mm/mempool.c

   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/module.h>
  14 #include <linux/mempool.h>
  15 #include <linux/blkdev.h>
  16 #include <linux/writeback.h>
  17
  18 static 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
  24 static void *remove_element(mempool_t *pool)
  25 {
  26         BUG_ON(pool->curr_nr <= 0);
  27         return pool->elements[--pool->curr_nr];
  28 }
  29
  30 static void free_pool(mempool_t *pool)
  31 {
  32         while (pool->curr_nr) {
  33                 void *element = remove_element(pool);
  34                 pool->free(element, pool->pool_data);
  35         }
  36         kfree(pool->elements);
  37         kfree(pool);
  38 }
  39
  40 /**
  41  * mempool_create - create a memory pool
  42  * @min_nr:    the minimum number of elements guaranteed to be
  43  *             allocated for this pool.
  44  * @alloc_fn:  user-defined element-allocation function.
  45  * @free_fn:   user-defined element-freeing function.
  46  * @pool_data: optional private data available to the user-defined functions.
  47  *
  48  * this function creates and allocates a guaranteed size, preallocated
  49  * memory pool. The pool can be used from the mempool_alloc and mempool_free
  50  * functions. This function might sleep. Both the alloc_fn() and the free_fn()
  51  * functions might sleep - as long as the mempool_alloc function is not called
  52  * from IRQ contexts.
  53  */
  54 mempool_t * mempool_create(int min_nr, mempool_alloc_t *alloc_fn,
  55                                 mempool_free_t *free_fn, void *pool_data)
  56 {
  57         mempool_t *pool;
  58
  59         pool = kmalloc(sizeof(*pool), GFP_KERNEL);
  60         if (!pool)
  61                 return NULL;
  62         memset(pool, 0, sizeof(*pool));
  63         pool->elements = kmalloc(min_nr * sizeof(void *), GFP_KERNEL);
  64         if (!pool->elements) {
  65                 kfree(pool);
  66                 return NULL;
  67         }
  68         spin_lock_init(&pool->lock);
  69         pool->min_nr = min_nr;
  70         pool->pool_data = pool_data;
  71         init_waitqueue_head(&pool->wait);
  72         pool->alloc = alloc_fn;
  73         pool->free = free_fn;
  74
  75         /*
  76          * First pre-allocate the guaranteed number of buffers.
  77          */
  78         while (pool->curr_nr < pool->min_nr) {
  79                 void *element;
  80
  81                 element = pool->alloc(GFP_KERNEL, pool->pool_data);
  82                 if (unlikely(!element)) {
  83                         free_pool(pool);
  84                         return NULL;
  85                 }
  86                 add_element(pool, element);
  87         }
  88         return pool;
  89 }
  90 EXPORT_SYMBOL(mempool_create);
  91
  92 /*
  93  * mempool_resize is disabled for now, because it has no callers.  Feel free
  94  * to turn it back on if needed.
  95  */
  96 #if 0
  97 /**
  98  * mempool_resize - resize an existing memory pool
  99  * @pool:       pointer to the memory pool which was allocated via
 100  *              mempool_create().
 101  * @new_min_nr: the new minimum number of elements guaranteed to be
 102  *              allocated for this pool.
 103  * @gfp_mask:   the usual allocation bitmask.
 104  *
 105  * This function shrinks/grows the pool. In the case of growing,
 106  * it cannot be guaranteed that the pool will be grown to the new
 107  * size immediately, but new mempool_free() calls will refill it.
 108  *
 109  * Note, the caller must guarantee that no mempool_destroy is called
 110  * while this function is running. mempool_alloc() & mempool_free()
 111  * might be called (eg. from IRQ contexts) while this function executes.
 112  */
 113 int mempool_resize(mempool_t *pool, int new_min_nr, int gfp_mask)
 114 {
 115         void *element;
 116         void **new_elements;
 117         unsigned long flags;
 118
 119         BUG_ON(new_min_nr <= 0);
 120
 121         spin_lock_irqsave(&pool->lock, flags);
 122         if (new_min_nr < pool->min_nr) {
 123                 while (pool->curr_nr > new_min_nr) {
 124                         element = remove_element(pool);
 125                         spin_unlock_irqrestore(&pool->lock, flags);
 126                         pool->free(element, pool->pool_data);
 127                         spin_lock_irqsave(&pool->lock, flags);
 128                 }
 129                 pool->min_nr = new_min_nr;
 130                 goto out_unlock;
 131         }
 132         spin_unlock_irqrestore(&pool->lock, flags);
 133
 134         /* Grow the pool */
 135         new_elements = kmalloc(new_min_nr * sizeof(*new_elements), gfp_mask);
 136         if (!new_elements)
 137                 return -ENOMEM;
 138
 139         spin_lock_irqsave(&pool->lock, flags);
 140         memcpy(new_elements, pool->elements,
 141                         pool->curr_nr * sizeof(*new_elements));
 142         kfree(pool->elements);
 143         pool->elements = new_elements;
 144         pool->min_nr = new_min_nr;
 145
 146         while (pool->curr_nr < pool->min_nr) {
 147                 spin_unlock_irqrestore(&pool->lock, flags);
 148                 element = pool->alloc(gfp_mask, pool->pool_data);
 149                 if (!element)
 150                         goto out;
 151                 spin_lock_irqsave(&pool->lock, flags);
 152                 if (pool->curr_nr < pool->min_nr) {
 153                         add_element(pool, element);
 154                 } else {
 155                         spin_unlock_irqrestore(&pool->lock, flags);
 156                         pool->free(element, pool->pool_data);   /* Raced */
 157                         spin_lock_irqsave(&pool->lock, flags);
 158                 }
 159         }
 160 out_unlock:
 161         spin_unlock_irqrestore(&pool->lock, flags);
 162 out:
 163         return 0;
 164 }
 165 EXPORT_SYMBOL(mempool_resize);
 166 #endif
 167
 168 /**
 169  * mempool_destroy - deallocate a memory pool
 170  * @pool:      pointer to the memory pool which was allocated via
 171  *             mempool_create().
 172  *
 173  * this function only sleeps if the free_fn() function sleeps. The caller
 174  * has to guarantee that all elements have been returned to the pool (ie:
 175  * freed) prior to calling mempool_destroy().
 176  */
 177 void mempool_destroy(mempool_t *pool)
 178 {
 179         if (pool->curr_nr != pool->min_nr)
 180                 BUG();          /* There were outstanding elements */
 181         free_pool(pool);
 182 }
 183 EXPORT_SYMBOL(mempool_destroy);
 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  */
 196 void * mempool_alloc(mempool_t *pool, int gfp_mask)
 197 {
 198         void *element;
 199         unsigned long flags;
 200         DEFINE_WAIT(wait);
 201         int gfp_nowait = gfp_mask & ~(__GFP_WAIT | __GFP_IO);
 202
 203 repeat_alloc:
 204         element = pool->alloc(gfp_nowait|__GFP_NOWARN, pool->pool_data);
 205         if (likely(element != NULL))
 206                 return element;
 207
 208         /*
 209          * If the pool is less than 50% full and we can perform effective
 210          * page reclaim then try harder to allocate an element.
 211          */
 212         if ((gfp_mask & __GFP_FS) && (gfp_mask != gfp_nowait) &&
 213                                 (pool->curr_nr <= pool->min_nr/2)) {
 214                 element = pool->alloc(gfp_mask, pool->pool_data);
 215                 if (likely(element != NULL))
 216                         return element;
 217         }
 218
 219         /*
 220          * Kick the VM at this point.
 221          */
 222         wakeup_bdflush(0);
 223
 224         spin_lock_irqsave(&pool->lock, flags);
 225         if (likely(pool->curr_nr)) {
 226                 element = remove_element(pool);
 227                 spin_unlock_irqrestore(&pool->lock, flags);
 228                 return element;
 229         }
 230         spin_unlock_irqrestore(&pool->lock, flags);
 231
 232         /* We must not sleep in the GFP_ATOMIC case */
 233         if (!(gfp_mask & __GFP_WAIT))
 234                 return NULL;
 235
 236         blk_run_queues();
 237
 238         prepare_to_wait(&pool->wait, &wait, TASK_UNINTERRUPTIBLE);
 239         if (!pool->curr_nr)
 240                 io_schedule();
 241         finish_wait(&pool->wait, &wait);
 242
 243         goto repeat_alloc;
 244 }
 245 EXPORT_SYMBOL(mempool_alloc);
 246
 247 /**
 248  * mempool_free - return an element to the pool.
 249  * @element:   pool element pointer.
 250  * @pool:      pointer to the memory pool which was allocated via
 251  *             mempool_create().
 252  *
 253  * this function only sleeps if the free_fn() function sleeps.
 254  */
 255 void mempool_free(void *element, mempool_t *pool)
 256 {
 257         unsigned long flags;
 258
 259         if (pool->curr_nr < pool->min_nr) {
 260                 spin_lock_irqsave(&pool->lock, flags);
 261                 if (pool->curr_nr < pool->min_nr) {
 262                         add_element(pool, element);
 263                         spin_unlock_irqrestore(&pool->lock, flags);
 264                         wake_up(&pool->wait);
 265                         return;
 266                 }
 267                 spin_unlock_irqrestore(&pool->lock, flags);
 268         }
 269         pool->free(element, pool->pool_data);
 270 }
 271 EXPORT_SYMBOL(mempool_free);
 272
 273 /*
 274  * A commonly used alloc and free fn.
 275  */
 276 void *mempool_alloc_slab(int gfp_mask, void *pool_data)
 277 {
 278         kmem_cache_t *mem = (kmem_cache_t *) pool_data;
 279         return kmem_cache_alloc(mem, gfp_mask);
 280 }
 281 EXPORT_SYMBOL(mempool_alloc_slab);
 282
 283 void mempool_free_slab(void *element, void *pool_data)
 284 {
 285         kmem_cache_t *mem = (kmem_cache_t *) pool_data;
 286         kmem_cache_free(mem, element);
 287 }
 288 EXPORT_SYMBOL(mempool_free_slab);