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Linux/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/init.h>
 23 #include <linux/kernel.h>
 24 #include <linux/percpu.h>
 25 #include <linux/sched.h>
 26 #include <linux/string.h>
 27 #include <linux/spinlock.h>
 28 #include <linux/percpu_ida.h>
 29 
 30 struct percpu_ida_cpu {
 31         /*
 32          * Even though this is percpu, we need a lock for tag stealing by remote
 33          * CPUs:
 34          */
 35         spinlock_t                      lock;
 36 
 37         /* nr_free/freelist form a stack of free IDs */
 38         unsigned                        nr_free;
 39         unsigned                        freelist[];
 40 };
 41 
 42 static inline void move_tags(unsigned *dst, unsigned *dst_nr,
 43                              unsigned *src, unsigned *src_nr,
 44                              unsigned nr)
 45 {
 46         *src_nr -= nr;
 47         memcpy(dst + *dst_nr, src + *src_nr, sizeof(unsigned) * nr);
 48         *dst_nr += nr;
 49 }
 50 
 51 /*
 52  * Try to steal tags from a remote cpu's percpu freelist.
 53  *
 54  * We first check how many percpu freelists have tags
 55  *
 56  * Then we iterate through the cpus until we find some tags - we don't attempt
 57  * to find the "best" cpu to steal from, to keep cacheline bouncing to a
 58  * minimum.
 59  */
 60 static inline void steal_tags(struct percpu_ida *pool,
 61                               struct percpu_ida_cpu *tags)
 62 {
 63         unsigned cpus_have_tags, cpu = pool->cpu_last_stolen;
 64         struct percpu_ida_cpu *remote;
 65 
 66         for (cpus_have_tags = cpumask_weight(&pool->cpus_have_tags);
 67              cpus_have_tags; cpus_have_tags--) {
 68                 cpu = cpumask_next(cpu, &pool->cpus_have_tags);
 69 
 70                 if (cpu >= nr_cpu_ids) {
 71                         cpu = cpumask_first(&pool->cpus_have_tags);
 72                         if (cpu >= nr_cpu_ids)
 73                                 BUG();
 74                 }
 75 
 76                 pool->cpu_last_stolen = cpu;
 77                 remote = per_cpu_ptr(pool->tag_cpu, cpu);
 78 
 79                 cpumask_clear_cpu(cpu, &pool->cpus_have_tags);
 80 
 81                 if (remote == tags)
 82                         continue;
 83 
 84                 spin_lock(&remote->lock);
 85 
 86                 if (remote->nr_free) {
 87                         memcpy(tags->freelist,
 88                                remote->freelist,
 89                                sizeof(unsigned) * remote->nr_free);
 90 
 91                         tags->nr_free = remote->nr_free;
 92                         remote->nr_free = 0;
 93                 }
 94 
 95                 spin_unlock(&remote->lock);
 96 
 97                 if (tags->nr_free)
 98                         break;
 99         }
100 }
101 
102 /*
103  * Pop up to IDA_PCPU_BATCH_MOVE IDs off the global freelist, and push them onto
104  * our percpu freelist:
105  */
106 static inline void alloc_global_tags(struct percpu_ida *pool,
107                                      struct percpu_ida_cpu *tags)
108 {
109         move_tags(tags->freelist, &tags->nr_free,
110                   pool->freelist, &pool->nr_free,
111                   min(pool->nr_free, pool->percpu_batch_size));
112 }
113 
114 static inline unsigned alloc_local_tag(struct percpu_ida_cpu *tags)
115 {
116         int tag = -ENOSPC;
117 
118         spin_lock(&tags->lock);
119         if (tags->nr_free)
120                 tag = tags->freelist[--tags->nr_free];
121         spin_unlock(&tags->lock);
122 
123         return tag;
124 }
125 
126 /**
127  * percpu_ida_alloc - allocate a tag
128  * @pool: pool to allocate from
129  * @state: task state for prepare_to_wait
130  *
131  * Returns a tag - an integer in the range [0..nr_tags) (passed to
132  * tag_pool_init()), or otherwise -ENOSPC on allocation failure.
133  *
134  * Safe to be called from interrupt context (assuming it isn't passed
135  * TASK_UNINTERRUPTIBLE | TASK_INTERRUPTIBLE, of course).
136  *
137  * @gfp indicates whether or not to wait until a free id is available (it's not
138  * used for internal memory allocations); thus if passed __GFP_RECLAIM we may sleep
139  * however long it takes until another thread frees an id (same semantics as a
140  * mempool).
141  *
142  * Will not fail if passed TASK_UNINTERRUPTIBLE | TASK_INTERRUPTIBLE.
143  */
144 int percpu_ida_alloc(struct percpu_ida *pool, int state)
145 {
146         DEFINE_WAIT(wait);
147         struct percpu_ida_cpu *tags;
148         unsigned long flags;
149         int tag;
150 
151         local_irq_save(flags);
152         tags = this_cpu_ptr(pool->tag_cpu);
153 
154         /* Fastpath */
155         tag = alloc_local_tag(tags);
156         if (likely(tag >= 0)) {
157                 local_irq_restore(flags);
158                 return tag;
159         }
160 
161         while (1) {
162                 spin_lock(&pool->lock);
163 
164                 /*
165                  * prepare_to_wait() must come before steal_tags(), in case
166                  * percpu_ida_free() on another cpu flips a bit in
167                  * cpus_have_tags
168                  *
169                  * global lock held and irqs disabled, don't need percpu lock
170                  */
171                 if (state != TASK_RUNNING)
172                         prepare_to_wait(&pool->wait, &wait, state);
173 
174                 if (!tags->nr_free)
175                         alloc_global_tags(pool, tags);
176                 if (!tags->nr_free)
177                         steal_tags(pool, tags);
178 
179                 if (tags->nr_free) {
180                         tag = tags->freelist[--tags->nr_free];
181                         if (tags->nr_free)
182                                 cpumask_set_cpu(smp_processor_id(),
183                                                 &pool->cpus_have_tags);
184                 }
185 
186                 spin_unlock(&pool->lock);
187                 local_irq_restore(flags);
188 
189                 if (tag >= 0 || state == TASK_RUNNING)
190                         break;
191 
192                 if (signal_pending_state(state, current)) {
193                         tag = -ERESTARTSYS;
194                         break;
195                 }
196 
197                 schedule();
198 
199                 local_irq_save(flags);
200                 tags = this_cpu_ptr(pool->tag_cpu);
201         }
202         if (state != TASK_RUNNING)
203                 finish_wait(&pool->wait, &wait);
204 
205         return tag;
206 }
207 EXPORT_SYMBOL_GPL(percpu_ida_alloc);
208 
209 /**
210  * percpu_ida_free - free a tag
211  * @pool: pool @tag was allocated from
212  * @tag: a tag previously allocated with percpu_ida_alloc()
213  *
214  * Safe to be called from interrupt context.
215  */
216 void percpu_ida_free(struct percpu_ida *pool, unsigned tag)
217 {
218         struct percpu_ida_cpu *tags;
219         unsigned long flags;
220         unsigned nr_free;
221 
222         BUG_ON(tag >= pool->nr_tags);
223 
224         local_irq_save(flags);
225         tags = this_cpu_ptr(pool->tag_cpu);
226 
227         spin_lock(&tags->lock);
228         tags->freelist[tags->nr_free++] = tag;
229 
230         nr_free = tags->nr_free;
231         spin_unlock(&tags->lock);
232 
233         if (nr_free == 1) {
234                 cpumask_set_cpu(smp_processor_id(),
235                                 &pool->cpus_have_tags);
236                 wake_up(&pool->wait);
237         }
238 
239         if (nr_free == pool->percpu_max_size) {
240                 spin_lock(&pool->lock);
241 
242                 /*
243                  * Global lock held and irqs disabled, don't need percpu
244                  * lock
245                  */
246                 if (tags->nr_free == pool->percpu_max_size) {
247                         move_tags(pool->freelist, &pool->nr_free,
248                                   tags->freelist, &tags->nr_free,
249                                   pool->percpu_batch_size);
250 
251                         wake_up(&pool->wait);
252                 }
253                 spin_unlock(&pool->lock);
254         }
255 
256         local_irq_restore(flags);
257 }
258 EXPORT_SYMBOL_GPL(percpu_ida_free);
259 
260 /**
261  * percpu_ida_destroy - release a tag pool's resources
262  * @pool: pool to free
263  *
264  * Frees the resources allocated by percpu_ida_init().
265  */
266 void percpu_ida_destroy(struct percpu_ida *pool)
267 {
268         free_percpu(pool->tag_cpu);
269         free_pages((unsigned long) pool->freelist,
270                    get_order(pool->nr_tags * sizeof(unsigned)));
271 }
272 EXPORT_SYMBOL_GPL(percpu_ida_destroy);
273 
274 /**
275  * percpu_ida_init - initialize a percpu tag pool
276  * @pool: pool to initialize
277  * @nr_tags: number of tags that will be available for allocation
278  *
279  * Initializes @pool so that it can be used to allocate tags - integers in the
280  * range [0, nr_tags). Typically, they'll be used by driver code to refer to a
281  * preallocated array of tag structures.
282  *
283  * Allocation is percpu, but sharding is limited by nr_tags - for best
284  * performance, the workload should not span more cpus than nr_tags / 128.
285  */
286 int __percpu_ida_init(struct percpu_ida *pool, unsigned long nr_tags,
287         unsigned long max_size, unsigned long batch_size)
288 {
289         unsigned i, cpu, order;
290 
291         memset(pool, 0, sizeof(*pool));
292 
293         init_waitqueue_head(&pool->wait);
294         spin_lock_init(&pool->lock);
295         pool->nr_tags = nr_tags;
296         pool->percpu_max_size = max_size;
297         pool->percpu_batch_size = batch_size;
298 
299         /* Guard against overflow */
300         if (nr_tags > (unsigned) INT_MAX + 1) {
301                 pr_err("percpu_ida_init(): nr_tags too large\n");
302                 return -EINVAL;
303         }
304 
305         order = get_order(nr_tags * sizeof(unsigned));
306         pool->freelist = (void *) __get_free_pages(GFP_KERNEL, order);
307         if (!pool->freelist)
308                 return -ENOMEM;
309 
310         for (i = 0; i < nr_tags; i++)
311                 pool->freelist[i] = i;
312 
313         pool->nr_free = nr_tags;
314 
315         pool->tag_cpu = __alloc_percpu(sizeof(struct percpu_ida_cpu) +
316                                        pool->percpu_max_size * sizeof(unsigned),
317                                        sizeof(unsigned));
318         if (!pool->tag_cpu)
319                 goto err;
320 
321         for_each_possible_cpu(cpu)
322                 spin_lock_init(&per_cpu_ptr(pool->tag_cpu, cpu)->lock);
323 
324         return 0;
325 err:
326         percpu_ida_destroy(pool);
327         return -ENOMEM;
328 }
329 EXPORT_SYMBOL_GPL(__percpu_ida_init);
330 
331 /**
332  * percpu_ida_for_each_free - iterate free ids of a pool
333  * @pool: pool to iterate
334  * @fn: interate callback function
335  * @data: parameter for @fn
336  *
337  * Note, this doesn't guarantee to iterate all free ids restrictly. Some free
338  * ids might be missed, some might be iterated duplicated, and some might
339  * be iterated and not free soon.
340  */
341 int percpu_ida_for_each_free(struct percpu_ida *pool, percpu_ida_cb fn,
342         void *data)
343 {
344         unsigned long flags;
345         struct percpu_ida_cpu *remote;
346         unsigned cpu, i, err = 0;
347 
348         local_irq_save(flags);
349         for_each_possible_cpu(cpu) {
350                 remote = per_cpu_ptr(pool->tag_cpu, cpu);
351                 spin_lock(&remote->lock);
352                 for (i = 0; i < remote->nr_free; i++) {
353                         err = fn(remote->freelist[i], data);
354                         if (err)
355                                 break;
356                 }
357                 spin_unlock(&remote->lock);
358                 if (err)
359                         goto out;
360         }
361 
362         spin_lock(&pool->lock);
363         for (i = 0; i < pool->nr_free; i++) {
364                 err = fn(pool->freelist[i], data);
365                 if (err)
366                         break;
367         }
368         spin_unlock(&pool->lock);
369 out:
370         local_irq_restore(flags);
371         return err;
372 }
373 EXPORT_SYMBOL_GPL(percpu_ida_for_each_free);
374 
375 /**
376  * percpu_ida_free_tags - return free tags number of a specific cpu or global pool
377  * @pool: pool related
378  * @cpu: specific cpu or global pool if @cpu == nr_cpu_ids
379  *
380  * Note: this just returns a snapshot of free tags number.
381  */
382 unsigned percpu_ida_free_tags(struct percpu_ida *pool, int cpu)
383 {
384         struct percpu_ida_cpu *remote;
385         if (cpu == nr_cpu_ids)
386                 return pool->nr_free;
387         remote = per_cpu_ptr(pool->tag_cpu, cpu);
388         return remote->nr_free;
389 }
390 EXPORT_SYMBOL_GPL(percpu_ida_free_tags);
391 

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