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

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