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

     /*
      * SLOB Allocator: Simple List Of Blocks
      *
      * Matt Mackall <mpm@selenic.com> 12/30/03
      *
      * NUMA support by Paul Mundt, 2007.
      *
      * How SLOB works:
      *
     * The core of SLOB is a traditional K&R style heap allocator, with
     * support for returning aligned objects. The granularity of this
     * allocator is as little as 2 bytes, however typically most architectures
     * will require 4 bytes on 32-bit and 8 bytes on 64-bit.
     *
     * The slob heap is a set of linked list of pages from alloc_pages(),
     * and within each page, there is a singly-linked list of free blocks
     * (slob_t). The heap is grown on demand. To reduce fragmentation,
     * heap pages are segregated into three lists, with objects less than
     * 256 bytes, objects less than 1024 bytes, and all other objects.
     *
     * Allocation from heap involves first searching for a page with
     * sufficient free blocks (using a next-fit-like approach) followed by
     * a first-fit scan of the page. Deallocation inserts objects back
     * into the free list in address order, so this is effectively an
     * address-ordered first fit.
     *
     * Above this is an implementation of kmalloc/kfree. Blocks returned
     * from kmalloc are prepended with a 4-byte header with the kmalloc size.
     * If kmalloc is asked for objects of PAGE_SIZE or larger, it calls
     * alloc_pages() directly, allocating compound pages so the page order
     * does not have to be separately tracked.
     * These objects are detected in kfree() because PageSlab()
     * is false for them.
     *
     * SLAB is emulated on top of SLOB by simply calling constructors and
     * destructors for every SLAB allocation. Objects are returned with the
     * 4-byte alignment unless the SLAB_HWCACHE_ALIGN flag is set, in which
     * case the low-level allocator will fragment blocks to create the proper
     * alignment. Again, objects of page-size or greater are allocated by
     * calling alloc_pages(). As SLAB objects know their size, no separate
     * size bookkeeping is necessary and there is essentially no allocation
     * space overhead, and compound pages aren't needed for multi-page
     * allocations.
     *
     * NUMA support in SLOB is fairly simplistic, pushing most of the real
     * logic down to the page allocator, and simply doing the node accounting
     * on the upper levels. In the event that a node id is explicitly
     * provided, alloc_pages_exact_node() with the specified node id is used
     * instead. The common case (or when the node id isn't explicitly provided)
     * will default to the current node, as per numa_node_id().
     *
     * Node aware pages are still inserted in to the global freelist, and
     * these are scanned for by matching against the node id encoded in the
     * page flags. As a result, block allocations that can be satisfied from
     * the freelist will only be done so on pages residing on the same node,
     * in order to prevent random node placement.
     */
    
    #include <linux/kernel.h>
    #include <linux/slab.h>
    
    #include <linux/mm.h>
    #include <linux/swap.h> /* struct reclaim_state */
    #include <linux/cache.h>
    #include <linux/init.h>
    #include <linux/export.h>
    #include <linux/rcupdate.h>
    #include <linux/list.h>
    #include <linux/kmemleak.h>
    
    #include <trace/events/kmem.h>
    
    #include <linux/atomic.h>
    
    #include "slab.h"
    /*
     * slob_block has a field 'units', which indicates size of block if +ve,
     * or offset of next block if -ve (in SLOB_UNITs).
     *
     * Free blocks of size 1 unit simply contain the offset of the next block.
     * Those with larger size contain their size in the first SLOB_UNIT of
     * memory, and the offset of the next free block in the second SLOB_UNIT.
     */
    #if PAGE_SIZE <= (32767 * 2)
    typedef s16 slobidx_t;
    #else
    typedef s32 slobidx_t;
    #endif
    
    struct slob_block {
            slobidx_t units;
    };
    typedef struct slob_block slob_t;
    
    /*
     * All partially free slob pages go on these lists.
     */
    #define SLOB_BREAK1 256
    #define SLOB_BREAK2 1024
   static LIST_HEAD(free_slob_small);
   static LIST_HEAD(free_slob_medium);
   static LIST_HEAD(free_slob_large);
   
   /*
    * slob_page_free: true for pages on free_slob_pages list.
    */
   static inline int slob_page_free(struct page *sp)
   {
           return PageSlobFree(sp);
   }
   
   static void set_slob_page_free(struct page *sp, struct list_head *list)
   {
           list_add(&sp->list, list);
           __SetPageSlobFree(sp);
   }
   
   static inline void clear_slob_page_free(struct page *sp)
   {
           list_del(&sp->list);
           __ClearPageSlobFree(sp);
   }
   
   #define SLOB_UNIT sizeof(slob_t)
   #define SLOB_UNITS(size) (((size) + SLOB_UNIT - 1)/SLOB_UNIT)
   
   /*
    * struct slob_rcu is inserted at the tail of allocated slob blocks, which
    * were created with a SLAB_DESTROY_BY_RCU slab. slob_rcu is used to free
    * the block using call_rcu.
    */
   struct slob_rcu {
           struct rcu_head head;
           int size;
   };
   
   /*
    * slob_lock protects all slob allocator structures.
    */
   static DEFINE_SPINLOCK(slob_lock);
   
   /*
    * Encode the given size and next info into a free slob block s.
    */
   static void set_slob(slob_t *s, slobidx_t size, slob_t *next)
   {
           slob_t *base = (slob_t *)((unsigned long)s & PAGE_MASK);
           slobidx_t offset = next - base;
   
           if (size > 1) {
                   s[0].units = size;
                   s[1].units = offset;
           } else
                   s[0].units = -offset;
   }
   
   /*
    * Return the size of a slob block.
    */
   static slobidx_t slob_units(slob_t *s)
   {
           if (s->units > 0)
                   return s->units;
           return 1;
   }
   
   /*
    * Return the next free slob block pointer after this one.
    */
   static slob_t *slob_next(slob_t *s)
   {
           slob_t *base = (slob_t *)((unsigned long)s & PAGE_MASK);
           slobidx_t next;
   
           if (s[0].units < 0)
                   next = -s[0].units;
           else
                   next = s[1].units;
           return base+next;
   }
   
   /*
    * Returns true if s is the last free block in its page.
    */
   static int slob_last(slob_t *s)
   {
           return !((unsigned long)slob_next(s) & ~PAGE_MASK);
   }
   
   static void *slob_new_pages(gfp_t gfp, int order, int node)
   {
           void *page;
   
   #ifdef CONFIG_NUMA
           if (node != NUMA_NO_NODE)
                   page = alloc_pages_exact_node(node, gfp, order);
           else
   #endif
                   page = alloc_pages(gfp, order);
   
           if (!page)
                   return NULL;
   
           return page_address(page);
   }
   
   static void slob_free_pages(void *b, int order)
   {
           if (current->reclaim_state)
                   current->reclaim_state->reclaimed_slab += 1 << order;
           free_pages((unsigned long)b, order);
   }
   
   /*
    * Allocate a slob block within a given slob_page sp.
    */
   static void *slob_page_alloc(struct page *sp, size_t size, int align)
   {
           slob_t *prev, *cur, *aligned = NULL;
           int delta = 0, units = SLOB_UNITS(size);
   
           for (prev = NULL, cur = sp->freelist; ; prev = cur, cur = slob_next(cur)) {
                   slobidx_t avail = slob_units(cur);
   
                   if (align) {
                           aligned = (slob_t *)ALIGN((unsigned long)cur, align);
                           delta = aligned - cur;
                   }
                   if (avail >= units + delta) { /* room enough? */
                           slob_t *next;
   
                           if (delta) { /* need to fragment head to align? */
                                   next = slob_next(cur);
                                   set_slob(aligned, avail - delta, next);
                                   set_slob(cur, delta, aligned);
                                   prev = cur;
                                   cur = aligned;
                                   avail = slob_units(cur);
                           }
   
                           next = slob_next(cur);
                           if (avail == units) { /* exact fit? unlink. */
                                   if (prev)
                                           set_slob(prev, slob_units(prev), next);
                                   else
                                           sp->freelist = next;
                           } else { /* fragment */
                                   if (prev)
                                           set_slob(prev, slob_units(prev), cur + units);
                                   else
                                           sp->freelist = cur + units;
                                   set_slob(cur + units, avail - units, next);
                           }
   
                           sp->units -= units;
                           if (!sp->units)
                                   clear_slob_page_free(sp);
                           return cur;
                   }
                   if (slob_last(cur))
                           return NULL;
           }
   }
   
   /*
    * slob_alloc: entry point into the slob allocator.
    */
   static void *slob_alloc(size_t size, gfp_t gfp, int align, int node)
   {
           struct page *sp;
           struct list_head *prev;
           struct list_head *slob_list;
           slob_t *b = NULL;
           unsigned long flags;
   
           if (size < SLOB_BREAK1)
                   slob_list = &free_slob_small;
           else if (size < SLOB_BREAK2)
                   slob_list = &free_slob_medium;
           else
                   slob_list = &free_slob_large;
   
           spin_lock_irqsave(&slob_lock, flags);
           /* Iterate through each partially free page, try to find room */
           list_for_each_entry(sp, slob_list, list) {
   #ifdef CONFIG_NUMA
                   /*
                    * If there's a node specification, search for a partial
                    * page with a matching node id in the freelist.
                    */
                   if (node != NUMA_NO_NODE && page_to_nid(sp) != node)
                           continue;
   #endif
                   /* Enough room on this page? */
                   if (sp->units < SLOB_UNITS(size))
                           continue;
   
                   /* Attempt to alloc */
                   prev = sp->list.prev;
                   b = slob_page_alloc(sp, size, align);
                   if (!b)
                           continue;
   
                   /* Improve fragment distribution and reduce our average
                    * search time by starting our next search here. (see
                    * Knuth vol 1, sec 2.5, pg 449) */
                   if (prev != slob_list->prev &&
                                   slob_list->next != prev->next)
                           list_move_tail(slob_list, prev->next);
                   break;
           }
           spin_unlock_irqrestore(&slob_lock, flags);
   
           /* Not enough space: must allocate a new page */
           if (!b) {
                   b = slob_new_pages(gfp & ~__GFP_ZERO, 0, node);
                   if (!b)
                           return NULL;
                   sp = virt_to_page(b);
                   __SetPageSlab(sp);
   
                   spin_lock_irqsave(&slob_lock, flags);
                   sp->units = SLOB_UNITS(PAGE_SIZE);
                   sp->freelist = b;
                   INIT_LIST_HEAD(&sp->list);
                   set_slob(b, SLOB_UNITS(PAGE_SIZE), b + SLOB_UNITS(PAGE_SIZE));
                   set_slob_page_free(sp, slob_list);
                   b = slob_page_alloc(sp, size, align);
                   BUG_ON(!b);
                   spin_unlock_irqrestore(&slob_lock, flags);
           }
           if (unlikely((gfp & __GFP_ZERO) && b))
                   memset(b, 0, size);
           return b;
   }
   
   /*
    * slob_free: entry point into the slob allocator.
    */
   static void slob_free(void *block, int size)
   {
           struct page *sp;
           slob_t *prev, *next, *b = (slob_t *)block;
           slobidx_t units;
           unsigned long flags;
           struct list_head *slob_list;
   
           if (unlikely(ZERO_OR_NULL_PTR(block)))
                   return;
           BUG_ON(!size);
   
           sp = virt_to_page(block);
           units = SLOB_UNITS(size);
   
           spin_lock_irqsave(&slob_lock, flags);
   
           if (sp->units + units == SLOB_UNITS(PAGE_SIZE)) {
                   /* Go directly to page allocator. Do not pass slob allocator */
                   if (slob_page_free(sp))
                           clear_slob_page_free(sp);
                   spin_unlock_irqrestore(&slob_lock, flags);
                   __ClearPageSlab(sp);
                   reset_page_mapcount(sp);
                   slob_free_pages(b, 0);
                   return;
           }
   
           if (!slob_page_free(sp)) {
                   /* This slob page is about to become partially free. Easy! */
                   sp->units = units;
                   sp->freelist = b;
                   set_slob(b, units,
                           (void *)((unsigned long)(b +
                                           SLOB_UNITS(PAGE_SIZE)) & PAGE_MASK));
                   if (size < SLOB_BREAK1)
                           slob_list = &free_slob_small;
                   else if (size < SLOB_BREAK2)
                           slob_list = &free_slob_medium;
                   else
                           slob_list = &free_slob_large;
                   set_slob_page_free(sp, slob_list);
                   goto out;
           }
   
           /*
            * Otherwise the page is already partially free, so find reinsertion
            * point.
            */
           sp->units += units;
   
           if (b < (slob_t *)sp->freelist) {
                   if (b + units == sp->freelist) {
                           units += slob_units(sp->freelist);
                           sp->freelist = slob_next(sp->freelist);
                   }
                   set_slob(b, units, sp->freelist);
                   sp->freelist = b;
           } else {
                   prev = sp->freelist;
                   next = slob_next(prev);
                   while (b > next) {
                           prev = next;
                           next = slob_next(prev);
                   }
   
                   if (!slob_last(prev) && b + units == next) {
                           units += slob_units(next);
                           set_slob(b, units, slob_next(next));
                   } else
                           set_slob(b, units, next);
   
                   if (prev + slob_units(prev) == b) {
                           units = slob_units(b) + slob_units(prev);
                           set_slob(prev, units, slob_next(b));
                   } else
                           set_slob(prev, slob_units(prev), b);
           }
   out:
           spin_unlock_irqrestore(&slob_lock, flags);
   }
   
   /*
    * End of slob allocator proper. Begin kmem_cache_alloc and kmalloc frontend.
    */
   
   static __always_inline void *
   __do_kmalloc_node(size_t size, gfp_t gfp, int node, unsigned long caller)
   {
           unsigned int *m;
           int align = max_t(size_t, ARCH_KMALLOC_MINALIGN, ARCH_SLAB_MINALIGN);
           void *ret;
   
           gfp &= gfp_allowed_mask;
   
           lockdep_trace_alloc(gfp);
   
           if (size < PAGE_SIZE - align) {
                   if (!size)
                           return ZERO_SIZE_PTR;
   
                   m = slob_alloc(size + align, gfp, align, node);
   
                   if (!m)
                           return NULL;
                   *m = size;
                   ret = (void *)m + align;
   
                   trace_kmalloc_node(caller, ret,
                                      size, size + align, gfp, node);
           } else {
                   unsigned int order = get_order(size);
   
                   if (likely(order))
                           gfp |= __GFP_COMP;
                   ret = slob_new_pages(gfp, order, node);
   
                   trace_kmalloc_node(caller, ret,
                                      size, PAGE_SIZE << order, gfp, node);
           }
   
           kmemleak_alloc(ret, size, 1, gfp);
           return ret;
   }
   
   void *__kmalloc_node(size_t size, gfp_t gfp, int node)
   {
           return __do_kmalloc_node(size, gfp, node, _RET_IP_);
   }
   EXPORT_SYMBOL(__kmalloc_node);
   
   #ifdef CONFIG_TRACING
   void *__kmalloc_track_caller(size_t size, gfp_t gfp, unsigned long caller)
   {
           return __do_kmalloc_node(size, gfp, NUMA_NO_NODE, caller);
   }
   
   #ifdef CONFIG_NUMA
   void *__kmalloc_node_track_caller(size_t size, gfp_t gfp,
                                           int node, unsigned long caller)
   {
           return __do_kmalloc_node(size, gfp, node, caller);
   }
   #endif
   #endif
   
   void kfree(const void *block)
   {
           struct page *sp;
   
           trace_kfree(_RET_IP_, block);
   
           if (unlikely(ZERO_OR_NULL_PTR(block)))
                   return;
           kmemleak_free(block);
   
           sp = virt_to_page(block);
           if (PageSlab(sp)) {
                   int align = max_t(size_t, ARCH_KMALLOC_MINALIGN, ARCH_SLAB_MINALIGN);
                   unsigned int *m = (unsigned int *)(block - align);
                   slob_free(m, *m + align);
           } else
                   __free_pages(sp, compound_order(sp));
   }
   EXPORT_SYMBOL(kfree);
   
   /* can't use ksize for kmem_cache_alloc memory, only kmalloc */
   size_t ksize(const void *block)
   {
           struct page *sp;
           int align;
           unsigned int *m;
   
           BUG_ON(!block);
           if (unlikely(block == ZERO_SIZE_PTR))
                   return 0;
   
           sp = virt_to_page(block);
           if (unlikely(!PageSlab(sp)))
                   return PAGE_SIZE << compound_order(sp);
   
           align = max_t(size_t, ARCH_KMALLOC_MINALIGN, ARCH_SLAB_MINALIGN);
           m = (unsigned int *)(block - align);
           return SLOB_UNITS(*m) * SLOB_UNIT;
   }
   EXPORT_SYMBOL(ksize);
   
   int __kmem_cache_create(struct kmem_cache *c, unsigned long flags)
   {
           if (flags & SLAB_DESTROY_BY_RCU) {
                   /* leave room for rcu footer at the end of object */
                   c->size += sizeof(struct slob_rcu);
           }
           c->flags = flags;
           return 0;
   }
   
   void *kmem_cache_alloc_node(struct kmem_cache *c, gfp_t flags, int node)
   {
           void *b;
   
           flags &= gfp_allowed_mask;
   
           lockdep_trace_alloc(flags);
   
           if (c->size < PAGE_SIZE) {
                   b = slob_alloc(c->size, flags, c->align, node);
                   trace_kmem_cache_alloc_node(_RET_IP_, b, c->object_size,
                                               SLOB_UNITS(c->size) * SLOB_UNIT,
                                               flags, node);
           } else {
                   b = slob_new_pages(flags, get_order(c->size), node);
                   trace_kmem_cache_alloc_node(_RET_IP_, b, c->object_size,
                                               PAGE_SIZE << get_order(c->size),
                                               flags, node);
           }
   
           if (c->ctor)
                   c->ctor(b);
   
           kmemleak_alloc_recursive(b, c->size, 1, c->flags, flags);
           return b;
   }
   EXPORT_SYMBOL(kmem_cache_alloc_node);
   
   static void __kmem_cache_free(void *b, int size)
   {
           if (size < PAGE_SIZE)
                   slob_free(b, size);
           else
                   slob_free_pages(b, get_order(size));
   }
   
   static void kmem_rcu_free(struct rcu_head *head)
   {
           struct slob_rcu *slob_rcu = (struct slob_rcu *)head;
           void *b = (void *)slob_rcu - (slob_rcu->size - sizeof(struct slob_rcu));
   
           __kmem_cache_free(b, slob_rcu->size);
   }
   
   void kmem_cache_free(struct kmem_cache *c, void *b)
   {
           kmemleak_free_recursive(b, c->flags);
           if (unlikely(c->flags & SLAB_DESTROY_BY_RCU)) {
                   struct slob_rcu *slob_rcu;
                   slob_rcu = b + (c->size - sizeof(struct slob_rcu));
                   slob_rcu->size = c->size;
                   call_rcu(&slob_rcu->head, kmem_rcu_free);
           } else {
                   __kmem_cache_free(b, c->size);
           }
   
           trace_kmem_cache_free(_RET_IP_, b);
   }
   EXPORT_SYMBOL(kmem_cache_free);
   
   int __kmem_cache_shutdown(struct kmem_cache *c)
   {
           /* No way to check for remaining objects */
           return 0;
   }
   
   int kmem_cache_shrink(struct kmem_cache *d)
   {
           return 0;
   }
   EXPORT_SYMBOL(kmem_cache_shrink);
   
   struct kmem_cache kmem_cache_boot = {
           .name = "kmem_cache",
           .size = sizeof(struct kmem_cache),
           .flags = SLAB_PANIC,
           .align = ARCH_KMALLOC_MINALIGN,
   };
   
   void __init kmem_cache_init(void)
   {
           kmem_cache = &kmem_cache_boot;
           slab_state = UP;
   }
   
   void __init kmem_cache_init_late(void)
   {
           slab_state = FULL;
   }

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