Root/lib/percpu_ida.c

1/*
2 * Percpu IDA library
3 *
4 * Copyright (C) 2013 Datera, Inc. Kent Overstreet
5 *
6 * This program is free software; you can redistribute it and/or
7 * modify it under the terms of the GNU General Public License as
8 * published by the Free Software Foundation; either version 2, or (at
9 * your option) any later version.
10 *
11 * This program is distributed in the hope that it will be useful, but
12 * WITHOUT ANY WARRANTY; without even the implied warranty of
13 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
14 * General Public License for more details.
15 */
16
17#include <linux/bitmap.h>
18#include <linux/bitops.h>
19#include <linux/bug.h>
20#include <linux/err.h>
21#include <linux/export.h>
22#include <linux/hardirq.h>
23#include <linux/idr.h>
24#include <linux/init.h>
25#include <linux/kernel.h>
26#include <linux/percpu.h>
27#include <linux/sched.h>
28#include <linux/slab.h>
29#include <linux/string.h>
30#include <linux/spinlock.h>
31#include <linux/percpu_ida.h>
32
33struct percpu_ida_cpu {
34    /*
35     * Even though this is percpu, we need a lock for tag stealing by remote
36     * CPUs:
37     */
38    spinlock_t lock;
39
40    /* nr_free/freelist form a stack of free IDs */
41    unsigned nr_free;
42    unsigned freelist[];
43};
44
45static inline void move_tags(unsigned *dst, unsigned *dst_nr,
46                 unsigned *src, unsigned *src_nr,
47                 unsigned nr)
48{
49    *src_nr -= nr;
50    memcpy(dst + *dst_nr, src + *src_nr, sizeof(unsigned) * nr);
51    *dst_nr += nr;
52}
53
54/*
55 * Try to steal tags from a remote cpu's percpu freelist.
56 *
57 * We first check how many percpu freelists have tags - we don't steal tags
58 * unless enough percpu freelists have tags on them that it's possible more than
59 * half the total tags could be stuck on remote percpu freelists.
60 *
61 * Then we iterate through the cpus until we find some tags - we don't attempt
62 * to find the "best" cpu to steal from, to keep cacheline bouncing to a
63 * minimum.
64 */
65static inline void steal_tags(struct percpu_ida *pool,
66                  struct percpu_ida_cpu *tags)
67{
68    unsigned cpus_have_tags, cpu = pool->cpu_last_stolen;
69    struct percpu_ida_cpu *remote;
70
71    for (cpus_have_tags = cpumask_weight(&pool->cpus_have_tags);
72         cpus_have_tags * pool->percpu_max_size > pool->nr_tags / 2;
73         cpus_have_tags--) {
74        cpu = cpumask_next(cpu, &pool->cpus_have_tags);
75
76        if (cpu >= nr_cpu_ids) {
77            cpu = cpumask_first(&pool->cpus_have_tags);
78            if (cpu >= nr_cpu_ids)
79                BUG();
80        }
81
82        pool->cpu_last_stolen = cpu;
83        remote = per_cpu_ptr(pool->tag_cpu, cpu);
84
85        cpumask_clear_cpu(cpu, &pool->cpus_have_tags);
86
87        if (remote == tags)
88            continue;
89
90        spin_lock(&remote->lock);
91
92        if (remote->nr_free) {
93            memcpy(tags->freelist,
94                   remote->freelist,
95                   sizeof(unsigned) * remote->nr_free);
96
97            tags->nr_free = remote->nr_free;
98            remote->nr_free = 0;
99        }
100
101        spin_unlock(&remote->lock);
102
103        if (tags->nr_free)
104            break;
105    }
106}
107
108/*
109 * Pop up to IDA_PCPU_BATCH_MOVE IDs off the global freelist, and push them onto
110 * our percpu freelist:
111 */
112static inline void alloc_global_tags(struct percpu_ida *pool,
113                     struct percpu_ida_cpu *tags)
114{
115    move_tags(tags->freelist, &tags->nr_free,
116          pool->freelist, &pool->nr_free,
117          min(pool->nr_free, pool->percpu_batch_size));
118}
119
120static inline unsigned alloc_local_tag(struct percpu_ida_cpu *tags)
121{
122    int tag = -ENOSPC;
123
124    spin_lock(&tags->lock);
125    if (tags->nr_free)
126        tag = tags->freelist[--tags->nr_free];
127    spin_unlock(&tags->lock);
128
129    return tag;
130}
131
132/**
133 * percpu_ida_alloc - allocate a tag
134 * @pool: pool to allocate from
135 * @gfp: gfp flags
136 *
137 * Returns a tag - an integer in the range [0..nr_tags) (passed to
138 * tag_pool_init()), or otherwise -ENOSPC on allocation failure.
139 *
140 * Safe to be called from interrupt context (assuming it isn't passed
141 * __GFP_WAIT, of course).
142 *
143 * @gfp indicates whether or not to wait until a free id is available (it's not
144 * used for internal memory allocations); thus if passed __GFP_WAIT we may sleep
145 * however long it takes until another thread frees an id (same semantics as a
146 * mempool).
147 *
148 * Will not fail if passed __GFP_WAIT.
149 */
150int percpu_ida_alloc(struct percpu_ida *pool, gfp_t gfp)
151{
152    DEFINE_WAIT(wait);
153    struct percpu_ida_cpu *tags;
154    unsigned long flags;
155    int tag;
156
157    local_irq_save(flags);
158    tags = this_cpu_ptr(pool->tag_cpu);
159
160    /* Fastpath */
161    tag = alloc_local_tag(tags);
162    if (likely(tag >= 0)) {
163        local_irq_restore(flags);
164        return tag;
165    }
166
167    while (1) {
168        spin_lock(&pool->lock);
169
170        /*
171         * prepare_to_wait() must come before steal_tags(), in case
172         * percpu_ida_free() on another cpu flips a bit in
173         * cpus_have_tags
174         *
175         * global lock held and irqs disabled, don't need percpu lock
176         */
177        prepare_to_wait(&pool->wait, &wait, TASK_UNINTERRUPTIBLE);
178
179        if (!tags->nr_free)
180            alloc_global_tags(pool, tags);
181        if (!tags->nr_free)
182            steal_tags(pool, tags);
183
184        if (tags->nr_free) {
185            tag = tags->freelist[--tags->nr_free];
186            if (tags->nr_free)
187                cpumask_set_cpu(smp_processor_id(),
188                        &pool->cpus_have_tags);
189        }
190
191        spin_unlock(&pool->lock);
192        local_irq_restore(flags);
193
194        if (tag >= 0 || !(gfp & __GFP_WAIT))
195            break;
196
197        schedule();
198
199        local_irq_save(flags);
200        tags = this_cpu_ptr(pool->tag_cpu);
201    }
202
203    finish_wait(&pool->wait, &wait);
204    return tag;
205}
206EXPORT_SYMBOL_GPL(percpu_ida_alloc);
207
208/**
209 * percpu_ida_free - free a tag
210 * @pool: pool @tag was allocated from
211 * @tag: a tag previously allocated with percpu_ida_alloc()
212 *
213 * Safe to be called from interrupt context.
214 */
215void percpu_ida_free(struct percpu_ida *pool, unsigned tag)
216{
217    struct percpu_ida_cpu *tags;
218    unsigned long flags;
219    unsigned nr_free;
220
221    BUG_ON(tag >= pool->nr_tags);
222
223    local_irq_save(flags);
224    tags = this_cpu_ptr(pool->tag_cpu);
225
226    spin_lock(&tags->lock);
227    tags->freelist[tags->nr_free++] = tag;
228
229    nr_free = tags->nr_free;
230    spin_unlock(&tags->lock);
231
232    if (nr_free == 1) {
233        cpumask_set_cpu(smp_processor_id(),
234                &pool->cpus_have_tags);
235        wake_up(&pool->wait);
236    }
237
238    if (nr_free == pool->percpu_max_size) {
239        spin_lock(&pool->lock);
240
241        /*
242         * Global lock held and irqs disabled, don't need percpu
243         * lock
244         */
245        if (tags->nr_free == pool->percpu_max_size) {
246            move_tags(pool->freelist, &pool->nr_free,
247                  tags->freelist, &tags->nr_free,
248                  pool->percpu_batch_size);
249
250            wake_up(&pool->wait);
251        }
252        spin_unlock(&pool->lock);
253    }
254
255    local_irq_restore(flags);
256}
257EXPORT_SYMBOL_GPL(percpu_ida_free);
258
259/**
260 * percpu_ida_destroy - release a tag pool's resources
261 * @pool: pool to free
262 *
263 * Frees the resources allocated by percpu_ida_init().
264 */
265void percpu_ida_destroy(struct percpu_ida *pool)
266{
267    free_percpu(pool->tag_cpu);
268    free_pages((unsigned long) pool->freelist,
269           get_order(pool->nr_tags * sizeof(unsigned)));
270}
271EXPORT_SYMBOL_GPL(percpu_ida_destroy);
272
273/**
274 * percpu_ida_init - initialize a percpu tag pool
275 * @pool: pool to initialize
276 * @nr_tags: number of tags that will be available for allocation
277 *
278 * Initializes @pool so that it can be used to allocate tags - integers in the
279 * range [0, nr_tags). Typically, they'll be used by driver code to refer to a
280 * preallocated array of tag structures.
281 *
282 * Allocation is percpu, but sharding is limited by nr_tags - for best
283 * performance, the workload should not span more cpus than nr_tags / 128.
284 */
285int __percpu_ida_init(struct percpu_ida *pool, unsigned long nr_tags,
286    unsigned long max_size, unsigned long batch_size)
287{
288    unsigned i, cpu, order;
289
290    memset(pool, 0, sizeof(*pool));
291
292    init_waitqueue_head(&pool->wait);
293    spin_lock_init(&pool->lock);
294    pool->nr_tags = nr_tags;
295    pool->percpu_max_size = max_size;
296    pool->percpu_batch_size = batch_size;
297
298    /* Guard against overflow */
299    if (nr_tags > (unsigned) INT_MAX + 1) {
300        pr_err("percpu_ida_init(): nr_tags too large\n");
301        return -EINVAL;
302    }
303
304    order = get_order(nr_tags * sizeof(unsigned));
305    pool->freelist = (void *) __get_free_pages(GFP_KERNEL, order);
306    if (!pool->freelist)
307        return -ENOMEM;
308
309    for (i = 0; i < nr_tags; i++)
310        pool->freelist[i] = i;
311
312    pool->nr_free = nr_tags;
313
314    pool->tag_cpu = __alloc_percpu(sizeof(struct percpu_ida_cpu) +
315                       pool->percpu_max_size * sizeof(unsigned),
316                       sizeof(unsigned));
317    if (!pool->tag_cpu)
318        goto err;
319
320    for_each_possible_cpu(cpu)
321        spin_lock_init(&per_cpu_ptr(pool->tag_cpu, cpu)->lock);
322
323    return 0;
324err:
325    percpu_ida_destroy(pool);
326    return -ENOMEM;
327}
328EXPORT_SYMBOL_GPL(__percpu_ida_init);
329
330/**
331 * percpu_ida_for_each_free - iterate free ids of a pool
332 * @pool: pool to iterate
333 * @fn: interate callback function
334 * @data: parameter for @fn
335 *
336 * Note, this doesn't guarantee to iterate all free ids restrictly. Some free
337 * ids might be missed, some might be iterated duplicated, and some might
338 * be iterated and not free soon.
339 */
340int percpu_ida_for_each_free(struct percpu_ida *pool, percpu_ida_cb fn,
341    void *data)
342{
343    unsigned long flags;
344    struct percpu_ida_cpu *remote;
345    unsigned cpu, i, err = 0;
346
347    local_irq_save(flags);
348    for_each_possible_cpu(cpu) {
349        remote = per_cpu_ptr(pool->tag_cpu, cpu);
350        spin_lock(&remote->lock);
351        for (i = 0; i < remote->nr_free; i++) {
352            err = fn(remote->freelist[i], data);
353            if (err)
354                break;
355        }
356        spin_unlock(&remote->lock);
357        if (err)
358            goto out;
359    }
360
361    spin_lock(&pool->lock);
362    for (i = 0; i < pool->nr_free; i++) {
363        err = fn(pool->freelist[i], data);
364        if (err)
365            break;
366    }
367    spin_unlock(&pool->lock);
368out:
369    local_irq_restore(flags);
370    return err;
371}
372EXPORT_SYMBOL_GPL(percpu_ida_for_each_free);
373
374/**
375 * percpu_ida_free_tags - return free tags number of a specific cpu or global pool
376 * @pool: pool related
377 * @cpu: specific cpu or global pool if @cpu == nr_cpu_ids
378 *
379 * Note: this just returns a snapshot of free tags number.
380 */
381unsigned percpu_ida_free_tags(struct percpu_ida *pool, int cpu)
382{
383    struct percpu_ida_cpu *remote;
384    if (cpu == nr_cpu_ids)
385        return pool->nr_free;
386    remote = per_cpu_ptr(pool->tag_cpu, cpu);
387    return remote->nr_free;
388}
389EXPORT_SYMBOL_GPL(percpu_ida_free_tags);
390

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