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,
67                   GFP_KERNEL, NUMA_NO_NODE);
68}
69EXPORT_SYMBOL(mempool_create);
70
71mempool_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 = kmalloc_node(sizeof(*pool), gfp_mask | __GFP_ZERO, 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}
107EXPORT_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 */
125int 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    }
178out_unlock:
179    spin_unlock_irqrestore(&pool->lock, flags);
180out:
181    return 0;
182}
183EXPORT_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 */
196void * 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
211repeat_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}
257EXPORT_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 */
267void 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}
319EXPORT_SYMBOL(mempool_free);
320
321/*
322 * A commonly used alloc and free fn.
323 */
324void *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}
329EXPORT_SYMBOL(mempool_alloc_slab);
330
331void mempool_free_slab(void *element, void *pool_data)
332{
333    struct kmem_cache *mem = pool_data;
334    kmem_cache_free(mem, element);
335}
336EXPORT_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 */
342void *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}
347EXPORT_SYMBOL(mempool_kmalloc);
348
349void mempool_kfree(void *element, void *pool_data)
350{
351    kfree(element);
352}
353EXPORT_SYMBOL(mempool_kfree);
354
355/*
356 * A simple mempool-backed page allocator that allocates pages
357 * of the order specified by pool_data.
358 */
359void *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}
364EXPORT_SYMBOL(mempool_alloc_pages);
365
366void mempool_free_pages(void *element, void *pool_data)
367{
368    int order = (int)(long)pool_data;
369    __free_pages(element, order);
370}
371EXPORT_SYMBOL(mempool_free_pages);
372

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