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

     /*
      *  linux/mm/mempool.c
      *
      *  memory buffer pool support. Such pools are mostly used
      *  for guaranteed, deadlock-free memory allocations during
      *  extreme VM load.
      *
      *  started by Ingo Molnar, Copyright (C) 2001
      */
    
    #include <linux/mm.h>
    #include <linux/slab.h>
    #include <linux/export.h>
    #include <linux/mempool.h>
    #include <linux/blkdev.h>
    #include <linux/writeback.h>
    
    static void add_element(mempool_t *pool, void *element)
    {
            BUG_ON(pool->curr_nr >= pool->min_nr);
            pool->elements[pool->curr_nr++] = element;
    }
    
    static void *remove_element(mempool_t *pool)
    {
            BUG_ON(pool->curr_nr <= 0);
            return pool->elements[--pool->curr_nr];
    }
    
    /**
     * mempool_destroy - deallocate a memory pool
     * @pool:      pointer to the memory pool which was allocated via
     *             mempool_create().
     *
     * Free all reserved elements in @pool and @pool itself.  This function
     * only sleeps if the free_fn() function sleeps.
     */
    void mempool_destroy(mempool_t *pool)
    {
            while (pool->curr_nr) {
                    void *element = remove_element(pool);
                    pool->free(element, pool->pool_data);
            }
            kfree(pool->elements);
            kfree(pool);
    }
    EXPORT_SYMBOL(mempool_destroy);
    
    /**
     * mempool_create - create a memory pool
     * @min_nr:    the minimum number of elements guaranteed to be
     *             allocated for this pool.
     * @alloc_fn:  user-defined element-allocation function.
     * @free_fn:   user-defined element-freeing function.
     * @pool_data: optional private data available to the user-defined functions.
     *
     * this function creates and allocates a guaranteed size, preallocated
     * memory pool. The pool can be used from the mempool_alloc() and mempool_free()
     * functions. This function might sleep. Both the alloc_fn() and the free_fn()
     * functions might sleep - as long as the mempool_alloc() function is not called
     * from IRQ contexts.
     */
    mempool_t *mempool_create(int min_nr, mempool_alloc_t *alloc_fn,
                                    mempool_free_t *free_fn, void *pool_data)
    {
            return mempool_create_node(min_nr,alloc_fn,free_fn, pool_data,
                                       GFP_KERNEL, NUMA_NO_NODE);
    }
    EXPORT_SYMBOL(mempool_create);
    
    mempool_t *mempool_create_node(int min_nr, mempool_alloc_t *alloc_fn,
                                   mempool_free_t *free_fn, void *pool_data,
                                   gfp_t gfp_mask, int node_id)
    {
            mempool_t *pool;
            pool = kmalloc_node(sizeof(*pool), gfp_mask | __GFP_ZERO, node_id);
            if (!pool)
                    return NULL;
            pool->elements = kmalloc_node(min_nr * sizeof(void *),
                                          gfp_mask, node_id);
            if (!pool->elements) {
                    kfree(pool);
                    return NULL;
            }
            spin_lock_init(&pool->lock);
            pool->min_nr = min_nr;
            pool->pool_data = pool_data;
            init_waitqueue_head(&pool->wait);
            pool->alloc = alloc_fn;
            pool->free = free_fn;
    
            /*
             * First pre-allocate the guaranteed number of buffers.
             */
            while (pool->curr_nr < pool->min_nr) {
                    void *element;
    
                    element = pool->alloc(gfp_mask, pool->pool_data);
                    if (unlikely(!element)) {
                           mempool_destroy(pool);
                           return NULL;
                   }
                   add_element(pool, element);
           }
           return pool;
   }
   EXPORT_SYMBOL(mempool_create_node);
   
   /**
    * mempool_resize - resize an existing memory pool
    * @pool:       pointer to the memory pool which was allocated via
    *              mempool_create().
    * @new_min_nr: the new minimum number of elements guaranteed to be
    *              allocated for this pool.
    * @gfp_mask:   the usual allocation bitmask.
    *
    * This function shrinks/grows the pool. In the case of growing,
    * it cannot be guaranteed that the pool will be grown to the new
    * size immediately, but new mempool_free() calls will refill it.
    *
    * Note, the caller must guarantee that no mempool_destroy is called
    * while this function is running. mempool_alloc() & mempool_free()
    * might be called (eg. from IRQ contexts) while this function executes.
    */
   int mempool_resize(mempool_t *pool, int new_min_nr, gfp_t gfp_mask)
   {
           void *element;
           void **new_elements;
           unsigned long flags;
   
           BUG_ON(new_min_nr <= 0);
   
           spin_lock_irqsave(&pool->lock, flags);
           if (new_min_nr <= pool->min_nr) {
                   while (new_min_nr < pool->curr_nr) {
                           element = remove_element(pool);
                           spin_unlock_irqrestore(&pool->lock, flags);
                           pool->free(element, pool->pool_data);
                           spin_lock_irqsave(&pool->lock, flags);
                   }
                   pool->min_nr = new_min_nr;
                   goto out_unlock;
           }
           spin_unlock_irqrestore(&pool->lock, flags);
   
           /* Grow the pool */
           new_elements = kmalloc(new_min_nr * sizeof(*new_elements), gfp_mask);
           if (!new_elements)
                   return -ENOMEM;
   
           spin_lock_irqsave(&pool->lock, flags);
           if (unlikely(new_min_nr <= pool->min_nr)) {
                   /* Raced, other resize will do our work */
                   spin_unlock_irqrestore(&pool->lock, flags);
                   kfree(new_elements);
                   goto out;
           }
           memcpy(new_elements, pool->elements,
                           pool->curr_nr * sizeof(*new_elements));
           kfree(pool->elements);
           pool->elements = new_elements;
           pool->min_nr = new_min_nr;
   
           while (pool->curr_nr < pool->min_nr) {
                   spin_unlock_irqrestore(&pool->lock, flags);
                   element = pool->alloc(gfp_mask, pool->pool_data);
                   if (!element)
                           goto out;
                   spin_lock_irqsave(&pool->lock, flags);
                   if (pool->curr_nr < pool->min_nr) {
                           add_element(pool, element);
                   } else {
                           spin_unlock_irqrestore(&pool->lock, flags);
                           pool->free(element, pool->pool_data);   /* Raced */
                           goto out;
                   }
           }
   out_unlock:
           spin_unlock_irqrestore(&pool->lock, flags);
   out:
           return 0;
   }
   EXPORT_SYMBOL(mempool_resize);
   
   /**
    * mempool_alloc - allocate an element from a specific memory pool
    * @pool:      pointer to the memory pool which was allocated via
    *             mempool_create().
    * @gfp_mask:  the usual allocation bitmask.
    *
    * this function only sleeps if the alloc_fn() function sleeps or
    * returns NULL. Note that due to preallocation, this function
    * *never* fails when called from process contexts. (it might
    * fail if called from an IRQ context.)
    */
   void * mempool_alloc(mempool_t *pool, gfp_t gfp_mask)
   {
           void *element;
           unsigned long flags;
           wait_queue_t wait;
           gfp_t gfp_temp;
   
           might_sleep_if(gfp_mask & __GFP_WAIT);
   
           gfp_mask |= __GFP_NOMEMALLOC;   /* don't allocate emergency reserves */
           gfp_mask |= __GFP_NORETRY;      /* don't loop in __alloc_pages */
           gfp_mask |= __GFP_NOWARN;       /* failures are OK */
   
           gfp_temp = gfp_mask & ~(__GFP_WAIT|__GFP_IO);
   
   repeat_alloc:
   
           element = pool->alloc(gfp_temp, pool->pool_data);
           if (likely(element != NULL))
                   return element;
   
           spin_lock_irqsave(&pool->lock, flags);
           if (likely(pool->curr_nr)) {
                   element = remove_element(pool);
                   spin_unlock_irqrestore(&pool->lock, flags);
                   /* paired with rmb in mempool_free(), read comment there */
                   smp_wmb();
                   return element;
           }
   
           /*
            * We use gfp mask w/o __GFP_WAIT or IO for the first round.  If
            * alloc failed with that and @pool was empty, retry immediately.
            */
           if (gfp_temp != gfp_mask) {
                   spin_unlock_irqrestore(&pool->lock, flags);
                   gfp_temp = gfp_mask;
                   goto repeat_alloc;
           }
   
           /* We must not sleep if !__GFP_WAIT */
           if (!(gfp_mask & __GFP_WAIT)) {
                   spin_unlock_irqrestore(&pool->lock, flags);
                   return NULL;
           }
   
           /* Let's wait for someone else to return an element to @pool */
           init_wait(&wait);
           prepare_to_wait(&pool->wait, &wait, TASK_UNINTERRUPTIBLE);
   
           spin_unlock_irqrestore(&pool->lock, flags);
   
           /*
            * FIXME: this should be io_schedule().  The timeout is there as a
            * workaround for some DM problems in 2.6.18.
            */
           io_schedule_timeout(5*HZ);
   
           finish_wait(&pool->wait, &wait);
           goto repeat_alloc;
   }
   EXPORT_SYMBOL(mempool_alloc);
   
   /**
    * mempool_free - return an element to the pool.
    * @element:   pool element pointer.
    * @pool:      pointer to the memory pool which was allocated via
    *             mempool_create().
    *
    * this function only sleeps if the free_fn() function sleeps.
    */
   void mempool_free(void *element, mempool_t *pool)
   {
           unsigned long flags;
   
           if (unlikely(element == NULL))
                   return;
   
           /*
            * Paired with the wmb in mempool_alloc().  The preceding read is
            * for @element and the following @pool->curr_nr.  This ensures
            * that the visible value of @pool->curr_nr is from after the
            * allocation of @element.  This is necessary for fringe cases
            * where @element was passed to this task without going through
            * barriers.
            *
            * For example, assume @p is %NULL at the beginning and one task
            * performs "p = mempool_alloc(...);" while another task is doing
            * "while (!p) cpu_relax(); mempool_free(p, ...);".  This function
            * may end up using curr_nr value which is from before allocation
            * of @p without the following rmb.
            */
           smp_rmb();
   
           /*
            * For correctness, we need a test which is guaranteed to trigger
            * if curr_nr + #allocated == min_nr.  Testing curr_nr < min_nr
            * without locking achieves that and refilling as soon as possible
            * is desirable.
            *
            * Because curr_nr visible here is always a value after the
            * allocation of @element, any task which decremented curr_nr below
            * min_nr is guaranteed to see curr_nr < min_nr unless curr_nr gets
            * incremented to min_nr afterwards.  If curr_nr gets incremented
            * to min_nr after the allocation of @element, the elements
            * allocated after that are subject to the same guarantee.
            *
            * Waiters happen iff curr_nr is 0 and the above guarantee also
            * ensures that there will be frees which return elements to the
            * pool waking up the waiters.
            */
           if (pool->curr_nr < pool->min_nr) {
                   spin_lock_irqsave(&pool->lock, flags);
                   if (pool->curr_nr < pool->min_nr) {
                           add_element(pool, element);
                           spin_unlock_irqrestore(&pool->lock, flags);
                           wake_up(&pool->wait);
                           return;
                   }
                   spin_unlock_irqrestore(&pool->lock, flags);
           }
           pool->free(element, pool->pool_data);
   }
   EXPORT_SYMBOL(mempool_free);
   
   /*
    * A commonly used alloc and free fn.
    */
   void *mempool_alloc_slab(gfp_t gfp_mask, void *pool_data)
   {
           struct kmem_cache *mem = pool_data;
           return kmem_cache_alloc(mem, gfp_mask);
   }
   EXPORT_SYMBOL(mempool_alloc_slab);
   
   void mempool_free_slab(void *element, void *pool_data)
   {
           struct kmem_cache *mem = pool_data;
           kmem_cache_free(mem, element);
   }
   EXPORT_SYMBOL(mempool_free_slab);
   
   /*
    * A commonly used alloc and free fn that kmalloc/kfrees the amount of memory
    * specified by pool_data
    */
   void *mempool_kmalloc(gfp_t gfp_mask, void *pool_data)
   {
           size_t size = (size_t)pool_data;
           return kmalloc(size, gfp_mask);
   }
   EXPORT_SYMBOL(mempool_kmalloc);
   
   void mempool_kfree(void *element, void *pool_data)
   {
           kfree(element);
   }
   EXPORT_SYMBOL(mempool_kfree);
   
   /*
    * A simple mempool-backed page allocator that allocates pages
    * of the order specified by pool_data.
    */
   void *mempool_alloc_pages(gfp_t gfp_mask, void *pool_data)
   {
           int order = (int)(long)pool_data;
           return alloc_pages(gfp_mask, order);
   }
   EXPORT_SYMBOL(mempool_alloc_pages);
   
   void mempool_free_pages(void *element, void *pool_data)
   {
           int order = (int)(long)pool_data;
           __free_pages(element, order);
   }
   EXPORT_SYMBOL(mempool_free_pages);

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