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/export.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 /**
  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  */
  38 void 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 }
  47 EXPORT_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  */
  63 mempool_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 }
  69 EXPORT_SYMBOL(mempool_create);
  70
  71 mempool_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 }
 107 EXPORT_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  */
 125 int 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         }
 178 out_unlock:
 179         spin_unlock_irqrestore(&pool->lock, flags);
 180 out:
 181         return 0;
 182 }
 183 EXPORT_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  */
 196 void * 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
 211 repeat_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 }
 257 EXPORT_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  */
 267 void 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 }
 319 EXPORT_SYMBOL(mempool_free);
 320
 321 /*
 322  * A commonly used alloc and free fn.
 323  */
 324 void *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 }
 329 EXPORT_SYMBOL(mempool_alloc_slab);
 330
 331 void mempool_free_slab(void *element, void *pool_data)
 332 {
 333         struct kmem_cache *mem = pool_data;
 334         kmem_cache_free(mem, element);
 335 }
 336 EXPORT_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  */
 342 void *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 }
 347 EXPORT_SYMBOL(mempool_kmalloc);
 348
 349 void mempool_kfree(void *element, void *pool_data)
 350 {
 351         kfree(element);
 352 }
 353 EXPORT_SYMBOL(mempool_kfree);
 354
 355 /*
 356  * A simple mempool-backed page allocator that allocates pages
 357  * of the order specified by pool_data.
 358  */
 359 void *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 }
 364 EXPORT_SYMBOL(mempool_alloc_pages);
 365
 366 void mempool_free_pages(void *element, void *pool_data)
 367 {
 368         int order = (int)(long)pool_data;
 369         __free_pages(element, order);
 370 }
 371 EXPORT_SYMBOL(mempool_free_pages);