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 - resize an existing memory pool
  94  * @pool:       pointer to the memory pool which was allocated via
  95  *              mempool_create().
  96  * @new_min_nr: the new minimum number of elements guaranteed to be
  97  *              allocated for this pool.
  98  * @gfp_mask:   the usual allocation bitmask.
  99  *
 100  * This function shrinks/grows the pool. In the case of growing,
 101  * it cannot be guaranteed that the pool will be grown to the new
 102  * size immediately, but new mempool_free() calls will refill it.
 103  *
 104  * Note, the caller must guarantee that no mempool_destroy is called
 105  * while this function is running. mempool_alloc() & mempool_free()
 106  * might be called (eg. from IRQ contexts) while this function executes.
 107  */
 108 int mempool_resize(mempool_t *pool, int new_min_nr, int gfp_mask)
 109 {
 110         void *element;
 111         void **new_elements;
 112         unsigned long flags;
 113
 114         BUG_ON(new_min_nr <= 0);
 115
 116         spin_lock_irqsave(&pool->lock, flags);
 117         if (new_min_nr < pool->min_nr) {
 118                 while (pool->curr_nr > new_min_nr) {
 119                         element = remove_element(pool);
 120                         spin_unlock_irqrestore(&pool->lock, flags);
 121                         pool->free(element, pool->pool_data);
 122                         spin_lock_irqsave(&pool->lock, flags);
 123                 }
 124                 pool->min_nr = new_min_nr;
 125                 goto out_unlock;
 126         }
 127         spin_unlock_irqrestore(&pool->lock, flags);
 128
 129         /* Grow the pool */
 130         new_elements = kmalloc(new_min_nr * sizeof(*new_elements), gfp_mask);
 131         if (!new_elements)
 132                 return -ENOMEM;
 133
 134         spin_lock_irqsave(&pool->lock, flags);
 135         memcpy(new_elements, pool->elements,
 136                         pool->curr_nr * sizeof(*new_elements));
 137         kfree(pool->elements);
 138         pool->elements = new_elements;
 139         pool->min_nr = new_min_nr;
 140
 141         while (pool->curr_nr < pool->min_nr) {
 142                 spin_unlock_irqrestore(&pool->lock, flags);
 143                 element = pool->alloc(gfp_mask, pool->pool_data);
 144                 if (!element)
 145                         goto out;
 146                 spin_lock_irqsave(&pool->lock, flags);
 147                 if (pool->curr_nr < pool->min_nr) {
 148                         add_element(pool, element);
 149                 } else {
 150                         spin_unlock_irqrestore(&pool->lock, flags);
 151                         pool->free(element, pool->pool_data);   /* Raced */
 152                         spin_lock_irqsave(&pool->lock, flags);
 153                 }
 154         }
 155 out_unlock:
 156         spin_unlock_irqrestore(&pool->lock, flags);
 157 out:
 158         return 0;
 159 }
 160 EXPORT_SYMBOL(mempool_resize);
 161
 162 /**
 163  * mempool_destroy - deallocate a memory pool
 164  * @pool:      pointer to the memory pool which was allocated via
 165  *             mempool_create().
 166  *
 167  * this function only sleeps if the free_fn() function sleeps. The caller
 168  * has to guarantee that all elements have been returned to the pool (ie:
 169  * freed) prior to calling mempool_destroy().
 170  */
 171 void mempool_destroy(mempool_t *pool)
 172 {
 173         if (pool->curr_nr != pool->min_nr)
 174                 BUG();          /* There were outstanding elements */
 175         free_pool(pool);
 176 }
 177 EXPORT_SYMBOL(mempool_destroy);
 178
 179 /**
 180  * mempool_alloc - allocate an element from a specific memory pool
 181  * @pool:      pointer to the memory pool which was allocated via
 182  *             mempool_create().
 183  * @gfp_mask:  the usual allocation bitmask.
 184  *
 185  * this function only sleeps if the alloc_fn function sleeps or
 186  * returns NULL. Note that due to preallocation, this function
 187  * *never* fails when called from process contexts. (it might
 188  * fail if called from an IRQ context.)
 189  */
 190 void * mempool_alloc(mempool_t *pool, int gfp_mask)
 191 {
 192         void *element;
 193         unsigned long flags;
 194         DEFINE_WAIT(wait);
 195         int gfp_nowait = gfp_mask & ~(__GFP_WAIT | __GFP_IO);
 196
 197         might_sleep_if(gfp_mask & __GFP_WAIT);
 198 repeat_alloc:
 199         element = pool->alloc(gfp_nowait|__GFP_NOWARN, pool->pool_data);
 200         if (likely(element != NULL))
 201                 return element;
 202
 203         /*
 204          * If the pool is less than 50% full and we can perform effective
 205          * page reclaim then try harder to allocate an element.
 206          */
 207         mb();
 208         if ((gfp_mask & __GFP_FS) && (gfp_mask != gfp_nowait) &&
 209                                 (pool->curr_nr <= pool->min_nr/2)) {
 210                 element = pool->alloc(gfp_mask, pool->pool_data);
 211                 if (likely(element != NULL))
 212                         return element;
 213         }
 214
 215         /*
 216          * Kick the VM at this point.
 217          */
 218         wakeup_bdflush(0);
 219
 220         spin_lock_irqsave(&pool->lock, flags);
 221         if (likely(pool->curr_nr)) {
 222                 element = remove_element(pool);
 223                 spin_unlock_irqrestore(&pool->lock, flags);
 224                 return element;
 225         }
 226         spin_unlock_irqrestore(&pool->lock, flags);
 227
 228         /* We must not sleep in the GFP_ATOMIC case */
 229         if (!(gfp_mask & __GFP_WAIT))
 230                 return NULL;
 231
 232         prepare_to_wait(&pool->wait, &wait, TASK_UNINTERRUPTIBLE);
 233         mb();
 234         if (!pool->curr_nr)
 235                 io_schedule();
 236         finish_wait(&pool->wait, &wait);
 237
 238         goto repeat_alloc;
 239 }
 240 EXPORT_SYMBOL(mempool_alloc);
 241
 242 /**
 243  * mempool_free - return an element to the pool.
 244  * @element:   pool element pointer.
 245  * @pool:      pointer to the memory pool which was allocated via
 246  *             mempool_create().
 247  *
 248  * this function only sleeps if the free_fn() function sleeps.
 249  */
 250 void mempool_free(void *element, mempool_t *pool)
 251 {
 252         unsigned long flags;
 253
 254         mb();
 255         if (pool->curr_nr < pool->min_nr) {
 256                 spin_lock_irqsave(&pool->lock, flags);
 257                 if (pool->curr_nr < pool->min_nr) {
 258                         add_element(pool, element);
 259                         spin_unlock_irqrestore(&pool->lock, flags);
 260                         wake_up(&pool->wait);
 261                         return;
 262                 }
 263                 spin_unlock_irqrestore(&pool->lock, flags);
 264         }
 265         pool->free(element, pool->pool_data);
 266 }
 267 EXPORT_SYMBOL(mempool_free);
 268
 269 /*
 270  * A commonly used alloc and free fn.
 271  */
 272 void *mempool_alloc_slab(int gfp_mask, void *pool_data)
 273 {
 274         kmem_cache_t *mem = (kmem_cache_t *) pool_data;
 275         return kmem_cache_alloc(mem, gfp_mask);
 276 }
 277 EXPORT_SYMBOL(mempool_alloc_slab);
 278
 279 void mempool_free_slab(void *element, void *pool_data)
 280 {
 281         kmem_cache_t *mem = (kmem_cache_t *) pool_data;
 282         kmem_cache_free(mem, element);
 283 }
 284 EXPORT_SYMBOL(mempool_free_slab);