/*
 *  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,-1);
}
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, int node_id)
{
        mempool_t *pool;
        pool = kmalloc_node(sizeof(*pool), GFP_KERNEL | __GFP_ZERO, node_id);
        if (!pool)
                return NULL;
        pool->elements = kmalloc_node(min_nr * sizeof(void *),
                                        GFP_KERNEL, 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_KERNEL, 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);