Root/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/kmemleak.h>
14#include <linux/export.h>
15#include <linux/mempool.h>
16#include <linux/blkdev.h>
17#include <linux/writeback.h>
18
19static void add_element(mempool_t *pool, void *element)
20{
21    BUG_ON(pool->curr_nr >= pool->min_nr);
22    pool->elements[pool->curr_nr++] = element;
23}
24
25static void *remove_element(mempool_t *pool)
26{
27    BUG_ON(pool->curr_nr <= 0);
28    return pool->elements[--pool->curr_nr];
29}
30
31/**
32 * mempool_destroy - deallocate a memory pool
33 * @pool: pointer to the memory pool which was allocated via
34 * mempool_create().
35 *
36 * Free all reserved elements in @pool and @pool itself. This function
37 * only sleeps if the free_fn() function sleeps.
38 */
39void mempool_destroy(mempool_t *pool)
40{
41    while (pool->curr_nr) {
42        void *element = remove_element(pool);
43        pool->free(element, pool->pool_data);
44    }
45    kfree(pool->elements);
46    kfree(pool);
47}
48EXPORT_SYMBOL(mempool_destroy);
49
50/**
51 * mempool_create - create a memory pool
52 * @min_nr: the minimum number of elements guaranteed to be
53 * allocated for this pool.
54 * @alloc_fn: user-defined element-allocation function.
55 * @free_fn: user-defined element-freeing function.
56 * @pool_data: optional private data available to the user-defined functions.
57 *
58 * this function creates and allocates a guaranteed size, preallocated
59 * memory pool. The pool can be used from the mempool_alloc() and mempool_free()
60 * functions. This function might sleep. Both the alloc_fn() and the free_fn()
61 * functions might sleep - as long as the mempool_alloc() function is not called
62 * from IRQ contexts.
63 */
64mempool_t *mempool_create(int min_nr, mempool_alloc_t *alloc_fn,
65                mempool_free_t *free_fn, void *pool_data)
66{
67    return mempool_create_node(min_nr,alloc_fn,free_fn, pool_data,
68                   GFP_KERNEL, NUMA_NO_NODE);
69}
70EXPORT_SYMBOL(mempool_create);
71
72mempool_t *mempool_create_node(int min_nr, mempool_alloc_t *alloc_fn,
73                   mempool_free_t *free_fn, void *pool_data,
74                   gfp_t gfp_mask, int node_id)
75{
76    mempool_t *pool;
77    pool = kzalloc_node(sizeof(*pool), gfp_mask, node_id);
78    if (!pool)
79        return NULL;
80    pool->elements = kmalloc_node(min_nr * sizeof(void *),
81                      gfp_mask, node_id);
82    if (!pool->elements) {
83        kfree(pool);
84        return NULL;
85    }
86    spin_lock_init(&pool->lock);
87    pool->min_nr = min_nr;
88    pool->pool_data = pool_data;
89    init_waitqueue_head(&pool->wait);
90    pool->alloc = alloc_fn;
91    pool->free = free_fn;
92
93    /*
94     * First pre-allocate the guaranteed number of buffers.
95     */
96    while (pool->curr_nr < pool->min_nr) {
97        void *element;
98
99        element = pool->alloc(gfp_mask, pool->pool_data);
100        if (unlikely(!element)) {
101            mempool_destroy(pool);
102            return NULL;
103        }
104        add_element(pool, element);
105    }
106    return pool;
107}
108EXPORT_SYMBOL(mempool_create_node);
109
110/**
111 * mempool_resize - resize an existing memory pool
112 * @pool: pointer to the memory pool which was allocated via
113 * mempool_create().
114 * @new_min_nr: the new minimum number of elements guaranteed to be
115 * allocated for this pool.
116 * @gfp_mask: the usual allocation bitmask.
117 *
118 * This function shrinks/grows the pool. In the case of growing,
119 * it cannot be guaranteed that the pool will be grown to the new
120 * size immediately, but new mempool_free() calls will refill it.
121 *
122 * Note, the caller must guarantee that no mempool_destroy is called
123 * while this function is running. mempool_alloc() & mempool_free()
124 * might be called (eg. from IRQ contexts) while this function executes.
125 */
126int mempool_resize(mempool_t *pool, int new_min_nr, gfp_t gfp_mask)
127{
128    void *element;
129    void **new_elements;
130    unsigned long flags;
131
132    BUG_ON(new_min_nr <= 0);
133
134    spin_lock_irqsave(&pool->lock, flags);
135    if (new_min_nr <= pool->min_nr) {
136        while (new_min_nr < pool->curr_nr) {
137            element = remove_element(pool);
138            spin_unlock_irqrestore(&pool->lock, flags);
139            pool->free(element, pool->pool_data);
140            spin_lock_irqsave(&pool->lock, flags);
141        }
142        pool->min_nr = new_min_nr;
143        goto out_unlock;
144    }
145    spin_unlock_irqrestore(&pool->lock, flags);
146
147    /* Grow the pool */
148    new_elements = kmalloc(new_min_nr * sizeof(*new_elements), gfp_mask);
149    if (!new_elements)
150        return -ENOMEM;
151
152    spin_lock_irqsave(&pool->lock, flags);
153    if (unlikely(new_min_nr <= pool->min_nr)) {
154        /* Raced, other resize will do our work */
155        spin_unlock_irqrestore(&pool->lock, flags);
156        kfree(new_elements);
157        goto out;
158    }
159    memcpy(new_elements, pool->elements,
160            pool->curr_nr * sizeof(*new_elements));
161    kfree(pool->elements);
162    pool->elements = new_elements;
163    pool->min_nr = new_min_nr;
164
165    while (pool->curr_nr < pool->min_nr) {
166        spin_unlock_irqrestore(&pool->lock, flags);
167        element = pool->alloc(gfp_mask, pool->pool_data);
168        if (!element)
169            goto out;
170        spin_lock_irqsave(&pool->lock, flags);
171        if (pool->curr_nr < pool->min_nr) {
172            add_element(pool, element);
173        } else {
174            spin_unlock_irqrestore(&pool->lock, flags);
175            pool->free(element, pool->pool_data); /* Raced */
176            goto out;
177        }
178    }
179out_unlock:
180    spin_unlock_irqrestore(&pool->lock, flags);
181out:
182    return 0;
183}
184EXPORT_SYMBOL(mempool_resize);
185
186/**
187 * mempool_alloc - allocate an element from a specific memory pool
188 * @pool: pointer to the memory pool which was allocated via
189 * mempool_create().
190 * @gfp_mask: the usual allocation bitmask.
191 *
192 * this function only sleeps if the alloc_fn() function sleeps or
193 * returns NULL. Note that due to preallocation, this function
194 * *never* fails when called from process contexts. (it might
195 * fail if called from an IRQ context.)
196 * Note: using __GFP_ZERO is not supported.
197 */
198void * mempool_alloc(mempool_t *pool, gfp_t gfp_mask)
199{
200    void *element;
201    unsigned long flags;
202    wait_queue_t wait;
203    gfp_t gfp_temp;
204
205    VM_WARN_ON_ONCE(gfp_mask & __GFP_ZERO);
206    might_sleep_if(gfp_mask & __GFP_WAIT);
207
208    gfp_mask |= __GFP_NOMEMALLOC; /* don't allocate emergency reserves */
209    gfp_mask |= __GFP_NORETRY; /* don't loop in __alloc_pages */
210    gfp_mask |= __GFP_NOWARN; /* failures are OK */
211
212    gfp_temp = gfp_mask & ~(__GFP_WAIT|__GFP_IO);
213
214repeat_alloc:
215
216    element = pool->alloc(gfp_temp, pool->pool_data);
217    if (likely(element != NULL))
218        return element;
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        /* paired with rmb in mempool_free(), read comment there */
225        smp_wmb();
226        /*
227         * Update the allocation stack trace as this is more useful
228         * for debugging.
229         */
230        kmemleak_update_trace(element);
231        return element;
232    }
233
234    /*
235     * We use gfp mask w/o __GFP_WAIT or IO for the first round. If
236     * alloc failed with that and @pool was empty, retry immediately.
237     */
238    if (gfp_temp != gfp_mask) {
239        spin_unlock_irqrestore(&pool->lock, flags);
240        gfp_temp = gfp_mask;
241        goto repeat_alloc;
242    }
243
244    /* We must not sleep if !__GFP_WAIT */
245    if (!(gfp_mask & __GFP_WAIT)) {
246        spin_unlock_irqrestore(&pool->lock, flags);
247        return NULL;
248    }
249
250    /* Let's wait for someone else to return an element to @pool */
251    init_wait(&wait);
252    prepare_to_wait(&pool->wait, &wait, TASK_UNINTERRUPTIBLE);
253
254    spin_unlock_irqrestore(&pool->lock, flags);
255
256    /*
257     * FIXME: this should be io_schedule(). The timeout is there as a
258     * workaround for some DM problems in 2.6.18.
259     */
260    io_schedule_timeout(5*HZ);
261
262    finish_wait(&pool->wait, &wait);
263    goto repeat_alloc;
264}
265EXPORT_SYMBOL(mempool_alloc);
266
267/**
268 * mempool_free - return an element to the pool.
269 * @element: pool element pointer.
270 * @pool: pointer to the memory pool which was allocated via
271 * mempool_create().
272 *
273 * this function only sleeps if the free_fn() function sleeps.
274 */
275void mempool_free(void *element, mempool_t *pool)
276{
277    unsigned long flags;
278
279    if (unlikely(element == NULL))
280        return;
281
282    /*
283     * Paired with the wmb in mempool_alloc(). The preceding read is
284     * for @element and the following @pool->curr_nr. This ensures
285     * that the visible value of @pool->curr_nr is from after the
286     * allocation of @element. This is necessary for fringe cases
287     * where @element was passed to this task without going through
288     * barriers.
289     *
290     * For example, assume @p is %NULL at the beginning and one task
291     * performs "p = mempool_alloc(...);" while another task is doing
292     * "while (!p) cpu_relax(); mempool_free(p, ...);". This function
293     * may end up using curr_nr value which is from before allocation
294     * of @p without the following rmb.
295     */
296    smp_rmb();
297
298    /*
299     * For correctness, we need a test which is guaranteed to trigger
300     * if curr_nr + #allocated == min_nr. Testing curr_nr < min_nr
301     * without locking achieves that and refilling as soon as possible
302     * is desirable.
303     *
304     * Because curr_nr visible here is always a value after the
305     * allocation of @element, any task which decremented curr_nr below
306     * min_nr is guaranteed to see curr_nr < min_nr unless curr_nr gets
307     * incremented to min_nr afterwards. If curr_nr gets incremented
308     * to min_nr after the allocation of @element, the elements
309     * allocated after that are subject to the same guarantee.
310     *
311     * Waiters happen iff curr_nr is 0 and the above guarantee also
312     * ensures that there will be frees which return elements to the
313     * pool waking up the waiters.
314     */
315    if (unlikely(pool->curr_nr < pool->min_nr)) {
316        spin_lock_irqsave(&pool->lock, flags);
317        if (likely(pool->curr_nr < pool->min_nr)) {
318            add_element(pool, element);
319            spin_unlock_irqrestore(&pool->lock, flags);
320            wake_up(&pool->wait);
321            return;
322        }
323        spin_unlock_irqrestore(&pool->lock, flags);
324    }
325    pool->free(element, pool->pool_data);
326}
327EXPORT_SYMBOL(mempool_free);
328
329/*
330 * A commonly used alloc and free fn.
331 */
332void *mempool_alloc_slab(gfp_t gfp_mask, void *pool_data)
333{
334    struct kmem_cache *mem = pool_data;
335    return kmem_cache_alloc(mem, gfp_mask);
336}
337EXPORT_SYMBOL(mempool_alloc_slab);
338
339void mempool_free_slab(void *element, void *pool_data)
340{
341    struct kmem_cache *mem = pool_data;
342    kmem_cache_free(mem, element);
343}
344EXPORT_SYMBOL(mempool_free_slab);
345
346/*
347 * A commonly used alloc and free fn that kmalloc/kfrees the amount of memory
348 * specified by pool_data
349 */
350void *mempool_kmalloc(gfp_t gfp_mask, void *pool_data)
351{
352    size_t size = (size_t)pool_data;
353    return kmalloc(size, gfp_mask);
354}
355EXPORT_SYMBOL(mempool_kmalloc);
356
357void mempool_kfree(void *element, void *pool_data)
358{
359    kfree(element);
360}
361EXPORT_SYMBOL(mempool_kfree);
362
363/*
364 * A simple mempool-backed page allocator that allocates pages
365 * of the order specified by pool_data.
366 */
367void *mempool_alloc_pages(gfp_t gfp_mask, void *pool_data)
368{
369    int order = (int)(long)pool_data;
370    return alloc_pages(gfp_mask, order);
371}
372EXPORT_SYMBOL(mempool_alloc_pages);
373
374void mempool_free_pages(void *element, void *pool_data)
375{
376    int order = (int)(long)pool_data;
377    __free_pages(element, order);
378}
379EXPORT_SYMBOL(mempool_free_pages);
380

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