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

     /*
      * Generic hugetlb support.
      * (C) Nadia Yvette Chambers, April 2004
      */
     #include <linux/list.h>
     #include <linux/init.h>
     #include <linux/module.h>
     #include <linux/mm.h>
     #include <linux/seq_file.h>
    #include <linux/sysctl.h>
    #include <linux/highmem.h>
    #include <linux/mmu_notifier.h>
    #include <linux/nodemask.h>
    #include <linux/pagemap.h>
    #include <linux/mempolicy.h>
    #include <linux/cpuset.h>
    #include <linux/mutex.h>
    #include <linux/bootmem.h>
    #include <linux/sysfs.h>
    #include <linux/slab.h>
    #include <linux/rmap.h>
    #include <linux/swap.h>
    #include <linux/swapops.h>
    
    #include <asm/page.h>
    #include <asm/pgtable.h>
    #include <asm/tlb.h>
    
    #include <linux/io.h>
    #include <linux/hugetlb.h>
    #include <linux/hugetlb_cgroup.h>
    #include <linux/node.h>
    #include "internal.h"
    
    const unsigned long hugetlb_zero = 0, hugetlb_infinity = ~0UL;
    static gfp_t htlb_alloc_mask = GFP_HIGHUSER;
    unsigned long hugepages_treat_as_movable;
    
    int hugetlb_max_hstate __read_mostly;
    unsigned int default_hstate_idx;
    struct hstate hstates[HUGE_MAX_HSTATE];
    
    __initdata LIST_HEAD(huge_boot_pages);
    
    /* for command line parsing */
    static struct hstate * __initdata parsed_hstate;
    static unsigned long __initdata default_hstate_max_huge_pages;
    static unsigned long __initdata default_hstate_size;
    
    /*
     * Protects updates to hugepage_freelists, nr_huge_pages, and free_huge_pages
     */
    DEFINE_SPINLOCK(hugetlb_lock);
    
    static inline void unlock_or_release_subpool(struct hugepage_subpool *spool)
    {
            bool free = (spool->count == 0) && (spool->used_hpages == 0);
    
            spin_unlock(&spool->lock);
    
            /* If no pages are used, and no other handles to the subpool
             * remain, free the subpool the subpool remain */
            if (free)
                    kfree(spool);
    }
    
    struct hugepage_subpool *hugepage_new_subpool(long nr_blocks)
    {
            struct hugepage_subpool *spool;
    
            spool = kmalloc(sizeof(*spool), GFP_KERNEL);
            if (!spool)
                    return NULL;
    
            spin_lock_init(&spool->lock);
            spool->count = 1;
            spool->max_hpages = nr_blocks;
            spool->used_hpages = 0;
    
            return spool;
    }
    
    void hugepage_put_subpool(struct hugepage_subpool *spool)
    {
            spin_lock(&spool->lock);
            BUG_ON(!spool->count);
            spool->count--;
            unlock_or_release_subpool(spool);
    }
    
    static int hugepage_subpool_get_pages(struct hugepage_subpool *spool,
                                          long delta)
    {
            int ret = 0;
    
            if (!spool)
                    return 0;
    
            spin_lock(&spool->lock);
           if ((spool->used_hpages + delta) <= spool->max_hpages) {
                   spool->used_hpages += delta;
           } else {
                   ret = -ENOMEM;
           }
           spin_unlock(&spool->lock);
   
           return ret;
   }
   
   static void hugepage_subpool_put_pages(struct hugepage_subpool *spool,
                                          long delta)
   {
           if (!spool)
                   return;
   
           spin_lock(&spool->lock);
           spool->used_hpages -= delta;
           /* If hugetlbfs_put_super couldn't free spool due to
           * an outstanding quota reference, free it now. */
           unlock_or_release_subpool(spool);
   }
   
   static inline struct hugepage_subpool *subpool_inode(struct inode *inode)
   {
           return HUGETLBFS_SB(inode->i_sb)->spool;
   }
   
   static inline struct hugepage_subpool *subpool_vma(struct vm_area_struct *vma)
   {
           return subpool_inode(vma->vm_file->f_dentry->d_inode);
   }
   
   /*
    * Region tracking -- allows tracking of reservations and instantiated pages
    *                    across the pages in a mapping.
    *
    * The region data structures are protected by a combination of the mmap_sem
    * and the hugetlb_instantion_mutex.  To access or modify a region the caller
    * must either hold the mmap_sem for write, or the mmap_sem for read and
    * the hugetlb_instantiation mutex:
    *
    *      down_write(&mm->mmap_sem);
    * or
    *      down_read(&mm->mmap_sem);
    *      mutex_lock(&hugetlb_instantiation_mutex);
    */
   struct file_region {
           struct list_head link;
           long from;
           long to;
   };
   
   static long region_add(struct list_head *head, long f, long t)
   {
           struct file_region *rg, *nrg, *trg;
   
           /* Locate the region we are either in or before. */
           list_for_each_entry(rg, head, link)
                   if (f <= rg->to)
                           break;
   
           /* Round our left edge to the current segment if it encloses us. */
           if (f > rg->from)
                   f = rg->from;
   
           /* Check for and consume any regions we now overlap with. */
           nrg = rg;
           list_for_each_entry_safe(rg, trg, rg->link.prev, link) {
                   if (&rg->link == head)
                           break;
                   if (rg->from > t)
                           break;
   
                   /* If this area reaches higher then extend our area to
                    * include it completely.  If this is not the first area
                    * which we intend to reuse, free it. */
                   if (rg->to > t)
                           t = rg->to;
                   if (rg != nrg) {
                           list_del(&rg->link);
                           kfree(rg);
                   }
           }
           nrg->from = f;
           nrg->to = t;
           return 0;
   }
   
   static long region_chg(struct list_head *head, long f, long t)
   {
           struct file_region *rg, *nrg;
           long chg = 0;
   
           /* Locate the region we are before or in. */
           list_for_each_entry(rg, head, link)
                   if (f <= rg->to)
                           break;
   
           /* If we are below the current region then a new region is required.
            * Subtle, allocate a new region at the position but make it zero
            * size such that we can guarantee to record the reservation. */
           if (&rg->link == head || t < rg->from) {
                   nrg = kmalloc(sizeof(*nrg), GFP_KERNEL);
                   if (!nrg)
                           return -ENOMEM;
                   nrg->from = f;
                   nrg->to   = f;
                   INIT_LIST_HEAD(&nrg->link);
                   list_add(&nrg->link, rg->link.prev);
   
                   return t - f;
           }
   
           /* Round our left edge to the current segment if it encloses us. */
           if (f > rg->from)
                   f = rg->from;
           chg = t - f;
   
           /* Check for and consume any regions we now overlap with. */
           list_for_each_entry(rg, rg->link.prev, link) {
                   if (&rg->link == head)
                           break;
                   if (rg->from > t)
                           return chg;
   
                   /* We overlap with this area, if it extends further than
                    * us then we must extend ourselves.  Account for its
                    * existing reservation. */
                   if (rg->to > t) {
                           chg += rg->to - t;
                           t = rg->to;
                   }
                   chg -= rg->to - rg->from;
           }
           return chg;
   }
   
   static long region_truncate(struct list_head *head, long end)
   {
           struct file_region *rg, *trg;
           long chg = 0;
   
           /* Locate the region we are either in or before. */
           list_for_each_entry(rg, head, link)
                   if (end <= rg->to)
                           break;
           if (&rg->link == head)
                   return 0;
   
           /* If we are in the middle of a region then adjust it. */
           if (end > rg->from) {
                   chg = rg->to - end;
                   rg->to = end;
                   rg = list_entry(rg->link.next, typeof(*rg), link);
           }
   
           /* Drop any remaining regions. */
           list_for_each_entry_safe(rg, trg, rg->link.prev, link) {
                   if (&rg->link == head)
                           break;
                   chg += rg->to - rg->from;
                   list_del(&rg->link);
                   kfree(rg);
           }
           return chg;
   }
   
   static long region_count(struct list_head *head, long f, long t)
   {
           struct file_region *rg;
           long chg = 0;
   
           /* Locate each segment we overlap with, and count that overlap. */
           list_for_each_entry(rg, head, link) {
                   long seg_from;
                   long seg_to;
   
                   if (rg->to <= f)
                           continue;
                   if (rg->from >= t)
                           break;
   
                   seg_from = max(rg->from, f);
                   seg_to = min(rg->to, t);
   
                   chg += seg_to - seg_from;
           }
   
           return chg;
   }
   
   /*
    * Convert the address within this vma to the page offset within
    * the mapping, in pagecache page units; huge pages here.
    */
   static pgoff_t vma_hugecache_offset(struct hstate *h,
                           struct vm_area_struct *vma, unsigned long address)
   {
           return ((address - vma->vm_start) >> huge_page_shift(h)) +
                           (vma->vm_pgoff >> huge_page_order(h));
   }
   
   pgoff_t linear_hugepage_index(struct vm_area_struct *vma,
                                        unsigned long address)
   {
           return vma_hugecache_offset(hstate_vma(vma), vma, address);
   }
   
   /*
    * Return the size of the pages allocated when backing a VMA. In the majority
    * cases this will be same size as used by the page table entries.
    */
   unsigned long vma_kernel_pagesize(struct vm_area_struct *vma)
   {
           struct hstate *hstate;
   
           if (!is_vm_hugetlb_page(vma))
                   return PAGE_SIZE;
   
           hstate = hstate_vma(vma);
   
           return 1UL << (hstate->order + PAGE_SHIFT);
   }
   EXPORT_SYMBOL_GPL(vma_kernel_pagesize);
   
   /*
    * Return the page size being used by the MMU to back a VMA. In the majority
    * of cases, the page size used by the kernel matches the MMU size. On
    * architectures where it differs, an architecture-specific version of this
    * function is required.
    */
   #ifndef vma_mmu_pagesize
   unsigned long vma_mmu_pagesize(struct vm_area_struct *vma)
   {
           return vma_kernel_pagesize(vma);
   }
   #endif
   
   /*
    * Flags for MAP_PRIVATE reservations.  These are stored in the bottom
    * bits of the reservation map pointer, which are always clear due to
    * alignment.
    */
   #define HPAGE_RESV_OWNER    (1UL << 0)
   #define HPAGE_RESV_UNMAPPED (1UL << 1)
   #define HPAGE_RESV_MASK (HPAGE_RESV_OWNER | HPAGE_RESV_UNMAPPED)
   
   /*
    * These helpers are used to track how many pages are reserved for
    * faults in a MAP_PRIVATE mapping. Only the process that called mmap()
    * is guaranteed to have their future faults succeed.
    *
    * With the exception of reset_vma_resv_huge_pages() which is called at fork(),
    * the reserve counters are updated with the hugetlb_lock held. It is safe
    * to reset the VMA at fork() time as it is not in use yet and there is no
    * chance of the global counters getting corrupted as a result of the values.
    *
    * The private mapping reservation is represented in a subtly different
    * manner to a shared mapping.  A shared mapping has a region map associated
    * with the underlying file, this region map represents the backing file
    * pages which have ever had a reservation assigned which this persists even
    * after the page is instantiated.  A private mapping has a region map
    * associated with the original mmap which is attached to all VMAs which
    * reference it, this region map represents those offsets which have consumed
    * reservation ie. where pages have been instantiated.
    */
   static unsigned long get_vma_private_data(struct vm_area_struct *vma)
   {
           return (unsigned long)vma->vm_private_data;
   }
   
   static void set_vma_private_data(struct vm_area_struct *vma,
                                                           unsigned long value)
   {
           vma->vm_private_data = (void *)value;
   }
   
   struct resv_map {
           struct kref refs;
           struct list_head regions;
   };
   
   static struct resv_map *resv_map_alloc(void)
   {
           struct resv_map *resv_map = kmalloc(sizeof(*resv_map), GFP_KERNEL);
           if (!resv_map)
                   return NULL;
   
           kref_init(&resv_map->refs);
           INIT_LIST_HEAD(&resv_map->regions);
   
           return resv_map;
   }
   
   static void resv_map_release(struct kref *ref)
   {
           struct resv_map *resv_map = container_of(ref, struct resv_map, refs);
   
           /* Clear out any active regions before we release the map. */
           region_truncate(&resv_map->regions, 0);
           kfree(resv_map);
   }
   
   static struct resv_map *vma_resv_map(struct vm_area_struct *vma)
   {
           VM_BUG_ON(!is_vm_hugetlb_page(vma));
           if (!(vma->vm_flags & VM_MAYSHARE))
                   return (struct resv_map *)(get_vma_private_data(vma) &
                                                           ~HPAGE_RESV_MASK);
           return NULL;
   }
   
   static void set_vma_resv_map(struct vm_area_struct *vma, struct resv_map *map)
   {
           VM_BUG_ON(!is_vm_hugetlb_page(vma));
           VM_BUG_ON(vma->vm_flags & VM_MAYSHARE);
   
           set_vma_private_data(vma, (get_vma_private_data(vma) &
                                   HPAGE_RESV_MASK) | (unsigned long)map);
   }
   
   static void set_vma_resv_flags(struct vm_area_struct *vma, unsigned long flags)
   {
           VM_BUG_ON(!is_vm_hugetlb_page(vma));
           VM_BUG_ON(vma->vm_flags & VM_MAYSHARE);
   
           set_vma_private_data(vma, get_vma_private_data(vma) | flags);
   }
   
   static int is_vma_resv_set(struct vm_area_struct *vma, unsigned long flag)
   {
           VM_BUG_ON(!is_vm_hugetlb_page(vma));
   
           return (get_vma_private_data(vma) & flag) != 0;
   }
   
   /* Decrement the reserved pages in the hugepage pool by one */
   static void decrement_hugepage_resv_vma(struct hstate *h,
                           struct vm_area_struct *vma)
   {
           if (vma->vm_flags & VM_NORESERVE)
                   return;
   
           if (vma->vm_flags & VM_MAYSHARE) {
                   /* Shared mappings always use reserves */
                   h->resv_huge_pages--;
           } else if (is_vma_resv_set(vma, HPAGE_RESV_OWNER)) {
                   /*
                    * Only the process that called mmap() has reserves for
                    * private mappings.
                    */
                   h->resv_huge_pages--;
           }
   }
   
   /* Reset counters to 0 and clear all HPAGE_RESV_* flags */
   void reset_vma_resv_huge_pages(struct vm_area_struct *vma)
   {
           VM_BUG_ON(!is_vm_hugetlb_page(vma));
           if (!(vma->vm_flags & VM_MAYSHARE))
                   vma->vm_private_data = (void *)0;
   }
   
   /* Returns true if the VMA has associated reserve pages */
   static int vma_has_reserves(struct vm_area_struct *vma)
   {
           if (vma->vm_flags & VM_MAYSHARE)
                   return 1;
           if (is_vma_resv_set(vma, HPAGE_RESV_OWNER))
                   return 1;
           return 0;
   }
   
   static void copy_gigantic_page(struct page *dst, struct page *src)
   {
           int i;
           struct hstate *h = page_hstate(src);
           struct page *dst_base = dst;
           struct page *src_base = src;
   
           for (i = 0; i < pages_per_huge_page(h); ) {
                   cond_resched();
                   copy_highpage(dst, src);
   
                   i++;
                   dst = mem_map_next(dst, dst_base, i);
                   src = mem_map_next(src, src_base, i);
           }
   }
   
   void copy_huge_page(struct page *dst, struct page *src)
   {
           int i;
           struct hstate *h = page_hstate(src);
   
           if (unlikely(pages_per_huge_page(h) > MAX_ORDER_NR_PAGES)) {
                   copy_gigantic_page(dst, src);
                   return;
           }
   
           might_sleep();
           for (i = 0; i < pages_per_huge_page(h); i++) {
                   cond_resched();
                   copy_highpage(dst + i, src + i);
           }
   }
   
   static void enqueue_huge_page(struct hstate *h, struct page *page)
   {
           int nid = page_to_nid(page);
           list_move(&page->lru, &h->hugepage_freelists[nid]);
           h->free_huge_pages++;
           h->free_huge_pages_node[nid]++;
   }
   
   static struct page *dequeue_huge_page_node(struct hstate *h, int nid)
   {
           struct page *page;
   
           if (list_empty(&h->hugepage_freelists[nid]))
                   return NULL;
           page = list_entry(h->hugepage_freelists[nid].next, struct page, lru);
           list_move(&page->lru, &h->hugepage_activelist);
           set_page_refcounted(page);
           h->free_huge_pages--;
           h->free_huge_pages_node[nid]--;
           return page;
   }
   
   static struct page *dequeue_huge_page_vma(struct hstate *h,
                                   struct vm_area_struct *vma,
                                   unsigned long address, int avoid_reserve)
   {
           struct page *page = NULL;
           struct mempolicy *mpol;
           nodemask_t *nodemask;
           struct zonelist *zonelist;
           struct zone *zone;
           struct zoneref *z;
           unsigned int cpuset_mems_cookie;
   
   retry_cpuset:
           cpuset_mems_cookie = get_mems_allowed();
           zonelist = huge_zonelist(vma, address,
                                           htlb_alloc_mask, &mpol, &nodemask);
           /*
            * A child process with MAP_PRIVATE mappings created by their parent
            * have no page reserves. This check ensures that reservations are
            * not "stolen". The child may still get SIGKILLed
            */
           if (!vma_has_reserves(vma) &&
                           h->free_huge_pages - h->resv_huge_pages == 0)
                   goto err;
   
           /* If reserves cannot be used, ensure enough pages are in the pool */
           if (avoid_reserve && h->free_huge_pages - h->resv_huge_pages == 0)
                   goto err;
   
           for_each_zone_zonelist_nodemask(zone, z, zonelist,
                                                   MAX_NR_ZONES - 1, nodemask) {
                   if (cpuset_zone_allowed_softwall(zone, htlb_alloc_mask)) {
                           page = dequeue_huge_page_node(h, zone_to_nid(zone));
                           if (page) {
                                   if (!avoid_reserve)
                                           decrement_hugepage_resv_vma(h, vma);
                                   break;
                           }
                   }
           }
   
           mpol_cond_put(mpol);
           if (unlikely(!put_mems_allowed(cpuset_mems_cookie) && !page))
                   goto retry_cpuset;
           return page;
   
   err:
           mpol_cond_put(mpol);
           return NULL;
   }
   
   static void update_and_free_page(struct hstate *h, struct page *page)
   {
           int i;
   
           VM_BUG_ON(h->order >= MAX_ORDER);
   
           h->nr_huge_pages--;
           h->nr_huge_pages_node[page_to_nid(page)]--;
           for (i = 0; i < pages_per_huge_page(h); i++) {
                   page[i].flags &= ~(1 << PG_locked | 1 << PG_error |
                                   1 << PG_referenced | 1 << PG_dirty |
                                   1 << PG_active | 1 << PG_reserved |
                                   1 << PG_private | 1 << PG_writeback);
           }
           VM_BUG_ON(hugetlb_cgroup_from_page(page));
           set_compound_page_dtor(page, NULL);
           set_page_refcounted(page);
           arch_release_hugepage(page);
           __free_pages(page, huge_page_order(h));
   }
   
   struct hstate *size_to_hstate(unsigned long size)
   {
           struct hstate *h;
   
           for_each_hstate(h) {
                   if (huge_page_size(h) == size)
                           return h;
           }
           return NULL;
   }
   
   static void free_huge_page(struct page *page)
   {
           /*
            * Can't pass hstate in here because it is called from the
            * compound page destructor.
            */
           struct hstate *h = page_hstate(page);
           int nid = page_to_nid(page);
           struct hugepage_subpool *spool =
                   (struct hugepage_subpool *)page_private(page);
   
           set_page_private(page, 0);
           page->mapping = NULL;
           BUG_ON(page_count(page));
           BUG_ON(page_mapcount(page));
   
           spin_lock(&hugetlb_lock);
           hugetlb_cgroup_uncharge_page(hstate_index(h),
                                        pages_per_huge_page(h), page);
           if (h->surplus_huge_pages_node[nid] && huge_page_order(h) < MAX_ORDER) {
                   /* remove the page from active list */
                   list_del(&page->lru);
                   update_and_free_page(h, page);
                   h->surplus_huge_pages--;
                   h->surplus_huge_pages_node[nid]--;
           } else {
                   arch_clear_hugepage_flags(page);
                   enqueue_huge_page(h, page);
           }
           spin_unlock(&hugetlb_lock);
           hugepage_subpool_put_pages(spool, 1);
   }
   
   static void prep_new_huge_page(struct hstate *h, struct page *page, int nid)
   {
           INIT_LIST_HEAD(&page->lru);
           set_compound_page_dtor(page, free_huge_page);
           spin_lock(&hugetlb_lock);
           set_hugetlb_cgroup(page, NULL);
           h->nr_huge_pages++;
           h->nr_huge_pages_node[nid]++;
           spin_unlock(&hugetlb_lock);
           put_page(page); /* free it into the hugepage allocator */
   }
   
   static void prep_compound_gigantic_page(struct page *page, unsigned long order)
   {
           int i;
           int nr_pages = 1 << order;
           struct page *p = page + 1;
   
           /* we rely on prep_new_huge_page to set the destructor */
           set_compound_order(page, order);
           __SetPageHead(page);
           for (i = 1; i < nr_pages; i++, p = mem_map_next(p, page, i)) {
                   __SetPageTail(p);
                   set_page_count(p, 0);
                   p->first_page = page;
           }
   }
   
   /*
    * PageHuge() only returns true for hugetlbfs pages, but not for normal or
    * transparent huge pages.  See the PageTransHuge() documentation for more
    * details.
    */
   int PageHuge(struct page *page)
   {
           compound_page_dtor *dtor;
   
           if (!PageCompound(page))
                   return 0;
   
           page = compound_head(page);
           dtor = get_compound_page_dtor(page);
   
           return dtor == free_huge_page;
   }
   EXPORT_SYMBOL_GPL(PageHuge);
   
   static struct page *alloc_fresh_huge_page_node(struct hstate *h, int nid)
   {
           struct page *page;
   
           if (h->order >= MAX_ORDER)
                   return NULL;
   
           page = alloc_pages_exact_node(nid,
                   htlb_alloc_mask|__GFP_COMP|__GFP_THISNODE|
                                                   __GFP_REPEAT|__GFP_NOWARN,
                   huge_page_order(h));
           if (page) {
                   if (arch_prepare_hugepage(page)) {
                           __free_pages(page, huge_page_order(h));
                           return NULL;
                   }
                   prep_new_huge_page(h, page, nid);
           }
   
           return page;
   }
   
   /*
    * common helper functions for hstate_next_node_to_{alloc|free}.
    * We may have allocated or freed a huge page based on a different
    * nodes_allowed previously, so h->next_node_to_{alloc|free} might
    * be outside of *nodes_allowed.  Ensure that we use an allowed
    * node for alloc or free.
    */
   static int next_node_allowed(int nid, nodemask_t *nodes_allowed)
   {
           nid = next_node(nid, *nodes_allowed);
           if (nid == MAX_NUMNODES)
                   nid = first_node(*nodes_allowed);
           VM_BUG_ON(nid >= MAX_NUMNODES);
   
           return nid;
   }
   
   static int get_valid_node_allowed(int nid, nodemask_t *nodes_allowed)
   {
           if (!node_isset(nid, *nodes_allowed))
                   nid = next_node_allowed(nid, nodes_allowed);
           return nid;
   }
   
   /*
    * returns the previously saved node ["this node"] from which to
    * allocate a persistent huge page for the pool and advance the
    * next node from which to allocate, handling wrap at end of node
    * mask.
    */
   static int hstate_next_node_to_alloc(struct hstate *h,
                                           nodemask_t *nodes_allowed)
   {
           int nid;
   
           VM_BUG_ON(!nodes_allowed);
   
           nid = get_valid_node_allowed(h->next_nid_to_alloc, nodes_allowed);
           h->next_nid_to_alloc = next_node_allowed(nid, nodes_allowed);
   
           return nid;
   }
   
   static int alloc_fresh_huge_page(struct hstate *h, nodemask_t *nodes_allowed)
   {
           struct page *page;
           int start_nid;
           int next_nid;
           int ret = 0;
   
           start_nid = hstate_next_node_to_alloc(h, nodes_allowed);
           next_nid = start_nid;
   
           do {
                   page = alloc_fresh_huge_page_node(h, next_nid);
                   if (page) {
                           ret = 1;
                           break;
                   }
                   next_nid = hstate_next_node_to_alloc(h, nodes_allowed);
           } while (next_nid != start_nid);
   
           if (ret)
                   count_vm_event(HTLB_BUDDY_PGALLOC);
           else
                   count_vm_event(HTLB_BUDDY_PGALLOC_FAIL);
   
           return ret;
   }
   
   /*
    * helper for free_pool_huge_page() - return the previously saved
    * node ["this node"] from which to free a huge page.  Advance the
    * next node id whether or not we find a free huge page to free so
    * that the next attempt to free addresses the next node.
    */
   static int hstate_next_node_to_free(struct hstate *h, nodemask_t *nodes_allowed)
   {
           int nid;
   
           VM_BUG_ON(!nodes_allowed);
   
           nid = get_valid_node_allowed(h->next_nid_to_free, nodes_allowed);
           h->next_nid_to_free = next_node_allowed(nid, nodes_allowed);
   
           return nid;
   }
   
   /*
    * Free huge page from pool from next node to free.
    * Attempt to keep persistent huge pages more or less
    * balanced over allowed nodes.
    * Called with hugetlb_lock locked.
    */
   static int free_pool_huge_page(struct hstate *h, nodemask_t *nodes_allowed,
                                                            bool acct_surplus)
   {
           int start_nid;
           int next_nid;
           int ret = 0;
   
           start_nid = hstate_next_node_to_free(h, nodes_allowed);
           next_nid = start_nid;
   
           do {
                   /*
                    * If we're returning unused surplus pages, only examine
                    * nodes with surplus pages.
                    */
                   if ((!acct_surplus || h->surplus_huge_pages_node[next_nid]) &&
                       !list_empty(&h->hugepage_freelists[next_nid])) {
                           struct page *page =
                                   list_entry(h->hugepage_freelists[next_nid].next,
                                             struct page, lru);
                           list_del(&page->lru);
                           h->free_huge_pages--;
                           h->free_huge_pages_node[next_nid]--;
                           if (acct_surplus) {
                                   h->surplus_huge_pages--;
                                   h->surplus_huge_pages_node[next_nid]--;
                           }
                           update_and_free_page(h, page);
                           ret = 1;
                           break;
                   }
                   next_nid = hstate_next_node_to_free(h, nodes_allowed);
           } while (next_nid != start_nid);
   
           return ret;
   }
   
   static struct page *alloc_buddy_huge_page(struct hstate *h, int nid)
   {
           struct page *page;
           unsigned int r_nid;
   
           if (h->order >= MAX_ORDER)
                   return NULL;
   
           /*
            * Assume we will successfully allocate the surplus page to
            * prevent racing processes from causing the surplus to exceed
            * overcommit
            *
            * This however introduces a different race, where a process B
            * tries to grow the static hugepage pool while alloc_pages() is
            * called by process A. B will only examine the per-node
            * counters in determining if surplus huge pages can be
            * converted to normal huge pages in adjust_pool_surplus(). A
            * won't be able to increment the per-node counter, until the
            * lock is dropped by B, but B doesn't drop hugetlb_lock until
            * no more huge pages can be converted from surplus to normal
            * state (and doesn't try to convert again). Thus, we have a
            * case where a surplus huge page exists, the pool is grown, and
            * the surplus huge page still exists after, even though it
            * should just have been converted to a normal huge page. This
            * does not leak memory, though, as the hugepage will be freed
            * once it is out of use. It also does not allow the counters to
            * go out of whack in adjust_pool_surplus() as we don't modify
            * the node values until we've gotten the hugepage and only the
            * per-node value is checked there.
            */
           spin_lock(&hugetlb_lock);
           if (h->surplus_huge_pages >= h->nr_overcommit_huge_pages) {
                   spin_unlock(&hugetlb_lock);
                   return NULL;
           } else {
                   h->nr_huge_pages++;
                   h->surplus_huge_pages++;
           }
           spin_unlock(&hugetlb_lock);
   
           if (nid == NUMA_NO_NODE)
                   page = alloc_pages(htlb_alloc_mask|__GFP_COMP|
                                      __GFP_REPEAT|__GFP_NOWARN,
                                      huge_page_order(h));
           else
                   page = alloc_pages_exact_node(nid,
                           htlb_alloc_mask|__GFP_COMP|__GFP_THISNODE|
                           __GFP_REPEAT|__GFP_NOWARN, huge_page_order(h));
   
           if (page && arch_prepare_hugepage(page)) {
                   __free_pages(page, huge_page_order(h));
                   page = NULL;
           }
   
           spin_lock(&hugetlb_lock);
           if (page) {
                   INIT_LIST_HEAD(&page->lru);
                   r_nid = page_to_nid(page);
                   set_compound_page_dtor(page, free_huge_page);
                   set_hugetlb_cgroup(page, NULL);
                   /*
                    * We incremented the global counters already
                    */
                   h->nr_huge_pages_node[r_nid]++;
                   h->surplus_huge_pages_node[r_nid]++;
                   __count_vm_event(HTLB_BUDDY_PGALLOC);
           } else {
                   h->nr_huge_pages--;
                   h->surplus_huge_pages--;
                   __count_vm_event(HTLB_BUDDY_PGALLOC_FAIL);
           }
           spin_unlock(&hugetlb_lock);
   
           return page;
   }
   
   /*
    * This allocation function is useful in the context where vma is irrelevant.
    * E.g. soft-offlining uses this function because it only cares physical
    * address of error page.
    */
   struct page *alloc_huge_page_node(struct hstate *h, int nid)
   {
           struct page *page;
   
           spin_lock(&hugetlb_lock);
           page = dequeue_huge_page_node(h, nid);
           spin_unlock(&hugetlb_lock);
   
           if (!page)
                   page = alloc_buddy_huge_page(h, nid);
   
           return page;
   }
   
   /*
    * Increase the hugetlb pool such that it can accommodate a reservation
    * of size 'delta'.
    */
   static int gather_surplus_pages(struct hstate *h, int delta)
   {
           struct list_head surplus_list;
           struct page *page, *tmp;
           int ret, i;
           int needed, allocated;
           bool alloc_ok = true;
   
           needed = (h->resv_huge_pages + delta) - h->free_huge_pages;
           if (needed <= 0) {
                   h->resv_huge_pages += delta;
                   return 0;
           }
   
           allocated = 0;
           INIT_LIST_HEAD(&surplus_list);
   
           ret = -ENOMEM;
   retry:
           spin_unlock(&hugetlb_lock);
           for (i = 0; i < needed; i++) {
                   page = alloc_buddy_huge_page(h, NUMA_NO_NODE);
                   if (!page) {
                           alloc_ok = false;
                           break;
                   }
                   list_add(&page->lru, &surplus_list);
           }
           allocated += i;
   
           /*
            * After retaking hugetlb_lock, we need to recalculate 'needed'
            * because either resv_huge_pages or free_huge_pages may have changed.
            */
           spin_lock(&hugetlb_lock);
           needed = (h->resv_huge_pages + delta) -
                           (h->free_huge_pages + allocated);
           if (needed > 0) {
                   if (alloc_ok)
                           goto retry;
                   /*
                    * We were not able to allocate enough pages to
                    * satisfy the entire reservation so we free what
                    * we've allocated so far.
                    */
                   goto free;
           }
           /*
            * The surplus_list now contains _at_least_ the number of extra pages
            * needed to accommodate the reservation.  Add the appropriate number
            * of pages to the hugetlb pool and free the extras back to the buddy
            * allocator.  Commit the entire reservation here to prevent another
            * process from stealing the pages as they are added to the pool but
            * before they are reserved.
           */
          needed += allocated;
          h->resv_huge_pages += delta;
          ret = 0;
  
          /* Free the needed pages to the hugetlb pool */
          list_for_each_entry_safe(page, tmp, &surplus_list, lru) {
                  if ((--needed) < 0)
                          break;
                  /*
                   * This page is now managed by the hugetlb allocator and has
                   * no users -- drop the buddy allocator's reference.
                   */
                  put_page_testzero(page);
                  VM_BUG_ON(page_count(page));
                  enqueue_huge_page(h, page);
          }
  free:
          spin_unlock(&hugetlb_lock);
  
          /* Free unnecessary surplus pages to the buddy allocator */
          if (!list_empty(&surplus_list)) {
                  list_for_each_entry_safe(page, tmp, &surplus_list, lru) {
                          put_page(page);
                  }
          }
          spin_lock(&hugetlb_lock);
  
          return ret;
  }
  
  /*
   * When releasing a hugetlb pool reservation, any surplus pages that were
   * allocated to satisfy the reservation must be explicitly freed if they were
   * never used.
   * Called with hugetlb_lock held.
   */
  static void return_unused_surplus_pages(struct hstate *h,
                                          unsigned long unused_resv_pages)
  {
          unsigned long nr_pages;
  
          /* Uncommit the reservation */
          h->resv_huge_pages -= unused_resv_pages;
  
          /* Cannot return gigantic pages currently */
          if (h->order >= MAX_ORDER)
                  return;
  
          nr_pages = min(unused_resv_pages, h->surplus_huge_pages);
  
          /*
           * We want to release as many surplus pages as possible, spread
           * evenly across all nodes with memory. Iterate across these nodes
           * until we can no longer free unreserved surplus pages. This occurs
           * when the nodes with surplus pages have no free pages.
           * free_pool_huge_page() will balance the the freed pages across the
           * on-line nodes with memory and will handle the hstate accounting.
           */
          while (nr_pages--) {
                  if (!free_pool_huge_page(h, &node_states[N_MEMORY], 1))
                          break;
          }
  }
  
  /*
   * Determine if the huge page at addr within the vma has an associated
   * reservation.  Where it does not we will need to logically increase
   * reservation and actually increase subpool usage before an allocation
   * can occur.  Where any new reservation would be required the
   * reservation change is prepared, but not committed.  Once the page
   * has been allocated from the subpool and instantiated the change should
   * be committed via vma_commit_reservation.  No action is required on
   * failure.
   */
  static long vma_needs_reservation(struct hstate *h,
                          struct vm_area_struct *vma, unsigned long addr)
  {
          struct address_space *mapping = vma->vm_file->f_mapping;
          struct inode *inode = mapping->host;
  
          if (vma->vm_flags & VM_MAYSHARE) {
                  pgoff_t idx = vma_hugecache_offset(h, vma, addr);
                  return region_chg(&inode->i_mapping->private_list,
                                                          idx, idx + 1);
  
          } else if (!is_vma_resv_set(vma, HPAGE_RESV_OWNER)) {
                  return 1;
  
          } else  {
                  long err;
                  pgoff_t idx = vma_hugecache_offset(h, vma, addr);
                  struct resv_map *reservations = vma_resv_map(vma);
  
                  err = region_chg(&reservations->regions, idx, idx + 1);
                  if (err < 0)
                          return err;
                  return 0;
          }
  }
  static void vma_commit_reservation(struct hstate *h,
                          struct vm_area_struct *vma, unsigned long addr)
  {
          struct address_space *mapping = vma->vm_file->f_mapping;
          struct inode *inode = mapping->host;
  
          if (vma->vm_flags & VM_MAYSHARE) {
                  pgoff_t idx = vma_hugecache_offset(h, vma, addr);
                  region_add(&inode->i_mapping->private_list, idx, idx + 1);
  
          } else if (is_vma_resv_set(vma, HPAGE_RESV_OWNER)) {
                  pgoff_t idx = vma_hugecache_offset(h, vma, addr);
                  struct resv_map *reservations = vma_resv_map(vma);
  
                  /* Mark this page used in the map. */
                  region_add(&reservations->regions, idx, idx + 1);
          }
  }
  
  static struct page *alloc_huge_page(struct vm_area_struct *vma,
                                      unsigned long addr, int avoid_reserve)
  {
          struct hugepage_subpool *spool = subpool_vma(vma);
          struct hstate *h = hstate_vma(vma);
          struct page *page;
          long chg;
          int ret, idx;
          struct hugetlb_cgroup *h_cg;
  
          idx = hstate_index(h);
          /*
           * Processes that did not create the mapping will have no
           * reserves and will not have accounted against subpool
           * limit. Check that the subpool limit can be made before
           * satisfying the allocation MAP_NORESERVE mappings may also
           * need pages and subpool limit allocated allocated if no reserve
           * mapping overlaps.
           */
          chg = vma_needs_reservation(h, vma, addr);
          if (chg < 0)
                  return ERR_PTR(-ENOMEM);
          if (chg)
                  if (hugepage_subpool_get_pages(spool, chg))
                          return ERR_PTR(-ENOSPC);
  
          ret = hugetlb_cgroup_charge_cgroup(idx, pages_per_huge_page(h), &h_cg);
          if (ret) {
                  hugepage_subpool_put_pages(spool, chg);
                  return ERR_PTR(-ENOSPC);
          }
          spin_lock(&hugetlb_lock);
          page = dequeue_huge_page_vma(h, vma, addr, avoid_reserve);
          if (page) {
                  /* update page cgroup details */
                  hugetlb_cgroup_commit_charge(idx, pages_per_huge_page(h),
                                               h_cg, page);
                  spin_unlock(&hugetlb_lock);
          } else {
                  spin_unlock(&hugetlb_lock);
                  page = alloc_buddy_huge_page(h, NUMA_NO_NODE);
                  if (!page) {
                          hugetlb_cgroup_uncharge_cgroup(idx,
                                                         pages_per_huge_page(h),
                                                         h_cg);
                          hugepage_subpool_put_pages(spool, chg);
                          return ERR_PTR(-ENOSPC);
                  }
                  spin_lock(&hugetlb_lock);
                  hugetlb_cgroup_commit_charge(idx, pages_per_huge_page(h),
                                               h_cg, page);
                  list_move(&page->lru, &h->hugepage_activelist);
                  spin_unlock(&hugetlb_lock);
          }
  
          set_page_private(page, (unsigned long)spool);
  
          vma_commit_reservation(h, vma, addr);
          return page;
  }
  
  int __weak alloc_bootmem_huge_page(struct hstate *h)
  {
          struct huge_bootmem_page *m;
          int nr_nodes = nodes_weight(node_states[N_MEMORY]);
  
          while (nr_nodes) {
                  void *addr;
  
                  addr = __alloc_bootmem_node_nopanic(
                                  NODE_DATA(hstate_next_node_to_alloc(h,
                                                  &node_states[N_MEMORY])),
                                  huge_page_size(h), huge_page_size(h), 0);
  
                  if (addr) {
                          /*
                           * Use the beginning of the huge page to store the
                           * huge_bootmem_page struct (until gather_bootmem
                           * puts them into the mem_map).
                           */
                          m = addr;
                          goto found;
                  }
                  nr_nodes--;
          }
          return 0;
  
  found:
          BUG_ON((unsigned long)virt_to_phys(m) & (huge_page_size(h) - 1));
          /* Put them into a private list first because mem_map is not up yet */
          list_add(&m->list, &huge_boot_pages);
          m->hstate = h;
          return 1;
  }
  
  static void prep_compound_huge_page(struct page *page, int order)
  {
          if (unlikely(order > (MAX_ORDER - 1)))
                  prep_compound_gigantic_page(page, order);
          else
                  prep_compound_page(page, order);
  }
  
  /* Put bootmem huge pages into the standard lists after mem_map is up */
  static void __init gather_bootmem_prealloc(void)
  {
          struct huge_bootmem_page *m;
  
          list_for_each_entry(m, &huge_boot_pages, list) {
                  struct hstate *h = m->hstate;
                  struct page *page;
  
  #ifdef CONFIG_HIGHMEM
                  page = pfn_to_page(m->phys >> PAGE_SHIFT);
                  free_bootmem_late((unsigned long)m,
                                    sizeof(struct huge_bootmem_page));
  #else
                  page = virt_to_page(m);
  #endif
                  __ClearPageReserved(page);
                  WARN_ON(page_count(page) != 1);
                  prep_compound_huge_page(page, h->order);
                  prep_new_huge_page(h, page, page_to_nid(page));
                  /*
                   * If we had gigantic hugepages allocated at boot time, we need
                   * to restore the 'stolen' pages to totalram_pages in order to
                   * fix confusing memory reports from free(1) and another
                   * side-effects, like CommitLimit going negative.
                   */
                  if (h->order > (MAX_ORDER - 1))
                          totalram_pages += 1 << h->order;
          }
  }
  
  static void __init hugetlb_hstate_alloc_pages(struct hstate *h)
  {
          unsigned long i;
  
          for (i = 0; i < h->max_huge_pages; ++i) {
                  if (h->order >= MAX_ORDER) {
                          if (!alloc_bootmem_huge_page(h))
                                  break;
                  } else if (!alloc_fresh_huge_page(h,
                                           &node_states[N_MEMORY]))
                          break;
          }
          h->max_huge_pages = i;
  }
  
  static void __init hugetlb_init_hstates(void)
  {
          struct hstate *h;
  
          for_each_hstate(h) {
                  /* oversize hugepages were init'ed in early boot */
                  if (h->order < MAX_ORDER)
                          hugetlb_hstate_alloc_pages(h);
          }
  }
  
  static char * __init memfmt(char *buf, unsigned long n)
  {
          if (n >= (1UL << 30))
                  sprintf(buf, "%lu GB", n >> 30);
          else if (n >= (1UL << 20))
                  sprintf(buf, "%lu MB", n >> 20);
          else
                  sprintf(buf, "%lu KB", n >> 10);
          return buf;
  }
  
  static void __init report_hugepages(void)
  {
          struct hstate *h;
  
          for_each_hstate(h) {
                  char buf[32];
                  printk(KERN_INFO "HugeTLB registered %s page size, "
                                   "pre-allocated %ld pages\n",
                          memfmt(buf, huge_page_size(h)),
                          h->free_huge_pages);
          }
  }
  
  #ifdef CONFIG_HIGHMEM
  static void try_to_free_low(struct hstate *h, unsigned long count,
                                                  nodemask_t *nodes_allowed)
  {
          int i;
  
          if (h->order >= MAX_ORDER)
                  return;
  
          for_each_node_mask(i, *nodes_allowed) {
                  struct page *page, *next;
                  struct list_head *freel = &h->hugepage_freelists[i];
                  list_for_each_entry_safe(page, next, freel, lru) {
                          if (count >= h->nr_huge_pages)
                                  return;
                          if (PageHighMem(page))
                                  continue;
                          list_del(&page->lru);
                          update_and_free_page(h, page);
                          h->free_huge_pages--;
                          h->free_huge_pages_node[page_to_nid(page)]--;
                  }
          }
  }
  #else
  static inline void try_to_free_low(struct hstate *h, unsigned long count,
                                                  nodemask_t *nodes_allowed)
  {
  }
  #endif
  
  /*
   * Increment or decrement surplus_huge_pages.  Keep node-specific counters
   * balanced by operating on them in a round-robin fashion.
   * Returns 1 if an adjustment was made.
   */
  static int adjust_pool_surplus(struct hstate *h, nodemask_t *nodes_allowed,
                                  int delta)
  {
          int start_nid, next_nid;
          int ret = 0;
  
          VM_BUG_ON(delta != -1 && delta != 1);
  
          if (delta < 0)
                  start_nid = hstate_next_node_to_alloc(h, nodes_allowed);
          else
                  start_nid = hstate_next_node_to_free(h, nodes_allowed);
          next_nid = start_nid;
  
          do {
                  int nid = next_nid;
                  if (delta < 0)  {
                          /*
                           * To shrink on this node, there must be a surplus page
                           */
                          if (!h->surplus_huge_pages_node[nid]) {
                                  next_nid = hstate_next_node_to_alloc(h,
                                                                  nodes_allowed);
                                  continue;
                          }
                  }
                  if (delta > 0) {
                          /*
                           * Surplus cannot exceed the total number of pages
                           */
                          if (h->surplus_huge_pages_node[nid] >=
                                                  h->nr_huge_pages_node[nid]) {
                                  next_nid = hstate_next_node_to_free(h,
                                                                  nodes_allowed);
                                  continue;
                          }
                  }
  
                  h->surplus_huge_pages += delta;
                  h->surplus_huge_pages_node[nid] += delta;
                  ret = 1;
                  break;
          } while (next_nid != start_nid);
  
          return ret;
  }
  
  #define persistent_huge_pages(h) (h->nr_huge_pages - h->surplus_huge_pages)
  static unsigned long set_max_huge_pages(struct hstate *h, unsigned long count,
                                                  nodemask_t *nodes_allowed)
  {
          unsigned long min_count, ret;
  
          if (h->order >= MAX_ORDER)
                  return h->max_huge_pages;
  
          /*
           * Increase the pool size
           * First take pages out of surplus state.  Then make up the
           * remaining difference by allocating fresh huge pages.
           *
           * We might race with alloc_buddy_huge_page() here and be unable
           * to convert a surplus huge page to a normal huge page. That is
           * not critical, though, it just means the overall size of the
           * pool might be one hugepage larger than it needs to be, but
           * within all the constraints specified by the sysctls.
           */
          spin_lock(&hugetlb_lock);
          while (h->surplus_huge_pages && count > persistent_huge_pages(h)) {
                  if (!adjust_pool_surplus(h, nodes_allowed, -1))
                          break;
          }
  
          while (count > persistent_huge_pages(h)) {
                  /*
                   * If this allocation races such that we no longer need the
                   * page, free_huge_page will handle it by freeing the page
                   * and reducing the surplus.
                   */
                  spin_unlock(&hugetlb_lock);
                  ret = alloc_fresh_huge_page(h, nodes_allowed);
                  spin_lock(&hugetlb_lock);
                  if (!ret)
                          goto out;
  
                  /* Bail for signals. Probably ctrl-c from user */
                  if (signal_pending(current))
                          goto out;
          }
  
          /*
           * Decrease the pool size
           * First return free pages to the buddy allocator (being careful
           * to keep enough around to satisfy reservations).  Then place
           * pages into surplus state as needed so the pool will shrink
           * to the desired size as pages become free.
           *
           * By placing pages into the surplus state independent of the
           * overcommit value, we are allowing the surplus pool size to
           * exceed overcommit. There are few sane options here. Since
           * alloc_buddy_huge_page() is checking the global counter,
           * though, we'll note that we're not allowed to exceed surplus
           * and won't grow the pool anywhere else. Not until one of the
           * sysctls are changed, or the surplus pages go out of use.
           */
          min_count = h->resv_huge_pages + h->nr_huge_pages - h->free_huge_pages;
          min_count = max(count, min_count);
          try_to_free_low(h, min_count, nodes_allowed);
          while (min_count < persistent_huge_pages(h)) {
                  if (!free_pool_huge_page(h, nodes_allowed, 0))
                          break;
          }
          while (count < persistent_huge_pages(h)) {
                  if (!adjust_pool_surplus(h, nodes_allowed, 1))
                          break;
          }
  out:
          ret = persistent_huge_pages(h);
          spin_unlock(&hugetlb_lock);
          return ret;
  }
  
  #define HSTATE_ATTR_RO(_name) \
          static struct kobj_attribute _name##_attr = __ATTR_RO(_name)
  
  #define HSTATE_ATTR(_name) \
          static struct kobj_attribute _name##_attr = \
                  __ATTR(_name, 0644, _name##_show, _name##_store)
  
  static struct kobject *hugepages_kobj;
  static struct kobject *hstate_kobjs[HUGE_MAX_HSTATE];
  
  static struct hstate *kobj_to_node_hstate(struct kobject *kobj, int *nidp);
  
  static struct hstate *kobj_to_hstate(struct kobject *kobj, int *nidp)
  {
          int i;
  
          for (i = 0; i < HUGE_MAX_HSTATE; i++)
                  if (hstate_kobjs[i] == kobj) {
                          if (nidp)
                                  *nidp = NUMA_NO_NODE;
                          return &hstates[i];
                  }
  
          return kobj_to_node_hstate(kobj, nidp);
  }
  
  static ssize_t nr_hugepages_show_common(struct kobject *kobj,
                                          struct kobj_attribute *attr, char *buf)
  {
          struct hstate *h;
          unsigned long nr_huge_pages;
          int nid;
  
          h = kobj_to_hstate(kobj, &nid);
          if (nid == NUMA_NO_NODE)
                  nr_huge_pages = h->nr_huge_pages;
          else
                  nr_huge_pages = h->nr_huge_pages_node[nid];
  
          return sprintf(buf, "%lu\n", nr_huge_pages);
  }
  
  static ssize_t nr_hugepages_store_common(bool obey_mempolicy,
                          struct kobject *kobj, struct kobj_attribute *attr,
                          const char *buf, size_t len)
  {
          int err;
          int nid;
          unsigned long count;
          struct hstate *h;
          NODEMASK_ALLOC(nodemask_t, nodes_allowed, GFP_KERNEL | __GFP_NORETRY);
  
          err = strict_strtoul(buf, 10, &count);
          if (err)
                  goto out;
  
          h = kobj_to_hstate(kobj, &nid);
          if (h->order >= MAX_ORDER) {
                  err = -EINVAL;
                  goto out;
          }
  
          if (nid == NUMA_NO_NODE) {
                  /*
                   * global hstate attribute
                   */
                  if (!(obey_mempolicy &&
                                  init_nodemask_of_mempolicy(nodes_allowed))) {
                          NODEMASK_FREE(nodes_allowed);
                          nodes_allowed = &node_states[N_MEMORY];
                  }
          } else if (nodes_allowed) {
                  /*
                   * per node hstate attribute: adjust count to global,
                   * but restrict alloc/free to the specified node.
                   */
                  count += h->nr_huge_pages - h->nr_huge_pages_node[nid];
                  init_nodemask_of_node(nodes_allowed, nid);
          } else
                  nodes_allowed = &node_states[N_MEMORY];
  
          h->max_huge_pages = set_max_huge_pages(h, count, nodes_allowed);
  
          if (nodes_allowed != &node_states[N_MEMORY])
                  NODEMASK_FREE(nodes_allowed);
  
          return len;
  out:
          NODEMASK_FREE(nodes_allowed);
          return err;
  }
  
  static ssize_t nr_hugepages_show(struct kobject *kobj,
                                         struct kobj_attribute *attr, char *buf)
  {
          return nr_hugepages_show_common(kobj, attr, buf);
  }
  
  static ssize_t nr_hugepages_store(struct kobject *kobj,
                 struct kobj_attribute *attr, const char *buf, size_t len)
  {
          return nr_hugepages_store_common(false, kobj, attr, buf, len);
  }
  HSTATE_ATTR(nr_hugepages);
  
  #ifdef CONFIG_NUMA
  
  /*
   * hstate attribute for optionally mempolicy-based constraint on persistent
   * huge page alloc/free.
   */
  static ssize_t nr_hugepages_mempolicy_show(struct kobject *kobj,
                                         struct kobj_attribute *attr, char *buf)
  {
          return nr_hugepages_show_common(kobj, attr, buf);
  }
  
  static ssize_t nr_hugepages_mempolicy_store(struct kobject *kobj,
                 struct kobj_attribute *attr, const char *buf, size_t len)
  {
          return nr_hugepages_store_common(true, kobj, attr, buf, len);
  }
  HSTATE_ATTR(nr_hugepages_mempolicy);
  #endif
  
  
  static ssize_t nr_overcommit_hugepages_show(struct kobject *kobj,
                                          struct kobj_attribute *attr, char *buf)
  {
          struct hstate *h = kobj_to_hstate(kobj, NULL);
          return sprintf(buf, "%lu\n", h->nr_overcommit_huge_pages);
  }
  
  static ssize_t nr_overcommit_hugepages_store(struct kobject *kobj,
                  struct kobj_attribute *attr, const char *buf, size_t count)
  {
          int err;
          unsigned long input;
          struct hstate *h = kobj_to_hstate(kobj, NULL);
  
          if (h->order >= MAX_ORDER)
                  return -EINVAL;
  
          err = strict_strtoul(buf, 10, &input);
          if (err)
                  return err;
  
          spin_lock(&hugetlb_lock);
          h->nr_overcommit_huge_pages = input;
          spin_unlock(&hugetlb_lock);
  
          return count;
  }
  HSTATE_ATTR(nr_overcommit_hugepages);
  
  static ssize_t free_hugepages_show(struct kobject *kobj,
                                          struct kobj_attribute *attr, char *buf)
  {
          struct hstate *h;
          unsigned long free_huge_pages;
          int nid;
  
          h = kobj_to_hstate(kobj, &nid);
          if (nid == NUMA_NO_NODE)
                  free_huge_pages = h->free_huge_pages;
          else
                  free_huge_pages = h->free_huge_pages_node[nid];
  
          return sprintf(buf, "%lu\n", free_huge_pages);
  }
  HSTATE_ATTR_RO(free_hugepages);
  
  static ssize_t resv_hugepages_show(struct kobject *kobj,
                                          struct kobj_attribute *attr, char *buf)
  {
          struct hstate *h = kobj_to_hstate(kobj, NULL);
          return sprintf(buf, "%lu\n", h->resv_huge_pages);
  }
  HSTATE_ATTR_RO(resv_hugepages);
  
  static ssize_t surplus_hugepages_show(struct kobject *kobj,
                                          struct kobj_attribute *attr, char *buf)
  {
          struct hstate *h;
          unsigned long surplus_huge_pages;
          int nid;
  
          h = kobj_to_hstate(kobj, &nid);
          if (nid == NUMA_NO_NODE)
                  surplus_huge_pages = h->surplus_huge_pages;
          else
                  surplus_huge_pages = h->surplus_huge_pages_node[nid];
  
          return sprintf(buf, "%lu\n", surplus_huge_pages);
  }
  HSTATE_ATTR_RO(surplus_hugepages);
  
  static struct attribute *hstate_attrs[] = {
          &nr_hugepages_attr.attr,
          &nr_overcommit_hugepages_attr.attr,
          &free_hugepages_attr.attr,
          &resv_hugepages_attr.attr,
          &surplus_hugepages_attr.attr,
  #ifdef CONFIG_NUMA
          &nr_hugepages_mempolicy_attr.attr,
  #endif
          NULL,
  };
  
  static struct attribute_group hstate_attr_group = {
          .attrs = hstate_attrs,
  };
  
  static int hugetlb_sysfs_add_hstate(struct hstate *h, struct kobject *parent,
                                      struct kobject **hstate_kobjs,
                                      struct attribute_group *hstate_attr_group)
  {
          int retval;
          int hi = hstate_index(h);
  
          hstate_kobjs[hi] = kobject_create_and_add(h->name, parent);
          if (!hstate_kobjs[hi])
                  return -ENOMEM;
  
          retval = sysfs_create_group(hstate_kobjs[hi], hstate_attr_group);
          if (retval)
                  kobject_put(hstate_kobjs[hi]);
  
          return retval;
  }
  
  static void __init hugetlb_sysfs_init(void)
  {
          struct hstate *h;
          int err;
  
          hugepages_kobj = kobject_create_and_add("hugepages", mm_kobj);
          if (!hugepages_kobj)
                  return;
  
          for_each_hstate(h) {
                  err = hugetlb_sysfs_add_hstate(h, hugepages_kobj,
                                           hstate_kobjs, &hstate_attr_group);
                  if (err)
                          printk(KERN_ERR "Hugetlb: Unable to add hstate %s",
                                                                  h->name);
          }
  }
  
  #ifdef CONFIG_NUMA
  
  /*
   * node_hstate/s - associate per node hstate attributes, via their kobjects,
   * with node devices in node_devices[] using a parallel array.  The array
   * index of a node device or _hstate == node id.
   * This is here to avoid any static dependency of the node device driver, in
   * the base kernel, on the hugetlb module.
   */
  struct node_hstate {
          struct kobject          *hugepages_kobj;
          struct kobject          *hstate_kobjs[HUGE_MAX_HSTATE];
  };
  struct node_hstate node_hstates[MAX_NUMNODES];
  
  /*
   * A subset of global hstate attributes for node devices
   */
  static struct attribute *per_node_hstate_attrs[] = {
          &nr_hugepages_attr.attr,
          &free_hugepages_attr.attr,
          &surplus_hugepages_attr.attr,
          NULL,
  };
  
  static struct attribute_group per_node_hstate_attr_group = {
          .attrs = per_node_hstate_attrs,
  };
  
  /*
   * kobj_to_node_hstate - lookup global hstate for node device hstate attr kobj.
   * Returns node id via non-NULL nidp.
   */
  static struct hstate *kobj_to_node_hstate(struct kobject *kobj, int *nidp)
  {
          int nid;
  
          for (nid = 0; nid < nr_node_ids; nid++) {
                  struct node_hstate *nhs = &node_hstates[nid];
                  int i;
                  for (i = 0; i < HUGE_MAX_HSTATE; i++)
                          if (nhs->hstate_kobjs[i] == kobj) {
                                  if (nidp)
                                          *nidp = nid;
                                  return &hstates[i];
                          }
          }
  
          BUG();
          return NULL;
  }
  
  /*
   * Unregister hstate attributes from a single node device.
   * No-op if no hstate attributes attached.
   */
  void hugetlb_unregister_node(struct node *node)
  {
          struct hstate *h;
          struct node_hstate *nhs = &node_hstates[node->dev.id];
  
          if (!nhs->hugepages_kobj)
                  return;         /* no hstate attributes */
  
          for_each_hstate(h) {
                  int idx = hstate_index(h);
                  if (nhs->hstate_kobjs[idx]) {
                          kobject_put(nhs->hstate_kobjs[idx]);
                          nhs->hstate_kobjs[idx] = NULL;
                  }
          }
  
          kobject_put(nhs->hugepages_kobj);
          nhs->hugepages_kobj = NULL;
  }
  
  /*
   * hugetlb module exit:  unregister hstate attributes from node devices
   * that have them.
   */
  static void hugetlb_unregister_all_nodes(void)
  {
          int nid;
  
          /*
           * disable node device registrations.
           */
          register_hugetlbfs_with_node(NULL, NULL);
  
          /*
           * remove hstate attributes from any nodes that have them.
           */
          for (nid = 0; nid < nr_node_ids; nid++)
                  hugetlb_unregister_node(node_devices[nid]);
  }
  
  /*
   * Register hstate attributes for a single node device.
   * No-op if attributes already registered.
   */
  void hugetlb_register_node(struct node *node)
  {
          struct hstate *h;
          struct node_hstate *nhs = &node_hstates[node->dev.id];
          int err;
  
          if (nhs->hugepages_kobj)
                  return;         /* already allocated */
  
          nhs->hugepages_kobj = kobject_create_and_add("hugepages",
                                                          &node->dev.kobj);
          if (!nhs->hugepages_kobj)
                  return;
  
          for_each_hstate(h) {
                  err = hugetlb_sysfs_add_hstate(h, nhs->hugepages_kobj,
                                                  nhs->hstate_kobjs,
                                                  &per_node_hstate_attr_group);
                  if (err) {
                          printk(KERN_ERR "Hugetlb: Unable to add hstate %s"
                                          " for node %d\n",
                                                  h->name, node->dev.id);
                          hugetlb_unregister_node(node);
                          break;
                  }
          }
  }
  
  /*
   * hugetlb init time:  register hstate attributes for all registered node
   * devices of nodes that have memory.  All on-line nodes should have
   * registered their associated device by this time.
   */
  static void hugetlb_register_all_nodes(void)
  {
          int nid;
  
          for_each_node_state(nid, N_MEMORY) {
                  struct node *node = node_devices[nid];
                  if (node->dev.id == nid)
                          hugetlb_register_node(node);
          }
  
          /*
           * Let the node device driver know we're here so it can
           * [un]register hstate attributes on node hotplug.
           */
          register_hugetlbfs_with_node(hugetlb_register_node,
                                       hugetlb_unregister_node);
  }
  #else   /* !CONFIG_NUMA */
  
  static struct hstate *kobj_to_node_hstate(struct kobject *kobj, int *nidp)
  {
          BUG();
          if (nidp)
                  *nidp = -1;
          return NULL;
  }
  
  static void hugetlb_unregister_all_nodes(void) { }
  
  static void hugetlb_register_all_nodes(void) { }
  
  #endif
  
  static void __exit hugetlb_exit(void)
  {
          struct hstate *h;
  
          hugetlb_unregister_all_nodes();
  
          for_each_hstate(h) {
                  kobject_put(hstate_kobjs[hstate_index(h)]);
          }
  
          kobject_put(hugepages_kobj);
  }
  module_exit(hugetlb_exit);
  
  static int __init hugetlb_init(void)
  {
          /* Some platform decide whether they support huge pages at boot
           * time. On these, such as powerpc, HPAGE_SHIFT is set to 0 when
           * there is no such support
           */
          if (HPAGE_SHIFT == 0)
                  return 0;
  
          if (!size_to_hstate(default_hstate_size)) {
                  default_hstate_size = HPAGE_SIZE;
                  if (!size_to_hstate(default_hstate_size))
                          hugetlb_add_hstate(HUGETLB_PAGE_ORDER);
          }
          default_hstate_idx = hstate_index(size_to_hstate(default_hstate_size));
          if (default_hstate_max_huge_pages)
                  default_hstate.max_huge_pages = default_hstate_max_huge_pages;
  
          hugetlb_init_hstates();
          gather_bootmem_prealloc();
          report_hugepages();
  
          hugetlb_sysfs_init();
          hugetlb_register_all_nodes();
          hugetlb_cgroup_file_init();
  
          return 0;
  }
  module_init(hugetlb_init);
  
  /* Should be called on processing a hugepagesz=... option */
  void __init hugetlb_add_hstate(unsigned order)
  {
          struct hstate *h;
          unsigned long i;
  
          if (size_to_hstate(PAGE_SIZE << order)) {
                  printk(KERN_WARNING "hugepagesz= specified twice, ignoring\n");
                  return;
          }
          BUG_ON(hugetlb_max_hstate >= HUGE_MAX_HSTATE);
          BUG_ON(order == 0);
          h = &hstates[hugetlb_max_hstate++];
          h->order = order;
          h->mask = ~((1ULL << (order + PAGE_SHIFT)) - 1);
          h->nr_huge_pages = 0;
          h->free_huge_pages = 0;
          for (i = 0; i < MAX_NUMNODES; ++i)
                  INIT_LIST_HEAD(&h->hugepage_freelists[i]);
          INIT_LIST_HEAD(&h->hugepage_activelist);
          h->next_nid_to_alloc = first_node(node_states[N_MEMORY]);
          h->next_nid_to_free = first_node(node_states[N_MEMORY]);
          snprintf(h->name, HSTATE_NAME_LEN, "hugepages-%lukB",
                                          huge_page_size(h)/1024);
  
          parsed_hstate = h;
  }
  
  static int __init hugetlb_nrpages_setup(char *s)
  {
          unsigned long *mhp;
          static unsigned long *last_mhp;
  
          /*
           * !hugetlb_max_hstate means we haven't parsed a hugepagesz= parameter yet,
           * so this hugepages= parameter goes to the "default hstate".
           */
          if (!hugetlb_max_hstate)
                  mhp = &default_hstate_max_huge_pages;
          else
                  mhp = &parsed_hstate->max_huge_pages;
  
          if (mhp == last_mhp) {
                  printk(KERN_WARNING "hugepages= specified twice without "
                          "interleaving hugepagesz=, ignoring\n");
                  return 1;
          }
  
          if (sscanf(s, "%lu", mhp) <= 0)
                  *mhp = 0;
  
          /*
           * Global state is always initialized later in hugetlb_init.
           * But we need to allocate >= MAX_ORDER hstates here early to still
           * use the bootmem allocator.
           */
          if (hugetlb_max_hstate && parsed_hstate->order >= MAX_ORDER)
                  hugetlb_hstate_alloc_pages(parsed_hstate);
  
          last_mhp = mhp;
  
          return 1;
  }
  __setup("hugepages=", hugetlb_nrpages_setup);
  
  static int __init hugetlb_default_setup(char *s)
  {
          default_hstate_size = memparse(s, &s);
          return 1;
  }
  __setup("default_hugepagesz=", hugetlb_default_setup);
  
  static unsigned int cpuset_mems_nr(unsigned int *array)
  {
          int node;
          unsigned int nr = 0;
  
          for_each_node_mask(node, cpuset_current_mems_allowed)
                  nr += array[node];
  
          return nr;
  }
  
  #ifdef CONFIG_SYSCTL
  static int hugetlb_sysctl_handler_common(bool obey_mempolicy,
                           struct ctl_table *table, int write,
                           void __user *buffer, size_t *length, loff_t *ppos)
  {
          struct hstate *h = &default_hstate;
          unsigned long tmp;
          int ret;
  
          tmp = h->max_huge_pages;
  
          if (write && h->order >= MAX_ORDER)
                  return -EINVAL;
  
          table->data = &tmp;
          table->maxlen = sizeof(unsigned long);
          ret = proc_doulongvec_minmax(table, write, buffer, length, ppos);
          if (ret)
                  goto out;
  
          if (write) {
                  NODEMASK_ALLOC(nodemask_t, nodes_allowed,
                                                  GFP_KERNEL | __GFP_NORETRY);
                  if (!(obey_mempolicy &&
                                 init_nodemask_of_mempolicy(nodes_allowed))) {
                          NODEMASK_FREE(nodes_allowed);
                          nodes_allowed = &node_states[N_MEMORY];
                  }
                  h->max_huge_pages = set_max_huge_pages(h, tmp, nodes_allowed);
  
                  if (nodes_allowed != &node_states[N_MEMORY])
                          NODEMASK_FREE(nodes_allowed);
          }
  out:
          return ret;
  }
  
  int hugetlb_sysctl_handler(struct ctl_table *table, int write,
                            void __user *buffer, size_t *length, loff_t *ppos)
  {
  
          return hugetlb_sysctl_handler_common(false, table, write,
                                                          buffer, length, ppos);
  }
  
  #ifdef CONFIG_NUMA
  int hugetlb_mempolicy_sysctl_handler(struct ctl_table *table, int write,
                            void __user *buffer, size_t *length, loff_t *ppos)
  {
          return hugetlb_sysctl_handler_common(true, table, write,
                                                          buffer, length, ppos);
  }
  #endif /* CONFIG_NUMA */
  
  int hugetlb_treat_movable_handler(struct ctl_table *table, int write,
                          void __user *buffer,
                          size_t *length, loff_t *ppos)
  {
          proc_dointvec(table, write, buffer, length, ppos);
          if (hugepages_treat_as_movable)
                  htlb_alloc_mask = GFP_HIGHUSER_MOVABLE;
          else
                  htlb_alloc_mask = GFP_HIGHUSER;
          return 0;
  }
  
  int hugetlb_overcommit_handler(struct ctl_table *table, int write,
                          void __user *buffer,
                          size_t *length, loff_t *ppos)
  {
          struct hstate *h = &default_hstate;
          unsigned long tmp;
          int ret;
  
          tmp = h->nr_overcommit_huge_pages;
  
          if (write && h->order >= MAX_ORDER)
                  return -EINVAL;
  
          table->data = &tmp;
          table->maxlen = sizeof(unsigned long);
          ret = proc_doulongvec_minmax(table, write, buffer, length, ppos);
          if (ret)
                  goto out;
  
          if (write) {
                  spin_lock(&hugetlb_lock);
                  h->nr_overcommit_huge_pages = tmp;
                  spin_unlock(&hugetlb_lock);
          }
  out:
          return ret;
  }
  
  #endif /* CONFIG_SYSCTL */
  
  void hugetlb_report_meminfo(struct seq_file *m)
  {
          struct hstate *h = &default_hstate;
          seq_printf(m,
                          "HugePages_Total:   %5lu\n"
                          "HugePages_Free:    %5lu\n"
                          "HugePages_Rsvd:    %5lu\n"
                          "HugePages_Surp:    %5lu\n"
                          "Hugepagesize:   %8lu kB\n",
                          h->nr_huge_pages,
                          h->free_huge_pages,
                          h->resv_huge_pages,
                          h->surplus_huge_pages,
                          1UL << (huge_page_order(h) + PAGE_SHIFT - 10));
  }
  
  int hugetlb_report_node_meminfo(int nid, char *buf)
  {
          struct hstate *h = &default_hstate;
          return sprintf(buf,
                  "Node %d HugePages_Total: %5u\n"
                  "Node %d HugePages_Free:  %5u\n"
                  "Node %d HugePages_Surp:  %5u\n",
                  nid, h->nr_huge_pages_node[nid],
                  nid, h->free_huge_pages_node[nid],
                  nid, h->surplus_huge_pages_node[nid]);
  }
  
  /* Return the number pages of memory we physically have, in PAGE_SIZE units. */
  unsigned long hugetlb_total_pages(void)
  {
          struct hstate *h = &default_hstate;
          return h->nr_huge_pages * pages_per_huge_page(h);
  }
  
  static int hugetlb_acct_memory(struct hstate *h, long delta)
  {
          int ret = -ENOMEM;
  
          spin_lock(&hugetlb_lock);
          /*
           * When cpuset is configured, it breaks the strict hugetlb page
           * reservation as the accounting is done on a global variable. Such
           * reservation is completely rubbish in the presence of cpuset because
           * the reservation is not checked against page availability for the
           * current cpuset. Application can still potentially OOM'ed by kernel
           * with lack of free htlb page in cpuset that the task is in.
           * Attempt to enforce strict accounting with cpuset is almost
           * impossible (or too ugly) because cpuset is too fluid that
           * task or memory node can be dynamically moved between cpusets.
           *
           * The change of semantics for shared hugetlb mapping with cpuset is
           * undesirable. However, in order to preserve some of the semantics,
           * we fall back to check against current free page availability as
           * a best attempt and hopefully to minimize the impact of changing
           * semantics that cpuset has.
           */
          if (delta > 0) {
                  if (gather_surplus_pages(h, delta) < 0)
                          goto out;
  
                  if (delta > cpuset_mems_nr(h->free_huge_pages_node)) {
                          return_unused_surplus_pages(h, delta);
                          goto out;
                  }
          }
  
          ret = 0;
          if (delta < 0)
                  return_unused_surplus_pages(h, (unsigned long) -delta);
  
  out:
          spin_unlock(&hugetlb_lock);
          return ret;
  }
  
  static void hugetlb_vm_op_open(struct vm_area_struct *vma)
  {
          struct resv_map *reservations = vma_resv_map(vma);
  
          /*
           * This new VMA should share its siblings reservation map if present.
           * The VMA will only ever have a valid reservation map pointer where
           * it is being copied for another still existing VMA.  As that VMA
           * has a reference to the reservation map it cannot disappear until
           * after this open call completes.  It is therefore safe to take a
           * new reference here without additional locking.
           */
          if (reservations)
                  kref_get(&reservations->refs);
  }
  
  static void resv_map_put(struct vm_area_struct *vma)
  {
          struct resv_map *reservations = vma_resv_map(vma);
  
          if (!reservations)
                  return;
          kref_put(&reservations->refs, resv_map_release);
  }
  
  static void hugetlb_vm_op_close(struct vm_area_struct *vma)
  {
          struct hstate *h = hstate_vma(vma);
          struct resv_map *reservations = vma_resv_map(vma);
          struct hugepage_subpool *spool = subpool_vma(vma);
          unsigned long reserve;
          unsigned long start;
          unsigned long end;
  
          if (reservations) {
                  start = vma_hugecache_offset(h, vma, vma->vm_start);
                  end = vma_hugecache_offset(h, vma, vma->vm_end);
  
                  reserve = (end - start) -
                          region_count(&reservations->regions, start, end);
  
                  resv_map_put(vma);
  
                  if (reserve) {
                          hugetlb_acct_memory(h, -reserve);
                          hugepage_subpool_put_pages(spool, reserve);
                  }
          }
  }
  
  /*
   * We cannot handle pagefaults against hugetlb pages at all.  They cause
   * handle_mm_fault() to try to instantiate regular-sized pages in the
   * hugegpage VMA.  do_page_fault() is supposed to trap this, so BUG is we get
   * this far.
   */
  static int hugetlb_vm_op_fault(struct vm_area_struct *vma, struct vm_fault *vmf)
  {
          BUG();
          return 0;
  }
  
  const struct vm_operations_struct hugetlb_vm_ops = {
          .fault = hugetlb_vm_op_fault,
          .open = hugetlb_vm_op_open,
          .close = hugetlb_vm_op_close,
  };
  
  static pte_t make_huge_pte(struct vm_area_struct *vma, struct page *page,
                                  int writable)
  {
          pte_t entry;
  
          if (writable) {
                  entry =
                      pte_mkwrite(pte_mkdirty(mk_pte(page, vma->vm_page_prot)));
          } else {
                  entry = huge_pte_wrprotect(mk_pte(page, vma->vm_page_prot));
          }
          entry = pte_mkyoung(entry);
          entry = pte_mkhuge(entry);
          entry = arch_make_huge_pte(entry, vma, page, writable);
  
          return entry;
  }
  
  static void set_huge_ptep_writable(struct vm_area_struct *vma,
                                     unsigned long address, pte_t *ptep)
  {
          pte_t entry;
  
          entry = pte_mkwrite(pte_mkdirty(huge_ptep_get(ptep)));
          if (huge_ptep_set_access_flags(vma, address, ptep, entry, 1))
                  update_mmu_cache(vma, address, ptep);
  }
  
  
  int copy_hugetlb_page_range(struct mm_struct *dst, struct mm_struct *src,
                              struct vm_area_struct *vma)
  {
          pte_t *src_pte, *dst_pte, entry;
          struct page *ptepage;
          unsigned long addr;
          int cow;
          struct hstate *h = hstate_vma(vma);
          unsigned long sz = huge_page_size(h);
  
          cow = (vma->vm_flags & (VM_SHARED | VM_MAYWRITE)) == VM_MAYWRITE;
  
          for (addr = vma->vm_start; addr < vma->vm_end; addr += sz) {
                  src_pte = huge_pte_offset(src, addr);
                  if (!src_pte)
                          continue;
                  dst_pte = huge_pte_alloc(dst, addr, sz);
                  if (!dst_pte)
                          goto nomem;
  
                  /* If the pagetables are shared don't copy or take references */
                  if (dst_pte == src_pte)
                          continue;
  
                  spin_lock(&dst->page_table_lock);
                  spin_lock_nested(&src->page_table_lock, SINGLE_DEPTH_NESTING);
                  if (!huge_pte_none(huge_ptep_get(src_pte))) {
                          if (cow)
                                  huge_ptep_set_wrprotect(src, addr, src_pte);
                          entry = huge_ptep_get(src_pte);
                          ptepage = pte_page(entry);
                          get_page(ptepage);
                          page_dup_rmap(ptepage);
                          set_huge_pte_at(dst, addr, dst_pte, entry);
                  }
                  spin_unlock(&src->page_table_lock);
                  spin_unlock(&dst->page_table_lock);
          }
          return 0;
  
  nomem:
          return -ENOMEM;
  }
  
  static int is_hugetlb_entry_migration(pte_t pte)
  {
          swp_entry_t swp;
  
          if (huge_pte_none(pte) || pte_present(pte))
                  return 0;
          swp = pte_to_swp_entry(pte);
          if (non_swap_entry(swp) && is_migration_entry(swp))
                  return 1;
          else
                  return 0;
  }
  
  static int is_hugetlb_entry_hwpoisoned(pte_t pte)
  {
          swp_entry_t swp;
  
          if (huge_pte_none(pte) || pte_present(pte))
                  return 0;
          swp = pte_to_swp_entry(pte);
          if (non_swap_entry(swp) && is_hwpoison_entry(swp))
                  return 1;
          else
                  return 0;
  }
  
  void __unmap_hugepage_range(struct mmu_gather *tlb, struct vm_area_struct *vma,
                              unsigned long start, unsigned long end,
                              struct page *ref_page)
  {
          int force_flush = 0;
          struct mm_struct *mm = vma->vm_mm;
          unsigned long address;
          pte_t *ptep;
          pte_t pte;
          struct page *page;
          struct hstate *h = hstate_vma(vma);
          unsigned long sz = huge_page_size(h);
          const unsigned long mmun_start = start; /* For mmu_notifiers */
          const unsigned long mmun_end   = end;   /* For mmu_notifiers */
  
          WARN_ON(!is_vm_hugetlb_page(vma));
          BUG_ON(start & ~huge_page_mask(h));
          BUG_ON(end & ~huge_page_mask(h));
  
          tlb_start_vma(tlb, vma);
          mmu_notifier_invalidate_range_start(mm, mmun_start, mmun_end);
  again:
          spin_lock(&mm->page_table_lock);
          for (address = start; address < end; address += sz) {
                  ptep = huge_pte_offset(mm, address);
                  if (!ptep)
                          continue;
  
                  if (huge_pmd_unshare(mm, &address, ptep))
                          continue;
  
                  pte = huge_ptep_get(ptep);
                  if (huge_pte_none(pte))
                          continue;
  
                  /*
                   * HWPoisoned hugepage is already unmapped and dropped reference
                   */
                  if (unlikely(is_hugetlb_entry_hwpoisoned(pte))) {
                          pte_clear(mm, address, ptep);
                          continue;
                  }
  
                  page = pte_page(pte);
                  /*
                   * If a reference page is supplied, it is because a specific
                   * page is being unmapped, not a range. Ensure the page we
                   * are about to unmap is the actual page of interest.
                   */
                  if (ref_page) {
                          if (page != ref_page)
                                  continue;
  
                          /*
                           * Mark the VMA as having unmapped its page so that
                           * future faults in this VMA will fail rather than
                           * looking like data was lost
                           */
                          set_vma_resv_flags(vma, HPAGE_RESV_UNMAPPED);
                  }
  
                  pte = huge_ptep_get_and_clear(mm, address, ptep);
                  tlb_remove_tlb_entry(tlb, ptep, address);
                  if (pte_dirty(pte))
                          set_page_dirty(page);
  
                  page_remove_rmap(page);
                  force_flush = !__tlb_remove_page(tlb, page);
                  if (force_flush)
                          break;
                  /* Bail out after unmapping reference page if supplied */
                  if (ref_page)
                          break;
          }
          spin_unlock(&mm->page_table_lock);
          /*
           * mmu_gather ran out of room to batch pages, we break out of
           * the PTE lock to avoid doing the potential expensive TLB invalidate
           * and page-free while holding it.
           */
          if (force_flush) {
                  force_flush = 0;
                  tlb_flush_mmu(tlb);
                  if (address < end && !ref_page)
                          goto again;
          }
          mmu_notifier_invalidate_range_end(mm, mmun_start, mmun_end);
          tlb_end_vma(tlb, vma);
  }
  
  void __unmap_hugepage_range_final(struct mmu_gather *tlb,
                            struct vm_area_struct *vma, unsigned long start,
                            unsigned long end, struct page *ref_page)
  {
          __unmap_hugepage_range(tlb, vma, start, end, ref_page);
  
          /*
           * Clear this flag so that x86's huge_pmd_share page_table_shareable
           * test will fail on a vma being torn down, and not grab a page table
           * on its way out.  We're lucky that the flag has such an appropriate
           * name, and can in fact be safely cleared here. We could clear it
           * before the __unmap_hugepage_range above, but all that's necessary
           * is to clear it before releasing the i_mmap_mutex. This works
           * because in the context this is called, the VMA is about to be
           * destroyed and the i_mmap_mutex is held.
           */
          vma->vm_flags &= ~VM_MAYSHARE;
  }
  
  void unmap_hugepage_range(struct vm_area_struct *vma, unsigned long start,
                            unsigned long end, struct page *ref_page)
  {
          struct mm_struct *mm;
          struct mmu_gather tlb;
  
          mm = vma->vm_mm;
  
          tlb_gather_mmu(&tlb, mm, 0);
          __unmap_hugepage_range(&tlb, vma, start, end, ref_page);
          tlb_finish_mmu(&tlb, start, end);
  }
  
  /*
   * This is called when the original mapper is failing to COW a MAP_PRIVATE
   * mappping it owns the reserve page for. The intention is to unmap the page
   * from other VMAs and let the children be SIGKILLed if they are faulting the
   * same region.
   */
  static int unmap_ref_private(struct mm_struct *mm, struct vm_area_struct *vma,
                                  struct page *page, unsigned long address)
  {
          struct hstate *h = hstate_vma(vma);
          struct vm_area_struct *iter_vma;
          struct address_space *mapping;
          pgoff_t pgoff;
  
          /*
           * vm_pgoff is in PAGE_SIZE units, hence the different calculation
           * from page cache lookup which is in HPAGE_SIZE units.
           */
          address = address & huge_page_mask(h);
          pgoff = ((address - vma->vm_start) >> PAGE_SHIFT) +
                          vma->vm_pgoff;
          mapping = vma->vm_file->f_dentry->d_inode->i_mapping;
  
          /*
           * Take the mapping lock for the duration of the table walk. As
           * this mapping should be shared between all the VMAs,
           * __unmap_hugepage_range() is called as the lock is already held
           */
          mutex_lock(&mapping->i_mmap_mutex);
          vma_interval_tree_foreach(iter_vma, &mapping->i_mmap, pgoff, pgoff) {
                  /* Do not unmap the current VMA */
                  if (iter_vma == vma)
                          continue;
  
                  /*
                   * Unmap the page from other VMAs without their own reserves.
                   * They get marked to be SIGKILLed if they fault in these
                   * areas. This is because a future no-page fault on this VMA
                   * could insert a zeroed page instead of the data existing
                   * from the time of fork. This would look like data corruption
                   */
                  if (!is_vma_resv_set(iter_vma, HPAGE_RESV_OWNER))
                          unmap_hugepage_range(iter_vma, address,
                                               address + huge_page_size(h), page);
          }
          mutex_unlock(&mapping->i_mmap_mutex);
  
          return 1;
  }
  
  /*
   * Hugetlb_cow() should be called with page lock of the original hugepage held.
   * Called with hugetlb_instantiation_mutex held and pte_page locked so we
   * cannot race with other handlers or page migration.
   * Keep the pte_same checks anyway to make transition from the mutex easier.
   */
  static int hugetlb_cow(struct mm_struct *mm, struct vm_area_struct *vma,
                          unsigned long address, pte_t *ptep, pte_t pte,
                          struct page *pagecache_page)
  {
          struct hstate *h = hstate_vma(vma);
          struct page *old_page, *new_page;
          int avoidcopy;
          int outside_reserve = 0;
          unsigned long mmun_start;       /* For mmu_notifiers */
          unsigned long mmun_end;         /* For mmu_notifiers */
  
          old_page = pte_page(pte);
  
  retry_avoidcopy:
          /* If no-one else is actually using this page, avoid the copy
           * and just make the page writable */
          avoidcopy = (page_mapcount(old_page) == 1);
          if (avoidcopy) {
                  if (PageAnon(old_page))
                          page_move_anon_rmap(old_page, vma, address);
                  set_huge_ptep_writable(vma, address, ptep);
                  return 0;
          }
  
          /*
           * If the process that created a MAP_PRIVATE mapping is about to
           * perform a COW due to a shared page count, attempt to satisfy
           * the allocation without using the existing reserves. The pagecache
           * page is used to determine if the reserve at this address was
           * consumed or not. If reserves were used, a partial faulted mapping
           * at the time of fork() could consume its reserves on COW instead
           * of the full address range.
           */
          if (!(vma->vm_flags & VM_MAYSHARE) &&
                          is_vma_resv_set(vma, HPAGE_RESV_OWNER) &&
                          old_page != pagecache_page)
                  outside_reserve = 1;
  
          page_cache_get(old_page);
  
          /* Drop page_table_lock as buddy allocator may be called */
          spin_unlock(&mm->page_table_lock);
          new_page = alloc_huge_page(vma, address, outside_reserve);
  
          if (IS_ERR(new_page)) {
                  long err = PTR_ERR(new_page);
                  page_cache_release(old_page);
  
                  /*
                   * If a process owning a MAP_PRIVATE mapping fails to COW,
                   * it is due to references held by a child and an insufficient
                   * huge page pool. To guarantee the original mappers
                   * reliability, unmap the page from child processes. The child
                   * may get SIGKILLed if it later faults.
                   */
                  if (outside_reserve) {
                          BUG_ON(huge_pte_none(pte));
                          if (unmap_ref_private(mm, vma, old_page, address)) {
                                  BUG_ON(huge_pte_none(pte));
                                  spin_lock(&mm->page_table_lock);
                                  ptep = huge_pte_offset(mm, address & huge_page_mask(h));
                                  if (likely(pte_same(huge_ptep_get(ptep), pte)))
                                          goto retry_avoidcopy;
                                  /*
                                   * race occurs while re-acquiring page_table_lock, and
                                   * our job is done.
                                   */
                                  return 0;
                          }
                          WARN_ON_ONCE(1);
                  }
  
                  /* Caller expects lock to be held */
                  spin_lock(&mm->page_table_lock);
                  if (err == -ENOMEM)
                          return VM_FAULT_OOM;
                  else
                          return VM_FAULT_SIGBUS;
          }
  
          /*
           * When the original hugepage is shared one, it does not have
           * anon_vma prepared.
           */
          if (unlikely(anon_vma_prepare(vma))) {
                  page_cache_release(new_page);
                  page_cache_release(old_page);
                  /* Caller expects lock to be held */
                  spin_lock(&mm->page_table_lock);
                  return VM_FAULT_OOM;
          }
  
          copy_user_huge_page(new_page, old_page, address, vma,
                              pages_per_huge_page(h));
          __SetPageUptodate(new_page);
  
          mmun_start = address & huge_page_mask(h);
          mmun_end = mmun_start + huge_page_size(h);
          mmu_notifier_invalidate_range_start(mm, mmun_start, mmun_end);
          /*
           * Retake the page_table_lock to check for racing updates
           * before the page tables are altered
           */
          spin_lock(&mm->page_table_lock);
          ptep = huge_pte_offset(mm, address & huge_page_mask(h));
          if (likely(pte_same(huge_ptep_get(ptep), pte))) {
                  /* Break COW */
                  huge_ptep_clear_flush(vma, address, ptep);
                  set_huge_pte_at(mm, address, ptep,
                                  make_huge_pte(vma, new_page, 1));
                  page_remove_rmap(old_page);
                  hugepage_add_new_anon_rmap(new_page, vma, address);
                  /* Make the old page be freed below */
                  new_page = old_page;
          }
          spin_unlock(&mm->page_table_lock);
          mmu_notifier_invalidate_range_end(mm, mmun_start, mmun_end);
          /* Caller expects lock to be held */
          spin_lock(&mm->page_table_lock);
          page_cache_release(new_page);
          page_cache_release(old_page);
          return 0;
  }
  
  /* Return the pagecache page at a given address within a VMA */
  static struct page *hugetlbfs_pagecache_page(struct hstate *h,
                          struct vm_area_struct *vma, unsigned long address)
  {
          struct address_space *mapping;
          pgoff_t idx;
  
          mapping = vma->vm_file->f_mapping;
          idx = vma_hugecache_offset(h, vma, address);
  
          return find_lock_page(mapping, idx);
  }
  
  /*
   * Return whether there is a pagecache page to back given address within VMA.
   * Caller follow_hugetlb_page() holds page_table_lock so we cannot lock_page.
   */
  static bool hugetlbfs_pagecache_present(struct hstate *h,
                          struct vm_area_struct *vma, unsigned long address)
  {
          struct address_space *mapping;
          pgoff_t idx;
          struct page *page;
  
          mapping = vma->vm_file->f_mapping;
          idx = vma_hugecache_offset(h, vma, address);
  
          page = find_get_page(mapping, idx);
          if (page)
                  put_page(page);
          return page != NULL;
  }
  
  static int hugetlb_no_page(struct mm_struct *mm, struct vm_area_struct *vma,
                          unsigned long address, pte_t *ptep, unsigned int flags)
  {
          struct hstate *h = hstate_vma(vma);
          int ret = VM_FAULT_SIGBUS;
          int anon_rmap = 0;
          pgoff_t idx;
          unsigned long size;
          struct page *page;
          struct address_space *mapping;
          pte_t new_pte;
  
          /*
           * Currently, we are forced to kill the process in the event the
           * original mapper has unmapped pages from the child due to a failed
           * COW. Warn that such a situation has occurred as it may not be obvious
           */
          if (is_vma_resv_set(vma, HPAGE_RESV_UNMAPPED)) {
                  printk(KERN_WARNING
                          "PID %d killed due to inadequate hugepage pool\n",
                          current->pid);
                  return ret;
          }
  
          mapping = vma->vm_file->f_mapping;
          idx = vma_hugecache_offset(h, vma, address);
  
          /*
           * Use page lock to guard against racing truncation
           * before we get page_table_lock.
           */
  retry:
          page = find_lock_page(mapping, idx);
          if (!page) {
                  size = i_size_read(mapping->host) >> huge_page_shift(h);
                  if (idx >= size)
                          goto out;
                  page = alloc_huge_page(vma, address, 0);
                  if (IS_ERR(page)) {
                          ret = PTR_ERR(page);
                          if (ret == -ENOMEM)
                                  ret = VM_FAULT_OOM;
                          else
                                  ret = VM_FAULT_SIGBUS;
                          goto out;
                  }
                  clear_huge_page(page, address, pages_per_huge_page(h));
                  __SetPageUptodate(page);
  
                  if (vma->vm_flags & VM_MAYSHARE) {
                          int err;
                          struct inode *inode = mapping->host;
  
                          err = add_to_page_cache(page, mapping, idx, GFP_KERNEL);
                          if (err) {
                                  put_page(page);
                                  if (err == -EEXIST)
                                          goto retry;
                                  goto out;
                          }
  
                          spin_lock(&inode->i_lock);
                          inode->i_blocks += blocks_per_huge_page(h);
                          spin_unlock(&inode->i_lock);
                  } else {
                          lock_page(page);
                          if (unlikely(anon_vma_prepare(vma))) {
                                  ret = VM_FAULT_OOM;
                                  goto backout_unlocked;
                          }
                          anon_rmap = 1;
                  }
          } else {
                  /*
                   * If memory error occurs between mmap() and fault, some process
                   * don't have hwpoisoned swap entry for errored virtual address.
                   * So we need to block hugepage fault by PG_hwpoison bit check.
                   */
                  if (unlikely(PageHWPoison(page))) {
                          ret = VM_FAULT_HWPOISON |
                                  VM_FAULT_SET_HINDEX(hstate_index(h));
                          goto backout_unlocked;
                  }
          }
  
          /*
           * If we are going to COW a private mapping later, we examine the
           * pending reservations for this page now. This will ensure that
           * any allocations necessary to record that reservation occur outside
           * the spinlock.
           */
          if ((flags & FAULT_FLAG_WRITE) && !(vma->vm_flags & VM_SHARED))
                  if (vma_needs_reservation(h, vma, address) < 0) {
                          ret = VM_FAULT_OOM;
                          goto backout_unlocked;
                  }
  
          spin_lock(&mm->page_table_lock);
          size = i_size_read(mapping->host) >> huge_page_shift(h);
          if (idx >= size)
                  goto backout;
  
          ret = 0;
          if (!huge_pte_none(huge_ptep_get(ptep)))
                  goto backout;
  
          if (anon_rmap)
                  hugepage_add_new_anon_rmap(page, vma, address);
          else
                  page_dup_rmap(page);
          new_pte = make_huge_pte(vma, page, ((vma->vm_flags & VM_WRITE)
                                  && (vma->vm_flags & VM_SHARED)));
          set_huge_pte_at(mm, address, ptep, new_pte);
  
          if ((flags & FAULT_FLAG_WRITE) && !(vma->vm_flags & VM_SHARED)) {
                  /* Optimization, do the COW without a second fault */
                  ret = hugetlb_cow(mm, vma, address, ptep, new_pte, page);
          }
  
          spin_unlock(&mm->page_table_lock);
          unlock_page(page);
  out:
          return ret;
  
  backout:
          spin_unlock(&mm->page_table_lock);
  backout_unlocked:
          unlock_page(page);
          put_page(page);
          goto out;
  }
  
  int hugetlb_fault(struct mm_struct *mm, struct vm_area_struct *vma,
                          unsigned long address, unsigned int flags)
  {
          pte_t *ptep;
          pte_t entry;
          int ret;
          struct page *page = NULL;
          struct page *pagecache_page = NULL;
          static DEFINE_MUTEX(hugetlb_instantiation_mutex);
          struct hstate *h = hstate_vma(vma);
  
          address &= huge_page_mask(h);
  
          ptep = huge_pte_offset(mm, address);
          if (ptep) {
                  entry = huge_ptep_get(ptep);
                  if (unlikely(is_hugetlb_entry_migration(entry))) {
                          migration_entry_wait(mm, (pmd_t *)ptep, address);
                          return 0;
                  } else if (unlikely(is_hugetlb_entry_hwpoisoned(entry)))
                          return VM_FAULT_HWPOISON_LARGE |
                                  VM_FAULT_SET_HINDEX(hstate_index(h));
          }
  
          ptep = huge_pte_alloc(mm, address, huge_page_size(h));
          if (!ptep)
                  return VM_FAULT_OOM;
  
          /*
           * Serialize hugepage allocation and instantiation, so that we don't
           * get spurious allocation failures if two CPUs race to instantiate
           * the same page in the page cache.
           */
          mutex_lock(&hugetlb_instantiation_mutex);
          entry = huge_ptep_get(ptep);
          if (huge_pte_none(entry)) {
                  ret = hugetlb_no_page(mm, vma, address, ptep, flags);
                  goto out_mutex;
          }
  
          ret = 0;
  
          /*
           * If we are going to COW the mapping later, we examine the pending
           * reservations for this page now. This will ensure that any
           * allocations necessary to record that reservation occur outside the
           * spinlock. For private mappings, we also lookup the pagecache
           * page now as it is used to determine if a reservation has been
           * consumed.
           */
          if ((flags & FAULT_FLAG_WRITE) && !pte_write(entry)) {
                  if (vma_needs_reservation(h, vma, address) < 0) {
                          ret = VM_FAULT_OOM;
                          goto out_mutex;
                  }
  
                  if (!(vma->vm_flags & VM_MAYSHARE))
                          pagecache_page = hugetlbfs_pagecache_page(h,
                                                                  vma, address);
          }
  
          /*
           * hugetlb_cow() requires page locks of pte_page(entry) and
           * pagecache_page, so here we need take the former one
           * when page != pagecache_page or !pagecache_page.
           * Note that locking order is always pagecache_page -> page,
           * so no worry about deadlock.
           */
          page = pte_page(entry);
          get_page(page);
          if (page != pagecache_page)
                  lock_page(page);
  
          spin_lock(&mm->page_table_lock);
          /* Check for a racing update before calling hugetlb_cow */
          if (unlikely(!pte_same(entry, huge_ptep_get(ptep))))
                  goto out_page_table_lock;
  
  
          if (flags & FAULT_FLAG_WRITE) {
                  if (!pte_write(entry)) {
                          ret = hugetlb_cow(mm, vma, address, ptep, entry,
                                                          pagecache_page);
                          goto out_page_table_lock;
                  }
                  entry = pte_mkdirty(entry);
          }
          entry = pte_mkyoung(entry);
          if (huge_ptep_set_access_flags(vma, address, ptep, entry,
                                                  flags & FAULT_FLAG_WRITE))
                  update_mmu_cache(vma, address, ptep);
  
  out_page_table_lock:
          spin_unlock(&mm->page_table_lock);
  
          if (pagecache_page) {
                  unlock_page(pagecache_page);
                  put_page(pagecache_page);
          }
          if (page != pagecache_page)
                  unlock_page(page);
          put_page(page);
  
  out_mutex:
          mutex_unlock(&hugetlb_instantiation_mutex);
  
          return ret;
  }
  
  /* Can be overriden by architectures */
  __attribute__((weak)) struct page *
  follow_huge_pud(struct mm_struct *mm, unsigned long address,
                 pud_t *pud, int write)
  {
          BUG();
          return NULL;
  }
  
  int follow_hugetlb_page(struct mm_struct *mm, struct vm_area_struct *vma,
                          struct page **pages, struct vm_area_struct **vmas,
                          unsigned long *position, int *length, int i,
                          unsigned int flags)
  {
          unsigned long pfn_offset;
          unsigned long vaddr = *position;
          int remainder = *length;
          struct hstate *h = hstate_vma(vma);
  
          spin_lock(&mm->page_table_lock);
          while (vaddr < vma->vm_end && remainder) {
                  pte_t *pte;
                  int absent;
                  struct page *page;
  
                  /*
                   * Some archs (sparc64, sh*) have multiple pte_ts to
                   * each hugepage.  We have to make sure we get the
                   * first, for the page indexing below to work.
                   */
                  pte = huge_pte_offset(mm, vaddr & huge_page_mask(h));
                  absent = !pte || huge_pte_none(huge_ptep_get(pte));
  
                  /*
                   * When coredumping, it suits get_dump_page if we just return
                   * an error where there's an empty slot with no huge pagecache
                   * to back it.  This way, we avoid allocating a hugepage, and
                   * the sparse dumpfile avoids allocating disk blocks, but its
                   * huge holes still show up with zeroes where they need to be.
                   */
                  if (absent && (flags & FOLL_DUMP) &&
                      !hugetlbfs_pagecache_present(h, vma, vaddr)) {
                          remainder = 0;
                          break;
                  }
  
                  if (absent ||
                      ((flags & FOLL_WRITE) && !pte_write(huge_ptep_get(pte)))) {
                          int ret;
  
                          spin_unlock(&mm->page_table_lock);
                          ret = hugetlb_fault(mm, vma, vaddr,
                                  (flags & FOLL_WRITE) ? FAULT_FLAG_WRITE : 0);
                          spin_lock(&mm->page_table_lock);
                          if (!(ret & VM_FAULT_ERROR))
                                  continue;
  
                          remainder = 0;
                          break;
                  }
  
                  pfn_offset = (vaddr & ~huge_page_mask(h)) >> PAGE_SHIFT;
                  page = pte_page(huge_ptep_get(pte));
  same_page:
                  if (pages) {
                          pages[i] = mem_map_offset(page, pfn_offset);
                          get_page(pages[i]);
                  }
  
                  if (vmas)
                          vmas[i] = vma;
  
                  vaddr += PAGE_SIZE;
                  ++pfn_offset;
                  --remainder;
                  ++i;
                  if (vaddr < vma->vm_end && remainder &&
                                  pfn_offset < pages_per_huge_page(h)) {
                          /*
                           * We use pfn_offset to avoid touching the pageframes
                           * of this compound page.
                           */
                          goto same_page;
                  }
          }
          spin_unlock(&mm->page_table_lock);
          *length = remainder;
          *position = vaddr;
  
          return i ? i : -EFAULT;
  }
  
  unsigned long hugetlb_change_protection(struct vm_area_struct *vma,
                  unsigned long address, unsigned long end, pgprot_t newprot)
  {
          struct mm_struct *mm = vma->vm_mm;
          unsigned long start = address;
          pte_t *ptep;
          pte_t pte;
          struct hstate *h = hstate_vma(vma);
          unsigned long pages = 0;
  
          BUG_ON(address >= end);
          flush_cache_range(vma, address, end);
  
          mutex_lock(&vma->vm_file->f_mapping->i_mmap_mutex);
          spin_lock(&mm->page_table_lock);
          for (; address < end; address += huge_page_size(h)) {
                  ptep = huge_pte_offset(mm, address);
                  if (!ptep)
                          continue;
                  if (huge_pmd_unshare(mm, &address, ptep)) {
                          pages++;
                          continue;
                  }
                  if (!huge_pte_none(huge_ptep_get(ptep))) {
                          pte = huge_ptep_get_and_clear(mm, address, ptep);
                          pte = pte_mkhuge(pte_modify(pte, newprot));
                          set_huge_pte_at(mm, address, ptep, pte);
                          pages++;
                  }
          }
          spin_unlock(&mm->page_table_lock);
          /*
           * Must flush TLB before releasing i_mmap_mutex: x86's huge_pmd_unshare
           * may have cleared our pud entry and done put_page on the page table:
           * once we release i_mmap_mutex, another task can do the final put_page
           * and that page table be reused and filled with junk.
           */
          flush_tlb_range(vma, start, end);
          mutex_unlock(&vma->vm_file->f_mapping->i_mmap_mutex);
  
          return pages << h->order;
  }
  
  int hugetlb_reserve_pages(struct inode *inode,
                                          long from, long to,
                                          struct vm_area_struct *vma,
                                          vm_flags_t vm_flags)
  {
          long ret, chg;
          struct hstate *h = hstate_inode(inode);
          struct hugepage_subpool *spool = subpool_inode(inode);
  
          /*
           * Only apply hugepage reservation if asked. At fault time, an
           * attempt will be made for VM_NORESERVE to allocate a page
           * without using reserves
           */
          if (vm_flags & VM_NORESERVE)
                  return 0;
  
          /*
           * Shared mappings base their reservation on the number of pages that
           * are already allocated on behalf of the file. Private mappings need
           * to reserve the full area even if read-only as mprotect() may be
           * called to make the mapping read-write. Assume !vma is a shm mapping
           */
          if (!vma || vma->vm_flags & VM_MAYSHARE)
                  chg = region_chg(&inode->i_mapping->private_list, from, to);
          else {
                  struct resv_map *resv_map = resv_map_alloc();
                  if (!resv_map)
                          return -ENOMEM;
  
                  chg = to - from;
  
                  set_vma_resv_map(vma, resv_map);
                  set_vma_resv_flags(vma, HPAGE_RESV_OWNER);
          }
  
          if (chg < 0) {
                  ret = chg;
                  goto out_err;
          }
  
          /* There must be enough pages in the subpool for the mapping */
          if (hugepage_subpool_get_pages(spool, chg)) {
                  ret = -ENOSPC;
                  goto out_err;
          }
  
          /*
           * Check enough hugepages are available for the reservation.
           * Hand the pages back to the subpool if there are not
           */
          ret = hugetlb_acct_memory(h, chg);
          if (ret < 0) {
                  hugepage_subpool_put_pages(spool, chg);
                  goto out_err;
          }
  
          /*
           * Account for the reservations made. Shared mappings record regions
           * that have reservations as they are shared by multiple VMAs.
           * When the last VMA disappears, the region map says how much
           * the reservation was and the page cache tells how much of
           * the reservation was consumed. Private mappings are per-VMA and
           * only the consumed reservations are tracked. When the VMA
           * disappears, the original reservation is the VMA size and the
           * consumed reservations are stored in the map. Hence, nothing
           * else has to be done for private mappings here
           */
          if (!vma || vma->vm_flags & VM_MAYSHARE)
                  region_add(&inode->i_mapping->private_list, from, to);
          return 0;
  out_err:
          if (vma)
                  resv_map_put(vma);
          return ret;
  }
  
  void hugetlb_unreserve_pages(struct inode *inode, long offset, long freed)
  {
          struct hstate *h = hstate_inode(inode);
          long chg = region_truncate(&inode->i_mapping->private_list, offset);
          struct hugepage_subpool *spool = subpool_inode(inode);
  
          spin_lock(&inode->i_lock);
          inode->i_blocks -= (blocks_per_huge_page(h) * freed);
          spin_unlock(&inode->i_lock);
  
          hugepage_subpool_put_pages(spool, (chg - freed));
          hugetlb_acct_memory(h, -(chg - freed));
  }
  
  #ifdef CONFIG_MEMORY_FAILURE
  
  /* Should be called in hugetlb_lock */
  static int is_hugepage_on_freelist(struct page *hpage)
  {
          struct page *page;
          struct page *tmp;
          struct hstate *h = page_hstate(hpage);
          int nid = page_to_nid(hpage);
  
          list_for_each_entry_safe(page, tmp, &h->hugepage_freelists[nid], lru)
                  if (page == hpage)
                          return 1;
          return 0;
  }
  
  /*
   * This function is called from memory failure code.
   * Assume the caller holds page lock of the head page.
   */
  int dequeue_hwpoisoned_huge_page(struct page *hpage)
  {
          struct hstate *h = page_hstate(hpage);
          int nid = page_to_nid(hpage);
          int ret = -EBUSY;
  
          spin_lock(&hugetlb_lock);
          if (is_hugepage_on_freelist(hpage)) {
                  /*
                   * Hwpoisoned hugepage isn't linked to activelist or freelist,
                   * but dangling hpage->lru can trigger list-debug warnings
                   * (this happens when we call unpoison_memory() on it),
                   * so let it point to itself with list_del_init().
                   */
                  list_del_init(&hpage->lru);
                  set_page_refcounted(hpage);
                  h->free_huge_pages--;
                  h->free_huge_pages_node[nid]--;
                  ret = 0;
          }
          spin_unlock(&hugetlb_lock);
          return ret;
  }
  #endif

Cache object: a7c59346d1687e9b6eb5196a8dad8ad5