guest Machine(KVM)
 1622                  *   by the memory-failure.
 1623                  */
 1624                 page_tail->flags &= ~PAGE_FLAGS_CHECK_AT_PREP | __PG_HWPOISON;
 1625                 page_tail->flags |= (page->flags &
 1626                                      ((1L << PG_referenced) |
 1627                                       (1L << PG_swapbacked) |
 1628                                       (1L << PG_mlocked) |
 1629                                       (1L << PG_uptodate)));
 1630                 page_tail->flags |= (1L << PG_dirty);
 1631 
 1632                 /* clear PageTail before overwriting first_page */
 1633                 smp_wmb();
 1634 
 1635                 /*
 1636                  * __split_huge_page_splitting() already set the
 1637                  * splitting bit in all pmd that could map this
 1638                  * hugepage, that will ensure no CPU can alter the
 1639                  * mapcount on the head page. The mapcount is only
 1640                  * accounted in the head page and it has to be
 1641                  * transferred to all tail pages in the below code. So
 1642                  * for this code to be safe, the split the mapcount
 1643                  * can't change. But that doesn't mean userland can't
 1644                  * keep changing and reading the page contents while
 1645                  * we transfer the mapcount, so the pmd splitting
 1646                  * status is achieved setting a reserved bit in the
 1647                  * pmd, not by clearing the present bit.
 1648                 */
 1649                 page_tail->_mapcount = page->_mapcount;
 1650 
 1651                 BUG_ON(page_tail->mapping);
 1652                 page_tail->mapping = page->mapping;
 1653 
 1654                 page_tail->index = page->index + i;
 1655                 page_xchg_last_nid(page_tail, page_last_nid(page));
 1656 
 1657                 BUG_ON(!PageAnon(page_tail));
 1658                 BUG_ON(!PageUptodate(page_tail));
 1659                 BUG_ON(!PageDirty(page_tail));
 1660                 BUG_ON(!PageSwapBacked(page_tail));
 1661 
 1662                 lru_add_page_tail(page, page_tail, lruvec);
 1663         }
 1664         atomic_sub(tail_count, &page->_count);
 1665         BUG_ON(atomic_read(&page->_count) <= 0);
 1666 
 1667         __mod_zone_page_state(zone, NR_ANON_TRANSPARENT_HUGEPAGES, -1);
 1668         __mod_zone_page_state(zone, NR_ANON_PAGES, HPAGE_PMD_NR);
 1669 
 1670         ClearPageCompound(page);
 1671         compound_unlock(page);
 1672         spin_unlock_irq(&zone->lru_lock);
 1673 
 1674         for (i = 1; i < HPAGE_PMD_NR; i++) {
 1675                 struct page *page_tail = page + i;
 1676                 BUG_ON(page_count(page_tail) <= 0);
 1677                 /*
 1678                  * Tail pages may be freed if there wasn't any mapping
 1679                  * like if add_to_swap() is running on a lru page that
 1680                  * had its mapping zapped. And freeing these pages
 1681                  * requires taking the lru_lock so we do the put_page
 1682                  * of the tail pages after the split is complete.
 1683                  */
 1684                 put_page(page_tail);
 1685         }
 1686 
 1687         /*
 1688          * Only the head page (now become a regular page) is required
 1689          * to be pinned by the caller.
 1690          */
 1691         BUG_ON(page_count(page) <= 0);
 1692 }
 1693 
 1694 static int __split_huge_page_map(struct page *page,
 1695                                  struct vm_area_struct *vma,
 1696                                  unsigned long address)
 1697 {
 1698         struct mm_struct *mm = vma->vm_mm;
 1699         pmd_t *pmd, _pmd;
 1700         int ret = 0, i;
 1701         pgtable_t pgtable;
 1702         unsigned long haddr;
 1703 
 1704         spin_lock(&mm->page_table_lock);
 1705         pmd = page_check_address_pmd(page, mm, address,
 1706                                      PAGE_CHECK_ADDRESS_PMD_SPLITTING_FLAG);
 1707         if (pmd) {
 1708                 pgtable = pgtable_trans_huge_withdraw(mm);
 1709                 pmd_populate(mm, &_pmd, pgtable);
 1710 
 1711                 haddr = address;
 1712                 for (i = 0; i < HPAGE_PMD_NR; i++, haddr += PAGE_SIZE) {
 1713                         pte_t *pte, entry;
 1714                         BUG_ON(PageCompound(page+i));
 1715                         entry = mk_pte(page + i, vma->vm_page_prot);
 1716                         entry = maybe_mkwrite(pte_mkdirty(entry), vma);
 1717                         if (!pmd_write(*pmd))
 1718                                 entry = pte_wrprotect(entry);
 1719                         else
 1720                                 BUG_ON(page_mapcount(page) != 1);
 1721                         if (!pmd_young(*pmd))
 1722                                 entry = pte_mkold(entry);
 1723                         if (pmd_numa(*pmd))
 1724                                 entry = pte_mknuma(entry);
 1725                         pte = pte_offset_map(&_pmd, haddr);
 1726                         BUG_ON(!pte_none(*pte));
 1727                         set_pte_at(mm, haddr, pte, entry);
 1728                         pte_unmap(pte);
 1729                 }
 1730 
 1731                 smp_wmb(); /* make pte visible before pmd */
 1732                 /*
 1733                  * Up to this point the pmd is present and huge and
 1734                  * userland has the whole access to the hugepage
 1735                  * during the split (which happens in place). If we
 1736                  * overwrite the pmd with the not-huge version
 1737                  * pointing to the pte here (which of course we could
 1738                  * if all CPUs were bug free), userland could trigger
 1739                  * a small page size TLB miss on the small sized TLB
 1740                  * while the hugepage TLB entry is still established
 1741                  * in the huge TLB. Some CPU doesn't like that. See
 1742                  * http://support.amd.com/us/Processor_TechDocs/41322.pdf,
 1743                  * Erratum 383 on page 93. Intel should be safe but is
 1744                  * also warns that it's only safe if the permission
 1745                  * and cache attributes of the two entries loaded in
 1746                  * the two TLB is identical (which should be the case
 1747                  * here). But it is generally safer to never allow
 1748                  * small and huge TLB entries for the same virtual
 1749                  * address to be loaded simultaneously. So instead of
 1750                  * doing "pmd_populate(); flush_tlb_range();" we first
 1751                  * mark the current pmd notpresent (atomically because
 1752                  * here the pmd_trans_huge and pmd_trans_splitting
 1753                  * must remain set at all times on the pmd until the
 1754                  * split is complete for this pmd), then we flush the
 1755                  * SMP TLB and finally we write the non-huge version
 1756                  * of the pmd entry with pmd_populate.
 1757                  */
 1758                 pmdp_invalidate(vma, address, pmd);
 1759                 pmd_populate(mm, pmd, pgtable);
 1760                 ret = 1;
 1761         }
 1762         spin_unlock(&mm->page_table_lock);
 1763 
 1764         return ret;
 1765 }
 1766 
 1767 /* must be called with anon_vma->root->rwsem held */
 1768 static void __split_huge_page(struct page *page,
 1769                               struct anon_vma *anon_vma)
 1770 {
 1771         int mapcount, mapcount2;
 1772         pgoff_t pgoff = page->index << (PAGE_CACHE_SHIFT - PAGE_SHIFT);
 1773         struct anon_vma_chain *avc;
 1774 
 1775         BUG_ON(!PageHead(page));
 1776         BUG_ON(PageTail(page));
 1777 
 1778         mapcount = 0;
 1779         anon_vma_interval_tree_foreach(avc, &anon_vma->rb_root, pgoff, pgoff) {
 1780                 struct vm_area_struct *vma = avc->vma;
 1781                 unsigned long addr = vma_address(page, vma);
 1782                 BUG_ON(is_vma_temporary_stack(vma));
 1783                 mapcount += __split_huge_page_splitting(page, vma, addr);
 1784         }
 1785         /*
 1786          * It is critical that new vmas are added to the tail of the
 1787          * anon_vma list. This guarantes that if copy_huge_pmd() runs
 1788          * and establishes a child pmd before
 1789          * __split_huge_page_splitting() freezes the parent pmd (so if
 1790          * we fail to prevent copy_huge_pmd() from running until the
 1791          * whole __split_huge_page() is complete), we will still see
 1792          * the newly established pmd of the child later during the
 1793          * walk, to be able to set it as pmd_trans_splitting too.
 1794          */
 1795         if (mapcount != page_mapcount(page))
 1796                 printk(KERN_ERR "mapcount %d page_mapcount %d\n",
 1797                        mapcount, page_mapcount(page));
 1798         BUG_ON(mapcount != page_mapcount(page));
 1799 
 1800         __split_huge_page_refcount(page);
 1801 
 1802         mapcount2 = 0;
 1803         anon_vma_interval_tree_foreach(avc, &anon_vma->rb_root, pgoff, pgoff) {
 1804                 struct vm_area_struct *vma = avc->vma;
 1805                 unsigned long addr = vma_address(page, vma);
 1806                 BUG_ON(is_vma_temporary_stack(vma));
 1807                 mapcount2 += __split_huge_page_map(page, vma, addr);
 1808         }
 1809         if (mapcount != mapcount2)
 1810                 printk(KERN_ERR "mapcount %d mapcount2 %d page_mapcount %d\n",
 1811                        mapcount, mapcount2, page_mapcount(page));
 1812         BUG_ON(mapcount != mapcount2);
 1813 }
 1814 
 1815 int split_huge_page(struct page *page)
 1816 {
 1817         struct anon_vma *anon_vma;
 1818         int ret = 1;
 1819 
 1820         BUG_ON(is_huge_zero_pfn(page_to_pfn(page)));
 1821         BUG_ON(!PageAnon(page));
 1822 
 1823         /*
 1824          * The caller does not necessarily hold an mmap_sem that would prevent
 1825          * the anon_vma disappearing so we first we take a reference to it
 1826          * and then lock the anon_vma for write. This is similar to
 1827          * page_lock_anon_vma_read except the write lock is taken to serialise
 1828          * against parallel split or collapse operations.
 1829          */
 1830         anon_vma = page_get_anon_vma(page);
 1831         if (!anon_vma)
 1832                 goto out;
 1833         anon_vma_lock_write(anon_vma);
 1834 
 1835         ret = 0;
 1836         if (!PageCompound(page))
 1837                 goto out_unlock;
 1838 
 1839         BUG_ON(!PageSwapBacked(page));
 1840         __split_huge_page(page, anon_vma);
 1841         count_vm_event(THP_SPLIT);
 1842 
 1843         BUG_ON(PageCompound(page));
 1844 out_unlock:
 1845         anon_vma_unlock(anon_vma);
 1846         put_anon_vma(anon_vma);
 1847 out:
 1848         return ret;
 1849 }
 1850 
 1851 #define VM_NO_THP (VM_SPECIAL|VM_MIXEDMAP|VM_HUGETLB|VM_SHARED|VM_MAYSHARE)
 1852 
 1853 int hugepage_madvise(struct vm_area_struct *vma,
 1854                      unsigned long *vm_flags, int advice)
 1855 {
 1856         struct mm_struct *mm = vma->vm_mm;
 1857 
 1858         switch (advice) {
 1859         case MADV_HUGEPAGE:
 1860                 /*
 1861                  * Be somewhat over-protective like KSM for now!
 1862                  */
 1863                 if (*vm_flags & (VM_HUGEPAGE | VM_NO_THP))
 1864                         return -EINVAL;
 1865                 if (mm->def_flags & VM_NOHUGEPAGE)
 1866                         return -EINVAL;
 1867                 *vm_flags &= ~VM_NOHUGEPAGE;
 1868                 *vm_flags |= VM_HUGEPAGE;
 1869                 /*
 1870                  * If the vma become good for khugepaged to scan,
 1871                  * register it here without waiting a page fault that
 1872                  * may not happen any time soon.
 1873                  */
 1874                 if (unlikely(khugepaged_enter_vma_merge(vma)))
 1875                         return -ENOMEM;
 1876                 break;
 1877         case MADV_NOHUGEPAGE:
 1878                 /*
 1879                  * Be somewhat over-protective like KSM for now!
 1880                  */
 1881                 if (*vm_flags & (VM_NOHUGEPAGE | VM_NO_THP))
 1882                         return -EINVAL;
 1883                 *vm_flags &= ~VM_HUGEPAGE;
 1884                 *vm_flags |= VM_NOHUGEPAGE;
 1885                 /*
 1886                  * Setting VM_NOHUGEPAGE will prevent khugepaged from scanning
 1887                  * this vma even if we leave the mm registered in khugepaged if
 1888                  * it got registered before VM_NOHUGEPAGE was set.
 1889                  */
 1890                 break;
 1891         }
 1892 
 1893         return 0;
 1894 }
 1895 
 1896 static int __init khugepaged_slab_init(void)
 1897 {
 1898         mm_slot_cache = kmem_cache_create("khugepaged_mm_slot",
 1899                                           sizeof(struct mm_slot),
 1900                                           __alignof__(struct mm_slot), 0, NULL);
 1901         if (!mm_slot_cache)
 1902                 return -ENOMEM;
 1903 
 1904         return 0;
 1905 }
 1906 
 1907 static void __init khugepaged_slab_free(void)
 1908 {
 1909         kmem_cache_destroy(mm_slot_cache);
 1910         mm_slot_cache = NULL;
 1911 }
 1912 
 1913 static inline struct mm_slot *alloc_mm_slot(void)
 1914 {
 1915         if (!mm_slot_cache)     /* initialization failed */
 1916                 return NULL;
 1917         return kmem_cache_zalloc(mm_slot_cache, GFP_KERNEL);
 1918 }
 1919 
 1920 static inline void free_mm_slot(struct mm_slot *mm_slot)
 1921 {
 1922         kmem_cache_free(mm_slot_cache, mm_slot);
 1923 }
 1924 
 1925 static int __init mm_slots_hash_init(void)
 1926 {
 1927         mm_slots_hash = kzalloc(MM_SLOTS_HASH_HEADS * sizeof(struct hlist_head),
 1928                                 GFP_KERNEL);
 1929         if (!mm_slots_hash)
 1930                 return -ENOMEM;
 1931         return 0;
 1932 }
 1933 
 1934 #if 0
 1935 static void __init mm_slots_hash_free(void)
 1936 {
 1937         kfree(mm_slots_hash);
 1938         mm_slots_hash = NULL;
 1939 }
 1940 #endif
 1941 
 1942 static struct mm_slot *get_mm_slot(struct mm_struct *mm)
 1943 {
 1944         struct mm_slot *mm_slot;
 1945         struct hlist_head *bucket;
 1946         struct hlist_node *node;
 1947 
 1948         bucket = &mm_slots_hash[((unsigned long)mm / sizeof(struct mm_struct))
 1949                                 % MM_SLOTS_HASH_HEADS];
 1950         hlist_for_each_entry(mm_slot, node, bucket, hash) {
 1951                 if (mm == mm_slot->mm)
 1952                         return mm_slot;
 1953         }
 1954         return NULL;
 1955 }
 1956 
 1957 static void insert_to_mm_slots_hash(struct mm_struct *mm,
 1958                                     struct mm_slot *mm_slot)
 1959 {
 1960         struct hlist_head *bucket;
 1961 
 1962         bucket = &mm_slots_hash[((unsigned long)mm / sizeof(struct mm_struct))
 1963                                 % MM_SLOTS_HASH_HEADS];
 1964         mm_slot->mm = mm;
 1965         hlist_add_head(&mm_slot->hash, bucket);
 1966 }
 1967 
 1968 static inline int khugepaged_test_exit(struct mm_struct *mm)
 1969 {
 1970         return atomic_read(&mm->mm_users) == 0;
 1971 }
 1972 
 1973 int __khugepaged_enter(struct mm_struct *mm)
 1974 {
 1975         struct mm_slot *mm_slot;
 1976         int wakeup;
 1977 
 1978         mm_slot = alloc_mm_slot();
 1979         if (!mm_slot)
 1980                 return -ENOMEM;
 1981 
 1982         /* __khugepaged_exit() must not run from under us */
 1983         VM_BUG_ON(khugepaged_test_exit(mm));
 1984         if (unlikely(test_and_set_bit(MMF_VM_HUGEPAGE, &mm->flags))) {
 1985                 free_mm_slot(mm_slot);
 1986                 return 0;
 1987         }
 1988 
 1989         spin_lock(&khugepaged_mm_lock);
 1990         insert_to_mm_slots_hash(mm, mm_slot);
 1991         /*
 1992          * Insert just behind the scanning cursor, to let the area settle
 1993          * down a little.
 1994          */
 1995         wakeup = list_empty(&khugepaged_scan.mm_head);
 1996         list_add_tail(&mm_slot->mm_node, &khugepaged_scan.mm_head);
 1997         spin_unlock(&khugepaged_mm_lock);
 1998 
 1999         atomic_inc(&mm->mm_count);
 2000         if (wakeup)
 2001                 wake_up_interruptible(&khugepaged_wait);
 2002 
 2003         return 0;
 2004 }
 2005 
 2006 int khugepaged_enter_vma_merge(struct vm_area_struct *vma)
 2007 {
 2008         unsigned long hstart, hend;
 2009         if (!vma->anon_vma)
 2010                 /*
 2011                  * Not yet faulted in so we will register later in the
 2012                  * page fault if needed.
 2013                  */
 2014                 return 0;
 2015         if (vma->vm_ops)
 2016                 /* khugepaged not yet working on file or special mappings */
 2017                 return 0;
 2018         VM_BUG_ON(vma->vm_flags & VM_NO_THP);
 2019         hstart = (vma->vm_start + ~HPAGE_PMD_MASK) & HPAGE_PMD_MASK;
 2020         hend = vma->vm_end & HPAGE_PMD_MASK;
 2021         if (hstart < hend)
 2022                 return khugepaged_enter(vma);
 2023         return 0;
 2024 }
 2025 
 2026 void __khugepaged_exit(struct mm_struct *mm)
 2027 {
 2028         struct mm_slot *mm_slot;
 2029         int free = 0;
 2030 
 2031         spin_lock(&khugepaged_mm_lock);
 2032         mm_slot = get_mm_slot(mm);
 2033         if (mm_slot && khugepaged_scan.mm_slot != mm_slot) {
 2034                 hlist_del(&mm_slot->hash);
 2035                 list_del(&mm_slot->mm_node);
 2036                 free = 1;
 2037         }
 2038         spin_unlock(&khugepaged_mm_lock);
 2039 
 2040         if (free) {
 2041                 clear_bit(MMF_VM_HUGEPAGE, &mm->flags);
 2042                 free_mm_slot(mm_slot);
 2043                 mmdrop(mm);
 2044         } else if (mm_slot) {
 2045                 /*
 2046                  * This is required to serialize against
 2047                  * khugepaged_test_exit() (which is guaranteed to run
 2048                  * under mmap sem read mode). Stop here (after we
 2049                  * return all pagetables will be destroyed) until
 2050                  * khugepaged has finished working on the pagetables
 2051                  * under the mmap_sem.
 2052                  */
 2053                 down_write(&mm->mmap_sem);
 2054                 up_write(&mm->mmap_sem);
 2055         }
 2056 }
 2057 
 2058 static void release_pte_page(struct page *page)
 2059 {
 2060         /* 0 stands for page_is_file_cache(page) == false */
 2061         dec_zone_page_state(page, NR_ISOLATED_ANON + 0);
 2062         unlock_page(page);
 2063         putback_lru_page(page);
 2064 }
 2065 
 2066 static void release_pte_pages(pte_t *pte, pte_t *_pte)
 2067 {
 2068         while (--_pte >= pte) {
 2069                 pte_t pteval = *_pte;
 2070                 if (!pte_none(pteval))
 2071                         release_pte_page(pte_page(pteval));
 2072         }
 2073 }
 2074 
 2075 static int __collapse_huge_page_isolate(struct vm_area_struct *vma,
 2076                                         unsigned long address,
 2077                                         pte_t *pte)
 2078 {
 2079         struct page *page;
 2080         pte_t *_pte;
 2081         int referenced = 0, none = 0;
 2082         for (_pte = pte; _pte < pte+HPAGE_PMD_NR;
 2083              _pte++, address += PAGE_SIZE) {
 2084                 pte_t pteval = *_pte;
 2085                 if (pte_none(pteval)) {
 2086                         if (++none <= khugepaged_max_ptes_none)
 2087                                 continue;
 2088                         else
 2089                                 goto out;
 2090                 }
 2091                 if (!pte_present(pteval) || !pte_write(pteval))
 2092                         goto out;
 2093                 page = vm_normal_page(vma, address, pteval);
 2094                 if (unlikely(!page))
 2095                         goto out;
 2096 
 2097                 VM_BUG_ON(PageCompound(page));
 2098                 BUG_ON(!PageAnon(page));
 2099                 VM_BUG_ON(!PageSwapBacked(page));
 2100 
 2101                 /* cannot use mapcount: can't collapse if there's a gup pin */
 2102                 if (page_count(page) != 1)
 2103                         goto out;
 2104                 /*
 2105                  * We can do it before isolate_lru_page because the
 2106                  * page can't be freed from under us. NOTE: PG_lock
 2107                  * is needed to serialize against split_huge_page
 2108                  * when invoked from the VM.
 2109                  */
 2110                 if (!trylock_page(page))
 2111                         goto out;
 2112                 /*
 2113                  * Isolate the page to avoid collapsing an hugepage
 2114                  * currently in use by the VM.
 2115                  */
 2116                 if (isolate_lru_page(page)) {
 2117                         unlock_page(page);
 2118                         goto out;
 2119                 }
 2120                 /* 0 stands for page_is_file_cache(page) == false */
 2121                 inc_zone_page_state(page, NR_ISOLATED_ANON + 0);
 2122                 VM_BUG_ON(!PageLocked(page));
 2123                 VM_BUG_ON(PageLRU(page));
 2124 
 2125                 /* If there is no mapped pte young don't collapse the page */
 2126                 if (pte_young(pteval) || PageReferenced(page) ||
 2127                     mmu_notifier_test_young(vma->vm_mm, address))
 2128                         referenced = 1;
 2129         }
 2130         if (likely(referenced))
 2131                 return 1;
 2132 out:
 2133         release_pte_pages(pte, _pte);
 2134         return 0;
 2135 }
 2136 
 2137 static void __collapse_huge_page_copy(pte_t *pte, struct page *page,
 2138                                       struct vm_area_struct *vma,
 2139                                       unsigned long address,
 2140                                       spinlock_t *ptl)
 2141 {
 2142         pte_t *_pte;
 2143         for (_pte = pte; _pte < pte+HPAGE_PMD_NR; _pte++) {
 2144                 pte_t pteval = *_pte;
 2145                 struct page *src_page;
 2146 
 2147                 if (pte_none(pteval)) {
 2148                         clear_user_highpage(page, address);
 2149                         add_mm_counter(vma->vm_mm, MM_ANONPAGES, 1);
 2150                 } else {
 2151                         src_page = pte_page(pteval);
 2152                         copy_user_highpage(page, src_page, address, vma);
 2153                         VM_BUG_ON(page_mapcount(src_page) != 1);
 2154                         release_pte_page(src_page);
 2155                         /*
 2156                          * ptl mostly unnecessary, but preempt has to
 2157                          * be disabled to update the per-cpu stats
 2158                          * inside page_remove_rmap().
 2159                          */
 2160                         spin_lock(ptl);
 2161                         /*
 2162                          * paravirt calls inside pte_clear here are
 2163                          * superfluous.
 2164                          */
 2165                         pte_clear(vma->vm_mm, address, _pte);
 2166                         page_remove_rmap(src_page);
 2167                         spin_unlock(ptl);
 2168                         free_page_and_swap_cache(src_page);
 2169                 }
 2170 
 2171                 address += PAGE_SIZE;
 2172                 page++;
 2173         }
 2174 }
 2175 
 2176 static void khugepaged_alloc_sleep(void)
 2177 {
 2178         wait_event_freezable_timeout(khugepaged_wait, false,
 2179                         msecs_to_jiffies(khugepaged_alloc_sleep_millisecs));
 2180 }
 2181 
 2182 #ifdef CONFIG_NUMA
 2183 static bool khugepaged_prealloc_page(struct page **hpage, bool *wait)
 2184 {
 2185         if (IS_ERR(*hpage)) {
 2186                 if (!*wait)
 2187                         return false;
 2188 
 2189                 *wait = false;
 2190                 *hpage = NULL;
 2191                 khugepaged_alloc_sleep();
 2192         } else if (*hpage) {
 2193                 put_page(*hpage);
 2194                 *hpage = NULL;
 2195         }
 2196 
 2197         return true;
 2198 }
 2199 
 2200 static struct page
 2201 *khugepaged_alloc_page(struct page **hpage, struct mm_struct *mm,
 2202                        struct vm_area_struct *vma, unsigned long address,
 2203                        int node)
 2204 {
 2205         VM_BUG_ON(*hpage);
 2206         /*
 2207          * Allocate the page while the vma is still valid and under
 2208          * the mmap_sem read mode so there is no memory allocation
 2209          * later when we take the mmap_sem in write mode. This is more
 2210          * friendly behavior (OTOH it may actually hide bugs) to
 2211          * filesystems in userland with daemons allocating memory in
 2212          * the userland I/O paths.  Allocating memory with the
 2213          * mmap_sem in read mode is good idea also to allow greater
 2214          * scalability.
 2215          */
 2216         *hpage  = alloc_hugepage_vma(khugepaged_defrag(), vma, address,
 2217                                       node, __GFP_OTHER_NODE);
 2218 
 2219         /*
 2220          * After allocating the hugepage, release the mmap_sem read lock in
 2221          * preparation for taking it in write mode.
 2222          */
 2223         up_read(&mm->mmap_sem);
 2224         if (unlikely(!*hpage)) {
 2225                 count_vm_event(THP_COLLAPSE_ALLOC_FAILED);
 2226                 *hpage = ERR_PTR(-ENOMEM);
 2227                 return NULL;
 2228         }
 2229 
 2230         count_vm_event(THP_COLLAPSE_ALLOC);
 2231         return *hpage;
 2232 }
 2233 #else
 2234 static struct page *khugepaged_alloc_hugepage(bool *wait)
 2235 {
 2236         struct page *hpage;
 2237 
 2238         do {
 2239                 hpage = alloc_hugepage(khugepaged_defrag());
 2240                 if (!hpage) {
 2241                         count_vm_event(THP_COLLAPSE_ALLOC_FAILED);
 2242                         if (!*wait)
 2243                                 return NULL;
 2244 
 2245                         *wait = false;
 2246                         khugepaged_alloc_sleep();
 2247                 } else
 2248                         count_vm_event(THP_COLLAPSE_ALLOC);
 2249         } while (unlikely(!hpage) && likely(khugepaged_enabled()));
 2250 
 2251         return hpage;
 2252 }
 2253 
 2254 static bool khugepaged_prealloc_page(struct page **hpage, bool *wait)
 2255 {
 2256         if (!*hpage)
 2257                 *hpage = khugepaged_alloc_hugepage(wait);
 2258 
 2259         if (unlikely(!*hpage))
 2260                 return false;
 2261 
 2262         return true;
 2263 }
 2264 
 2265 static struct page
 2266 *khugepaged_alloc_page(struct page **hpage, struct mm_struct *mm,
 2267                        struct vm_area_struct *vma, unsigned long address,
 2268                        int node)
 2269 {
 2270         up_read(&mm->mmap_sem);
 2271         VM_BUG_ON(!*hpage);
 2272         return  *hpage;
 2273 }
 2274 #endif
 2275 
 2276 static bool hugepage_vma_check(struct vm_area_struct *vma)
 2277 {
 2278         if ((!(vma->vm_flags & VM_HUGEPAGE) && !khugepaged_always()) ||
 2279             (vma->vm_flags & VM_NOHUGEPAGE))
 2280                 return false;
 2281 
 2282         if (!vma->anon_vma || vma->vm_ops)
 2283                 return false;
 2284         if (is_vma_temporary_stack(vma))
 2285                 return false;
 2286         VM_BUG_ON(vma->vm_flags & VM_NO_THP);
 2287         return true;
 2288 }
 2289 
 2290 static void collapse_huge_page(struct mm_struct *mm,
 2291                                    unsigned long address,
 2292                                    struct page **hpage,
 2293                                    struct vm_area_struct *vma,
 2294                                    int node)
 2295 {
 2296         pmd_t *pmd, _pmd;
 2297         pte_t *pte;
 2298         pgtable_t pgtable;
 2299         struct page *new_page;
 2300         spinlock_t *ptl;
 2301         int isolated;
 2302         unsigned long hstart, hend;
 2303         unsigned long mmun_start;       /* For mmu_notifiers */
 2304         unsigned long mmun_end;         /* For mmu_notifiers */
 2305 
 2306         VM_BUG_ON(address & ~HPAGE_PMD_MASK);
 2307 
 2308         /* release the mmap_sem read lock. */
 2309         new_page = khugepaged_alloc_page(hpage, mm, vma, address, node);
 2310         if (!new_page)
 2311                 return;
 2312 
 2313         if (unlikely(mem_cgroup_newpage_charge(new_page, mm, GFP_KERNEL)))
 2314                 return;
 2315 
 2316         /*
 2317          * Prevent all access to pagetables with the exception of
 2318          * gup_fast later hanlded by the ptep_clear_flush and the VM
 2319          * handled by the anon_vma lock + PG_lock.
 2320          */
 2321         down_write(&mm->mmap_sem);
 2322         if (unlikely(khugepaged_test_exit(mm)))
 2323                 goto out;
 2324 
 2325         vma = find_vma(mm, address);
 2326         hstart = (vma->vm_start + ~HPAGE_PMD_MASK) & HPAGE_PMD_MASK;
 2327         hend = vma->vm_end & HPAGE_PMD_MASK;
 2328         if (address < hstart || address + HPAGE_PMD_SIZE > hend)
 2329                 goto out;
 2330         if (!hugepage_vma_check(vma))
 2331                 goto out;
 2332         pmd = mm_find_pmd(mm, address);
 2333         if (!pmd)
 2334                 goto out;
 2335         if (pmd_trans_huge(*pmd))
 2336                 goto out;
 2337 
 2338         anon_vma_lock_write(vma->anon_vma);
 2339 
 2340         pte = pte_offset_map(pmd, address);
 2341         ptl = pte_lockptr(mm, pmd);
 2342 
 2343         mmun_start = address;
 2344         mmun_end   = address + HPAGE_PMD_SIZE;
 2345         mmu_notifier_invalidate_range_start(mm, mmun_start, mmun_end);
 2346         spin_lock(&mm->page_table_lock); /* probably unnecessary */
 2347         /*
 2348          * After this gup_fast can't run anymore. This also removes
 2349          * any huge TLB entry from the CPU so we won't allow
 2350          * huge and small TLB entries for the same virtual address
 2351          * to avoid the risk of CPU bugs in that area.
 2352          */
 2353         _pmd = pmdp_clear_flush(vma, address, pmd);
 2354         spin_unlock(&mm->page_table_lock);
 2355         mmu_notifier_invalidate_range_end(mm, mmun_start, mmun_end);
 2356 
 2357         spin_lock(ptl);
 2358         isolated = __collapse_huge_page_isolate(vma, address, pte);
 2359         spin_unlock(ptl);
 2360 
 2361         if (unlikely(!isolated)) {
 2362                 pte_unmap(pte);
 2363                 spin_lock(&mm->page_table_lock);
 2364                 BUG_ON(!pmd_none(*pmd));
 2365                 set_pmd_at(mm, address, pmd, _pmd);
 2366                 spin_unlock(&mm->page_table_lock);
 2367                 anon_vma_unlock(vma->anon_vma);
 2368                 goto out;
 2369         }
 2370 
 2371         /*
 2372          * All pages are isolated and locked so anon_vma rmap
 2373          * can't run anymore.
 2374          */
 2375         anon_vma_unlock(vma->anon_vma);
 2376 
 2377         __collapse_huge_page_copy(pte, new_page, vma, address, ptl);
 2378         pte_unmap(pte);
 2379         __SetPageUptodate(new_page);
 2380         pgtable = pmd_pgtable(_pmd);
 2381 
 2382         _pmd = mk_huge_pmd(new_page, vma);
 2383 
 2384         /*
 2385          * spin_lock() below is not the equivalent of smp_wmb(), so
 2386          * this is needed to avoid the copy_huge_page writes to become
 2387          * visible after the set_pmd_at() write.
 2388          */
 2389         smp_wmb();
 2390 
 2391         spin_lock(&mm->page_table_lock);
 2392         BUG_ON(!pmd_none(*pmd));
 2393         page_add_new_anon_rmap(new_page, vma, address);
 2394         set_pmd_at(mm, address, pmd, _pmd);
 2395         update_mmu_cache_pmd(vma, address, pmd);
 2396         pgtable_trans_huge_deposit(mm, pgtable);
 2397         spin_unlock(&mm->page_table_lock);
 2398 
 2399         *hpage = NULL;
 2400 
 2401         khugepaged_pages_collapsed++;
 2402 out_up_write:
 2403         up_write(&mm->mmap_sem);
 2404         return;
 2405 
 2406 out:
 2407         mem_cgroup_uncharge_page(new_page);
 2408         goto out_up_write;
 2409 }
 2410 
 2411 static int khugepaged_scan_pmd(struct mm_struct *mm,
 2412                                struct vm_area_struct *vma,
 2413                                unsigned long address,
 2414                                struct page **hpage)
 2415 {
 2416         pmd_t *pmd;
 2417         pte_t *pte, *_pte;
 2418         int ret = 0, referenced = 0, none = 0;
 2419         struct page *page;
 2420         unsigned long _address;
 2421         spinlock_t *ptl;
 2422         int node = -1;
 2423 
 2424         VM_BUG_ON(address & ~HPAGE_PMD_MASK);
 2425 
 2426         pmd = mm_find_pmd(mm, address);
 2427         if (!pmd)
 2428                 goto out;
 2429         if (pmd_trans_huge(*pmd))
 2430                 goto out;
 2431 
 2432         pte = pte_offset_map_lock(mm, pmd, address, &ptl);
 2433         for (_address = address, _pte = pte; _pte < pte+HPAGE_PMD_NR;
 2434              _pte++, _address += PAGE_SIZE) {
 2435                 pte_t pteval = *_pte;
 2436                 if (pte_none(pteval)) {
 2437                         if (++none <= khugepaged_max_ptes_none)
 2438                                 continue;
 2439                         else
 2440                                 goto out_unmap;
 2441                 }
 2442                 if (!pte_present(pteval) || !pte_write(pteval))
 2443                         goto out_unmap;
 2444                 page = vm_normal_page(vma, _address, pteval);
 2445                 if (unlikely(!page))
 2446                         goto out_unmap;
 2447                 /*
 2448                  * Chose the node of the first page. This could
 2449                  * be more sophisticated and look at more pages,
 2450                  * but isn't for now.
 2451                  */
 2452                 if (node == -1)
 2453                         node = page_to_nid(page);
 2454                 VM_BUG_ON(PageCompound(page));
 2455                 if (!PageLRU(page) || PageLocked(page) || !PageAnon(page))
 2456                         goto out_unmap;
 2457                 /* cannot use mapcount: can't collapse if there's a gup pin */
 2458                 if (page_count(page) != 1)
 2459                         goto out_unmap;
 2460                 if (pte_young(pteval) || PageReferenced(page) ||
 2461                     mmu_notifier_test_young(vma->vm_mm, address))
 2462                         referenced = 1;
 2463         }
 2464         if (referenced)
 2465                 ret = 1;
 2466 out_unmap:
 2467         pte_unmap_unlock(pte, ptl);
 2468         if (ret)
 2469                 /* collapse_huge_page will return with the mmap_sem released */
 2470                 collapse_huge_page(mm, address, hpage, vma, node);
 2471 out:
 2472         return ret;
 2473 }
 2474 
 2475 static void collect_mm_slot(struct mm_slot *mm_slot)
 2476 {
 2477         struct mm_struct *mm = mm_slot->mm;
 2478 
 2479         VM_BUG_ON(NR_CPUS != 1 && !spin_is_locked(&khugepaged_mm_lock));
 2480 
 2481         if (khugepaged_test_exit(mm)) {
 2482                 /* free mm_slot */
 2483                 hlist_del(&mm_slot->hash);
 2484                 list_del(&mm_slot->mm_node);
 2485 
 2486                 /*
 2487                  * Not strictly needed because the mm exited already.
 2488                  *
 2489                  * clear_bit(MMF_VM_HUGEPAGE, &mm->flags);
 2490                  */
 2491 
 2492                 /* khugepaged_mm_lock actually not necessary for the below */
 2493                 free_mm_slot(mm_slot);
 2494                 mmdrop(mm);
 2495         }
 2496 }
 2497 
 2498 static unsigned int khugepaged_scan_mm_slot(unsigned int pages,
 2499                                             struct page **hpage)
 2500         __releases(&khugepaged_mm_lock)
 2501         __acquires(&khugepaged_mm_lock)
 2502 {
 2503         struct mm_slot *mm_slot;
 2504         struct mm_struct *mm;
 2505         struct vm_area_struct *vma;
 2506         int progress = 0;
 2507 
 2508         VM_BUG_ON(!pages);
 2509         VM_BUG_ON(NR_CPUS != 1 && !spin_is_locked(&khugepaged_mm_lock));
 2510 
 2511         if (khugepaged_scan.mm_slot)
 2512                 mm_slot = khugepaged_scan.mm_slot;
 2513         else {
 2514                 mm_slot = list_entry(khugepaged_scan.mm_head.next,
 2515                                      struct mm_slot, mm_node);
 2516                 khugepaged_scan.address = 0;
 2517                 khugepaged_scan.mm_slot = mm_slot;
 2518         }
 2519         spin_unlock(&khugepaged_mm_lock);
 2520 
 2521         mm = mm_slot->mm;
 2522         down_read(&mm->mmap_sem);
 2523         if (unlikely(khugepaged_test_exit(mm)))
 2524                 vma = NULL;
 2525         else
 2526                 vma = find_vma(mm, khugepaged_scan.address);
 2527 
 2528         progress++;
 2529         for (; vma; vma = vma->vm_next) {
 2530                 unsigned long hstart, hend;
 2531 
 2532                 cond_resched();
 2533                 if (unlikely(khugepaged_test_exit(mm))) {
 2534                         progress++;
 2535                         break;
 2536                 }
 2537                 if (!hugepage_vma_check(vma)) {
 2538 skip:
 2539                         progress++;
 2540                         continue;
 2541                 }
 2542                 hstart = (vma->vm_start + ~HPAGE_PMD_MASK) & HPAGE_PMD_MASK;
 2543                 hend = vma->vm_end & HPAGE_PMD_MASK;
 2544                 if (hstart >= hend)
 2545                         goto skip;
 2546                 if (khugepaged_scan.address > hend)
 2547                         goto skip;
 2548                 if (khugepaged_scan.address < hstart)
 2549                         khugepaged_scan.address = hstart;
 2550                 VM_BUG_ON(khugepaged_scan.address & ~HPAGE_PMD_MASK);
 2551 
 2552                 while (khugepaged_scan.address < hend) {
 2553                         int ret;
 2554                         cond_resched();
 2555                         if (unlikely(khugepaged_test_exit(mm)))
 2556                                 goto breakouterloop;
 2557 
 2558                         VM_BUG_ON(khugepaged_scan.address < hstart ||
 2559                                   khugepaged_scan.address + HPAGE_PMD_SIZE >
 2560                                   hend);
 2561                         ret = khugepaged_scan_pmd(mm, vma,
 2562                                                   khugepaged_scan.address,
 2563                                                   hpage);
 2564                         /* move to next address */
 2565                         khugepaged_scan.address += HPAGE_PMD_SIZE;
 2566                         progress += HPAGE_PMD_NR;
 2567                         if (ret)
 2568                                 /* we released mmap_sem so break loop */
 2569                                 goto breakouterloop_mmap_sem;
 2570                         if (progress >= pages)
 2571                                 goto breakouterloop;
 2572                 }
 2573         }
 2574 breakouterloop:
 2575         up_read(&mm->mmap_sem); /* exit_mmap will destroy ptes after this */
 2576 breakouterloop_mmap_sem:
 2577 
 2578         spin_lock(&khugepaged_mm_lock);
 2579         VM_BUG_ON(khugepaged_scan.mm_slot != mm_slot);
 2580         /*
 2581          * Release the current mm_slot if this mm is about to die, or
 2582          * if we scanned all vmas of this mm.
 2583          */
 2584         if (khugepaged_test_exit(mm) || !vma) {
 2585                 /*
 2586                  * Make sure that if mm_users is reaching zero while
 2587                  * khugepaged runs here, khugepaged_exit will find
 2588                  * mm_slot not pointing to the exiting mm.
 2589                  */
 2590                 if (mm_slot->mm_node.next != &khugepaged_scan.mm_head) {
 2591                         khugepaged_scan.mm_slot = list_entry(
 2592                                 mm_slot->mm_node.next,
 2593                                 struct mm_slot, mm_node);
 2594                         khugepaged_scan.address = 0;
 2595                 } else {
 2596                         khugepaged_scan.mm_slot = NULL;
 2597                         khugepaged_full_scans++;
 2598                 }
 2599 
 2600                 collect_mm_slot(mm_slot);
 2601         }
 2602 
 2603         return progress;
 2604 }
 2605 
 2606 static int khugepaged_has_work(void)
 2607 {
 2608         return !list_empty(&khugepaged_scan.mm_head) &&
 2609                 khugepaged_enabled();
 2610 }
 2611 
 2612 static int khugepaged_wait_event(void)
 2613 {
 2614         return !list_empty(&khugepaged_scan.mm_head) ||
 2615                 kthread_should_stop();
 2616 }
 2617 
 2618 static void khugepaged_do_scan(void)
 2619 {
 2620         struct page *hpage = NULL;
 2621         unsigned int progress = 0, pass_through_head = 0;
 2622         unsigned int pages = khugepaged_pages_to_scan;
 2623         bool wait = true;
 2624 
 2625         barrier(); /* write khugepaged_pages_to_scan to local stack */
 2626 
 2627         while (progress < pages) {
 2628                 if (!khugepaged_prealloc_page(&hpage, &wait))
 2629                         break;
 2630 
 2631                 cond_resched();
 2632 
 2633                 if (unlikely(kthread_should_stop() || freezing(current)))
 2634                         break;
 2635 
 2636                 spin_lock(&khugepaged_mm_lock);
 2637                 if (!khugepaged_scan.mm_slot)
 2638                         pass_through_head++;
 2639                 if (khugepaged_has_work() &&
 2640                     pass_through_head < 2)
 2641                         progress += khugepaged_scan_mm_slot(pages - progress,
 2642                                                             &hpage);
 2643                 else
 2644                         progress = pages;
 2645                 spin_unlock(&khugepaged_mm_lock);
 2646         }
 2647 
 2648         if (!IS_ERR_OR_NULL(hpage))
 2649                 put_page(hpage);
 2650 }
 2651 
 2652 static void khugepaged_wait_work(void)
 2653 {
 2654         try_to_freeze();
 2655 
 2656         if (khugepaged_has_work()) {
 2657                 if (!khugepaged_scan_sleep_millisecs)
 2658                         return;
 2659 
 2660                 wait_event_freezable_timeout(khugepaged_wait,
 2661                                              kthread_should_stop(),
 2662                         msecs_to_jiffies(khugepaged_scan_sleep_millisecs));
 2663                 return;
 2664         }
 2665 
 2666         if (khugepaged_enabled())
 2667                 wait_event_freezable(khugepaged_wait, khugepaged_wait_event());
 2668 }
 2669 
 2670 static int khugepaged(void *none)
 2671 {
 2672         struct mm_slot *mm_slot;
 2673 
 2674         set_freezable();
 2675         set_user_nice(current, 19);
 2676 
 2677         while (!kthread_should_stop()) {
 2678                 khugepaged_do_scan();
 2679                 khugepaged_wait_work();
 2680         }
 2681 
 2682         spin_lock(&khugepaged_mm_lock);
 2683         mm_slot = khugepaged_scan.mm_slot;
 2684         khugepaged_scan.mm_slot = NULL;
 2685         if (mm_slot)
 2686                 collect_mm_slot(mm_slot);
 2687         spin_unlock(&khugepaged_mm_lock);
 2688         return 0;
 2689 }
 2690 
 2691 static void __split_huge_zero_page_pmd(struct vm_area_struct *vma,
 2692                 unsigned long haddr, pmd_t *pmd)
 2693 {
 2694         struct mm_struct *mm = vma->vm_mm;
 2695         pgtable_t pgtable;
 2696         pmd_t _pmd;
 2697         int i;
 2698 
 2699         pmdp_clear_flush(vma, haddr, pmd);
 2700         /* leave pmd empty until pte is filled */
 2701 
 2702         pgtable = pgtable_trans_huge_withdraw(mm);
 2703         pmd_populate(mm, &_pmd, pgtable);
 2704 
 2705         for (i = 0; i < HPAGE_PMD_NR; i++, haddr += PAGE_SIZE) {
 2706                 pte_t *pte, entry;
 2707                 entry = pfn_pte(my_zero_pfn(haddr), vma->vm_page_prot);
 2708                 entry = pte_mkspecial(entry);
 2709                 pte = pte_offset_map(&_pmd, haddr);
 2710                 VM_BUG_ON(!pte_none(*pte));
 2711                 set_pte_at(mm, haddr, pte, entry);
 2712                 pte_unmap(pte);
 2713         }
 2714         smp_wmb(); /* make pte visible before pmd */
 2715         pmd_populate(mm, pmd, pgtable);
 2716         put_huge_zero_page();
 2717 }
 2718 
 2719 void __split_huge_page_pmd(struct vm_area_struct *vma, unsigned long address,
 2720                 pmd_t *pmd)
 2721 {
 2722         struct page *page;
 2723         struct mm_struct *mm = vma->vm_mm;
 2724         unsigned long haddr = address & HPAGE_PMD_MASK;
 2725         unsigned long mmun_start;       /* For mmu_notifiers */
 2726         unsigned long mmun_end;         /* For mmu_notifiers */
 2727 
 2728         BUG_ON(vma->vm_start > haddr || vma->vm_end < haddr + HPAGE_PMD_SIZE);
 2729 
 2730         mmun_start = haddr;
 2731         mmun_end   = haddr + HPAGE_PMD_SIZE;
 2732         mmu_notifier_invalidate_range_start(mm, mmun_start, mmun_end);
 2733         spin_lock(&mm->page_table_lock);
 2734         if (unlikely(!pmd_trans_huge(*pmd))) {
 2735                 spin_unlock(&mm->page_table_lock);
 2736                 mmu_notifier_invalidate_range_end(mm, mmun_start, mmun_end);
 2737                 return;
 2738         }
 2739         if (is_huge_zero_pmd(*pmd)) {
 2740                 __split_huge_zero_page_pmd(vma, haddr, pmd);
 2741                 spin_unlock(&mm->page_table_lock);
 2742                 mmu_notifier_invalidate_range_end(mm, mmun_start, mmun_end);
 2743                 return;
 2744         }
 2745         page = pmd_page(*pmd);
 2746         VM_BUG_ON(!page_count(page));
 2747         get_page(page);
 2748         spin_unlock(&mm->page_table_lock);
 2749         mmu_notifier_invalidate_range_end(mm, mmun_start, mmun_end);
 2750 
 2751         split_huge_page(page);
 2752 
 2753         put_page(page);
 2754         BUG_ON(pmd_trans_huge(*pmd));
 2755 }
 2756 
 2757 void split_huge_page_pmd_mm(struct mm_struct *mm, unsigned long address,
 2758                 pmd_t *pmd)
 2759 {
 2760         struct vm_area_struct *vma;
 2761 
 2762         vma = find_vma(mm, address);
 2763         BUG_ON(vma == NULL);
 2764         split_huge_page_pmd(vma, address, pmd);
 2765 }
 2766 
 2767 static void split_huge_page_address(struct mm_struct *mm,
 2768                                     unsigned long address)
 2769 {
 2770         pmd_t *pmd;
 2771 
 2772         VM_BUG_ON(!(address & ~HPAGE_PMD_MASK));
 2773 
 2774         pmd = mm_find_pmd(mm, address);
 2775         if (!pmd)
 2776                 return;
 2777         /*
 2778          * Caller holds the mmap_sem write mode, so a huge pmd cannot
 2779          * materialize from under us.
 2780          */
 2781         split_huge_page_pmd_mm(mm, address, pmd);
 2782 }
 2783 
 2784 void __vma_adjust_trans_huge(struct vm_area_struct *vma,
 2785                              unsigned long start,
 2786                              unsigned long end,
 2787                              long adjust_next)
 2788 {
 2789         /*
 2790          * If the new start address isn't hpage aligned and it could
 2791          * previously contain an hugepage: check if we need to split
 2792          * an huge pmd.
 2793          */
 2794         if (start & ~HPAGE_PMD_MASK &&
 2795             (start & HPAGE_PMD_MASK) >= vma->vm_start &&
 2796             (start & HPAGE_PMD_MASK) + HPAGE_PMD_SIZE <= vma->vm_end)
 2797                 split_huge_page_address(vma->vm_mm, start);
 2798 
 2799         /*
 2800          * If the new end address isn't hpage aligned and it could
 2801          * previously contain an hugepage: check if we need to split
 2802          * an huge pmd.
 2803          */
 2804         if (end & ~HPAGE_PMD_MASK &&
 2805             (end & HPAGE_PMD_MASK) >= vma->vm_start &&
 2806             (end & HPAGE_PMD_MASK) + HPAGE_PMD_SIZE <= vma->vm_end)
 2807                 split_huge_page_address(vma->vm_mm, end);
 2808 
 2809         /*
 2810          * If we're also updating the vma->vm_next->vm_start, if the new
 2811          * vm_next->vm_start isn't page aligned and it could previously
 2812          * contain an hugepage: check if we need to split an huge pmd.
 2813          */
 2814         if (adjust_next > 0) {
 2815                 struct vm_area_struct *next = vma->vm_next;
 2816                 unsigned long nstart = next->vm_start;
 2817                 nstart += adjust_next << PAGE_SHIFT;
 2818                 if (nstart & ~HPAGE_PMD_MASK &&
 2819                     (nstart & HPAGE_PMD_MASK) >= next->vm_start &&
 2820                     (nstart & HPAGE_PMD_MASK) + HPAGE_PMD_SIZE <= next->vm_end)
 2821                         split_huge_page_address(next->vm_mm, nstart);
 2822         }
 2823 }

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