linux/mm/mempool.c
<<
>>
Prefs
   1/*
   2 *  linux/mm/mempool.c
   3 *
   4 *  memory buffer pool support. Such pools are mostly used
   5 *  for guaranteed, deadlock-free memory allocations during
   6 *  extreme VM load.
   7 *
   8 *  started by Ingo Molnar, Copyright (C) 2001
   9 */
  10
  11#include <linux/mm.h>
  12#include <linux/slab.h>
  13#include <linux/export.h>
  14#include <linux/mempool.h>
  15#include <linux/blkdev.h>
  16#include <linux/writeback.h>
  17
  18static void add_element(mempool_t *pool, void *element)
  19{
  20        BUG_ON(pool->curr_nr >= pool->min_nr);
  21        pool->elements[pool->curr_nr++] = element;
  22}
  23
  24static void *remove_element(mempool_t *pool)
  25{
  26        BUG_ON(pool->curr_nr <= 0);
  27        return pool->elements[--pool->curr_nr];
  28}
  29
  30/**
  31 * mempool_destroy - deallocate a memory pool
  32 * @pool:      pointer to the memory pool which was allocated via
  33 *             mempool_create().
  34 *
  35 * Free all reserved elements in @pool and @pool itself.  This function
  36 * only sleeps if the free_fn() function sleeps.
  37 */
  38void mempool_destroy(mempool_t *pool)
  39{
  40        while (pool->curr_nr) {
  41                void *element = remove_element(pool);
  42                pool->free(element, pool->pool_data);
  43        }
  44        kfree(pool->elements);
  45        kfree(pool);
  46}
  47EXPORT_SYMBOL(mempool_destroy);
  48
  49/**
  50 * mempool_create - create a memory pool
  51 * @min_nr:    the minimum number of elements guaranteed to be
  52 *             allocated for this pool.
  53 * @alloc_fn:  user-defined element-allocation function.
  54 * @free_fn:   user-defined element-freeing function.
  55 * @pool_data: optional private data available to the user-defined functions.
  56 *
  57 * this function creates and allocates a guaranteed size, preallocated
  58 * memory pool. The pool can be used from the mempool_alloc() and mempool_free()
  59 * functions. This function might sleep. Both the alloc_fn() and the free_fn()
  60 * functions might sleep - as long as the mempool_alloc() function is not called
  61 * from IRQ contexts.
  62 */
  63mempool_t *mempool_create(int min_nr, mempool_alloc_t *alloc_fn,
  64                                mempool_free_t *free_fn, void *pool_data)
  65{
  66        return mempool_create_node(min_nr,alloc_fn,free_fn, pool_data,
  67                                   GFP_KERNEL, NUMA_NO_NODE);
  68}
  69EXPORT_SYMBOL(mempool_create);
  70
  71mempool_t *mempool_create_node(int min_nr, mempool_alloc_t *alloc_fn,
  72                               mempool_free_t *free_fn, void *pool_data,
  73                               gfp_t gfp_mask, int node_id)
  74{
  75        mempool_t *pool;
  76        pool = kzalloc_node(sizeof(*pool), gfp_mask, node_id);
  77        if (!pool)
  78                return NULL;
  79        pool->elements = kmalloc_node(min_nr * sizeof(void *),
  80                                      gfp_mask, node_id);
  81        if (!pool->elements) {
  82                kfree(pool);
  83                return NULL;
  84        }
  85        spin_lock_init(&pool->lock);
  86        pool->min_nr = min_nr;
  87        pool->pool_data = pool_data;
  88        init_waitqueue_head(&pool->wait);
  89        pool->alloc = alloc_fn;
  90        pool->free = free_fn;
  91
  92        /*
  93         * First pre-allocate the guaranteed number of buffers.
  94         */
  95        while (pool->curr_nr < pool->min_nr) {
  96                void *element;
  97
  98                element = pool->alloc(gfp_mask, pool->pool_data);
  99                if (unlikely(!element)) {
 100                        mempool_destroy(pool);
 101                        return NULL;
 102                }
 103                add_element(pool, element);
 104        }
 105        return pool;
 106}
 107EXPORT_SYMBOL(mempool_create_node);
 108
 109/**
 110 * mempool_resize - resize an existing memory pool
 111 * @pool:       pointer to the memory pool which was allocated via
 112 *              mempool_create().
 113 * @new_min_nr: the new minimum number of elements guaranteed to be
 114 *              allocated for this pool.
 115 * @gfp_mask:   the usual allocation bitmask.
 116 *
 117 * This function shrinks/grows the pool. In the case of growing,
 118 * it cannot be guaranteed that the pool will be grown to the new
 119 * size immediately, but new mempool_free() calls will refill it.
 120 *
 121 * Note, the caller must guarantee that no mempool_destroy is called
 122 * while this function is running. mempool_alloc() & mempool_free()
 123 * might be called (eg. from IRQ contexts) while this function executes.
 124 */
 125int mempool_resize(mempool_t *pool, int new_min_nr, gfp_t gfp_mask)
 126{
 127        void *element;
 128        void **new_elements;
 129        unsigned long flags;
 130
 131        BUG_ON(new_min_nr <= 0);
 132
 133        spin_lock_irqsave(&pool->lock, flags);
 134        if (new_min_nr <= pool->min_nr) {
 135                while (new_min_nr < pool->curr_nr) {
 136                        element = remove_element(pool);
 137                        spin_unlock_irqrestore(&pool->lock, flags);
 138                        pool->free(element, pool->pool_data);
 139                        spin_lock_irqsave(&pool->lock, flags);
 140                }
 141                pool->min_nr = new_min_nr;
 142                goto out_unlock;
 143        }
 144        spin_unlock_irqrestore(&pool->lock, flags);
 145
 146        /* Grow the pool */
 147        new_elements = kmalloc(new_min_nr * sizeof(*new_elements), gfp_mask);
 148        if (!new_elements)
 149                return -ENOMEM;
 150
 151        spin_lock_irqsave(&pool->lock, flags);
 152        if (unlikely(new_min_nr <= pool->min_nr)) {
 153                /* Raced, other resize will do our work */
 154                spin_unlock_irqrestore(&pool->lock, flags);
 155                kfree(new_elements);
 156                goto out;
 157        }
 158        memcpy(new_elements, pool->elements,
 159                        pool->curr_nr * sizeof(*new_elements));
 160        kfree(pool->elements);
 161        pool->elements = new_elements;
 162        pool->min_nr = new_min_nr;
 163
 164        while (pool->curr_nr < pool->min_nr) {
 165                spin_unlock_irqrestore(&pool->lock, flags);
 166                element = pool->alloc(gfp_mask, pool->pool_data);
 167                if (!element)
 168                        goto out;
 169                spin_lock_irqsave(&pool->lock, flags);
 170                if (pool->curr_nr < pool->min_nr) {
 171                        add_element(pool, element);
 172                } else {
 173                        spin_unlock_irqrestore(&pool->lock, flags);
 174                        pool->free(element, pool->pool_data);   /* Raced */
 175                        goto out;
 176                }
 177        }
 178out_unlock:
 179        spin_unlock_irqrestore(&pool->lock, flags);
 180out:
 181        return 0;
 182}
 183EXPORT_SYMBOL(mempool_resize);
 184
 185/**
 186 * mempool_alloc - allocate an element from a specific memory pool
 187 * @pool:      pointer to the memory pool which was allocated via
 188 *             mempool_create().
 189 * @gfp_mask:  the usual allocation bitmask.
 190 *
 191 * this function only sleeps if the alloc_fn() function sleeps or
 192 * returns NULL. Note that due to preallocation, this function
 193 * *never* fails when called from process contexts. (it might
 194 * fail if called from an IRQ context.)
 195 */
 196void * mempool_alloc(mempool_t *pool, gfp_t gfp_mask)
 197{
 198        void *element;
 199        unsigned long flags;
 200        wait_queue_t wait;
 201        gfp_t gfp_temp;
 202
 203        might_sleep_if(gfp_mask & __GFP_WAIT);
 204
 205        gfp_mask |= __GFP_NOMEMALLOC;   /* don't allocate emergency reserves */
 206        gfp_mask |= __GFP_NORETRY;      /* don't loop in __alloc_pages */
 207        gfp_mask |= __GFP_NOWARN;       /* failures are OK */
 208
 209        gfp_temp = gfp_mask & ~(__GFP_WAIT|__GFP_IO);
 210
 211repeat_alloc:
 212
 213        element = pool->alloc(gfp_temp, pool->pool_data);
 214        if (likely(element != NULL))
 215                return element;
 216
 217        spin_lock_irqsave(&pool->lock, flags);
 218        if (likely(pool->curr_nr)) {
 219                element = remove_element(pool);
 220                spin_unlock_irqrestore(&pool->lock, flags);
 221                /* paired with rmb in mempool_free(), read comment there */
 222                smp_wmb();
 223                return element;
 224        }
 225
 226        /*
 227         * We use gfp mask w/o __GFP_WAIT or IO for the first round.  If
 228         * alloc failed with that and @pool was empty, retry immediately.
 229         */
 230        if (gfp_temp != gfp_mask) {
 231                spin_unlock_irqrestore(&pool->lock, flags);
 232                gfp_temp = gfp_mask;
 233                goto repeat_alloc;
 234        }
 235
 236        /* We must not sleep if !__GFP_WAIT */
 237        if (!(gfp_mask & __GFP_WAIT)) {
 238                spin_unlock_irqrestore(&pool->lock, flags);
 239                return NULL;
 240        }
 241
 242        /* Let's wait for someone else to return an element to @pool */
 243        init_wait(&wait);
 244        prepare_to_wait(&pool->wait, &wait, TASK_UNINTERRUPTIBLE);
 245
 246        spin_unlock_irqrestore(&pool->lock, flags);
 247
 248        /*
 249         * FIXME: this should be io_schedule().  The timeout is there as a
 250         * workaround for some DM problems in 2.6.18.
 251         */
 252        io_schedule_timeout(5*HZ);
 253
 254        finish_wait(&pool->wait, &wait);
 255        goto repeat_alloc;
 256}
 257EXPORT_SYMBOL(mempool_alloc);
 258
 259/**
 260 * mempool_free - return an element to the pool.
 261 * @element:   pool element pointer.
 262 * @pool:      pointer to the memory pool which was allocated via
 263 *             mempool_create().
 264 *
 265 * this function only sleeps if the free_fn() function sleeps.
 266 */
 267void mempool_free(void *element, mempool_t *pool)
 268{
 269        unsigned long flags;
 270
 271        if (unlikely(element == NULL))
 272                return;
 273
 274        /*
 275         * Paired with the wmb in mempool_alloc().  The preceding read is
 276         * for @element and the following @pool->curr_nr.  This ensures
 277         * that the visible value of @pool->curr_nr is from after the
 278         * allocation of @element.  This is necessary for fringe cases
 279         * where @element was passed to this task without going through
 280         * barriers.
 281         *
 282         * For example, assume @p is %NULL at the beginning and one task
 283         * performs "p = mempool_alloc(...);" while another task is doing
 284         * "while (!p) cpu_relax(); mempool_free(p, ...);".  This function
 285         * may end up using curr_nr value which is from before allocation
 286         * of @p without the following rmb.
 287         */
 288        smp_rmb();
 289
 290        /*
 291         * For correctness, we need a test which is guaranteed to trigger
 292         * if curr_nr + #allocated == min_nr.  Testing curr_nr < min_nr
 293         * without locking achieves that and refilling as soon as possible
 294         * is desirable.
 295         *
 296         * Because curr_nr visible here is always a value after the
 297         * allocation of @element, any task which decremented curr_nr below
 298         * min_nr is guaranteed to see curr_nr < min_nr unless curr_nr gets
 299         * incremented to min_nr afterwards.  If curr_nr gets incremented
 300         * to min_nr after the allocation of @element, the elements
 301         * allocated after that are subject to the same guarantee.
 302         *
 303         * Waiters happen iff curr_nr is 0 and the above guarantee also
 304         * ensures that there will be frees which return elements to the
 305         * pool waking up the waiters.
 306         */
 307        if (pool->curr_nr < pool->min_nr) {
 308                spin_lock_irqsave(&pool->lock, flags);
 309                if (pool->curr_nr < pool->min_nr) {
 310                        add_element(pool, element);
 311                        spin_unlock_irqrestore(&pool->lock, flags);
 312                        wake_up(&pool->wait);
 313                        return;
 314                }
 315                spin_unlock_irqrestore(&pool->lock, flags);
 316        }
 317        pool->free(element, pool->pool_data);
 318}
 319EXPORT_SYMBOL(mempool_free);
 320
 321/*
 322 * A commonly used alloc and free fn.
 323 */
 324void *mempool_alloc_slab(gfp_t gfp_mask, void *pool_data)
 325{
 326        struct kmem_cache *mem = pool_data;
 327        return kmem_cache_alloc(mem, gfp_mask);
 328}
 329EXPORT_SYMBOL(mempool_alloc_slab);
 330
 331void mempool_free_slab(void *element, void *pool_data)
 332{
 333        struct kmem_cache *mem = pool_data;
 334        kmem_cache_free(mem, element);
 335}
 336EXPORT_SYMBOL(mempool_free_slab);
 337
 338/*
 339 * A commonly used alloc and free fn that kmalloc/kfrees the amount of memory
 340 * specified by pool_data
 341 */
 342void *mempool_kmalloc(gfp_t gfp_mask, void *pool_data)
 343{
 344        size_t size = (size_t)pool_data;
 345        return kmalloc(size, gfp_mask);
 346}
 347EXPORT_SYMBOL(mempool_kmalloc);
 348
 349void mempool_kfree(void *element, void *pool_data)
 350{
 351        kfree(element);
 352}
 353EXPORT_SYMBOL(mempool_kfree);
 354
 355/*
 356 * A simple mempool-backed page allocator that allocates pages
 357 * of the order specified by pool_data.
 358 */
 359void *mempool_alloc_pages(gfp_t gfp_mask, void *pool_data)
 360{
 361        int order = (int)(long)pool_data;
 362        return alloc_pages(gfp_mask, order);
 363}
 364EXPORT_SYMBOL(mempool_alloc_pages);
 365
 366void mempool_free_pages(void *element, void *pool_data)
 367{
 368        int order = (int)(long)pool_data;
 369        __free_pages(element, order);
 370}
 371EXPORT_SYMBOL(mempool_free_pages);
 372
lxr.linux.no kindly hosted by Redpill Linpro AS, provider of Linux consulting and operations services since 1995.