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/mm.h>
18 #include <linux/bitmap.h>
19 #include <linux/bitops.h>
20 #include <linux/bug.h>
21 #include <linux/err.h>
22 #include <linux/export.h>
23 #include <linux/init.h>
24 #include <linux/kernel.h>
25 #include <linux/percpu.h>
26 #include <linux/sched/signal.h>
27 #include <linux/string.h>
28 #include <linux/spinlock.h>
29 #include <linux/percpu_ida.h>
30
31 struct percpu_ida_cpu {
32 /*
33 * Even though this is percpu, we need a lock for tag stealing by remote
34 * CPUs:
35 */
36 spinlock_t lock;
37
38 /* nr_free/freelist form a stack of free IDs */
39 unsigned nr_free;
40 unsigned freelist[];
41 };
42
move_tags(unsigned * dst,unsigned * dst_nr,unsigned * src,unsigned * src_nr,unsigned nr)43 static inline void move_tags(unsigned *dst, unsigned *dst_nr,
44 unsigned *src, unsigned *src_nr,
45 unsigned nr)
46 {
47 *src_nr -= nr;
48 memcpy(dst + *dst_nr, src + *src_nr, sizeof(unsigned) * nr);
49 *dst_nr += nr;
50 }
51
52 /*
53 * Try to steal tags from a remote cpu's percpu freelist.
54 *
55 * We first check how many percpu freelists have tags
56 *
57 * Then we iterate through the cpus until we find some tags - we don't attempt
58 * to find the "best" cpu to steal from, to keep cacheline bouncing to a
59 * minimum.
60 */
steal_tags(struct percpu_ida * pool,struct percpu_ida_cpu * tags)61 static inline void steal_tags(struct percpu_ida *pool,
62 struct percpu_ida_cpu *tags)
63 {
64 unsigned cpus_have_tags, cpu = pool->cpu_last_stolen;
65 struct percpu_ida_cpu *remote;
66
67 for (cpus_have_tags = cpumask_weight(&pool->cpus_have_tags);
68 cpus_have_tags; cpus_have_tags--) {
69 cpu = cpumask_next(cpu, &pool->cpus_have_tags);
70
71 if (cpu >= nr_cpu_ids) {
72 cpu = cpumask_first(&pool->cpus_have_tags);
73 if (cpu >= nr_cpu_ids)
74 BUG();
75 }
76
77 pool->cpu_last_stolen = cpu;
78 remote = per_cpu_ptr(pool->tag_cpu, cpu);
79
80 cpumask_clear_cpu(cpu, &pool->cpus_have_tags);
81
82 if (remote == tags)
83 continue;
84
85 spin_lock(&remote->lock);
86
87 if (remote->nr_free) {
88 memcpy(tags->freelist,
89 remote->freelist,
90 sizeof(unsigned) * remote->nr_free);
91
92 tags->nr_free = remote->nr_free;
93 remote->nr_free = 0;
94 }
95
96 spin_unlock(&remote->lock);
97
98 if (tags->nr_free)
99 break;
100 }
101 }
102
103 /*
104 * Pop up to IDA_PCPU_BATCH_MOVE IDs off the global freelist, and push them onto
105 * our percpu freelist:
106 */
alloc_global_tags(struct percpu_ida * pool,struct percpu_ida_cpu * tags)107 static inline void alloc_global_tags(struct percpu_ida *pool,
108 struct percpu_ida_cpu *tags)
109 {
110 move_tags(tags->freelist, &tags->nr_free,
111 pool->freelist, &pool->nr_free,
112 min(pool->nr_free, pool->percpu_batch_size));
113 }
114
alloc_local_tag(struct percpu_ida_cpu * tags)115 static inline unsigned alloc_local_tag(struct percpu_ida_cpu *tags)
116 {
117 int tag = -ENOSPC;
118
119 spin_lock(&tags->lock);
120 if (tags->nr_free)
121 tag = tags->freelist[--tags->nr_free];
122 spin_unlock(&tags->lock);
123
124 return tag;
125 }
126
127 /**
128 * percpu_ida_alloc - allocate a tag
129 * @pool: pool to allocate from
130 * @state: task state for prepare_to_wait
131 *
132 * Returns a tag - an integer in the range [0..nr_tags) (passed to
133 * tag_pool_init()), or otherwise -ENOSPC on allocation failure.
134 *
135 * Safe to be called from interrupt context (assuming it isn't passed
136 * TASK_UNINTERRUPTIBLE | TASK_INTERRUPTIBLE, of course).
137 *
138 * @gfp indicates whether or not to wait until a free id is available (it's not
139 * used for internal memory allocations); thus if passed __GFP_RECLAIM we may sleep
140 * however long it takes until another thread frees an id (same semantics as a
141 * mempool).
142 *
143 * Will not fail if passed TASK_UNINTERRUPTIBLE | TASK_INTERRUPTIBLE.
144 */
percpu_ida_alloc(struct percpu_ida * pool,int state)145 int percpu_ida_alloc(struct percpu_ida *pool, int state)
146 {
147 DEFINE_WAIT(wait);
148 struct percpu_ida_cpu *tags;
149 unsigned long flags;
150 int tag;
151
152 local_irq_save(flags);
153 tags = this_cpu_ptr(pool->tag_cpu);
154
155 /* Fastpath */
156 tag = alloc_local_tag(tags);
157 if (likely(tag >= 0)) {
158 local_irq_restore(flags);
159 return tag;
160 }
161
162 while (1) {
163 spin_lock(&pool->lock);
164
165 /*
166 * prepare_to_wait() must come before steal_tags(), in case
167 * percpu_ida_free() on another cpu flips a bit in
168 * cpus_have_tags
169 *
170 * global lock held and irqs disabled, don't need percpu lock
171 */
172 if (state != TASK_RUNNING)
173 prepare_to_wait(&pool->wait, &wait, state);
174
175 if (!tags->nr_free)
176 alloc_global_tags(pool, tags);
177 if (!tags->nr_free)
178 steal_tags(pool, tags);
179
180 if (tags->nr_free) {
181 tag = tags->freelist[--tags->nr_free];
182 if (tags->nr_free)
183 cpumask_set_cpu(smp_processor_id(),
184 &pool->cpus_have_tags);
185 }
186
187 spin_unlock(&pool->lock);
188 local_irq_restore(flags);
189
190 if (tag >= 0 || state == TASK_RUNNING)
191 break;
192
193 if (signal_pending_state(state, current)) {
194 tag = -ERESTARTSYS;
195 break;
196 }
197
198 schedule();
199
200 local_irq_save(flags);
201 tags = this_cpu_ptr(pool->tag_cpu);
202 }
203 if (state != TASK_RUNNING)
204 finish_wait(&pool->wait, &wait);
205
206 return tag;
207 }
208 EXPORT_SYMBOL_GPL(percpu_ida_alloc);
209
210 /**
211 * percpu_ida_free - free a tag
212 * @pool: pool @tag was allocated from
213 * @tag: a tag previously allocated with percpu_ida_alloc()
214 *
215 * Safe to be called from interrupt context.
216 */
percpu_ida_free(struct percpu_ida * pool,unsigned tag)217 void percpu_ida_free(struct percpu_ida *pool, unsigned tag)
218 {
219 struct percpu_ida_cpu *tags;
220 unsigned long flags;
221 unsigned nr_free;
222
223 BUG_ON(tag >= pool->nr_tags);
224
225 local_irq_save(flags);
226 tags = this_cpu_ptr(pool->tag_cpu);
227
228 spin_lock(&tags->lock);
229 tags->freelist[tags->nr_free++] = tag;
230
231 nr_free = tags->nr_free;
232 spin_unlock(&tags->lock);
233
234 if (nr_free == 1) {
235 cpumask_set_cpu(smp_processor_id(),
236 &pool->cpus_have_tags);
237 wake_up(&pool->wait);
238 }
239
240 if (nr_free == pool->percpu_max_size) {
241 spin_lock(&pool->lock);
242
243 /*
244 * Global lock held and irqs disabled, don't need percpu
245 * lock
246 */
247 if (tags->nr_free == pool->percpu_max_size) {
248 move_tags(pool->freelist, &pool->nr_free,
249 tags->freelist, &tags->nr_free,
250 pool->percpu_batch_size);
251
252 wake_up(&pool->wait);
253 }
254 spin_unlock(&pool->lock);
255 }
256
257 local_irq_restore(flags);
258 }
259 EXPORT_SYMBOL_GPL(percpu_ida_free);
260
261 /**
262 * percpu_ida_destroy - release a tag pool's resources
263 * @pool: pool to free
264 *
265 * Frees the resources allocated by percpu_ida_init().
266 */
percpu_ida_destroy(struct percpu_ida * pool)267 void percpu_ida_destroy(struct percpu_ida *pool)
268 {
269 free_percpu(pool->tag_cpu);
270 free_pages((unsigned long) pool->freelist,
271 get_order(pool->nr_tags * sizeof(unsigned)));
272 }
273 EXPORT_SYMBOL_GPL(percpu_ida_destroy);
274
275 /**
276 * percpu_ida_init - initialize a percpu tag pool
277 * @pool: pool to initialize
278 * @nr_tags: number of tags that will be available for allocation
279 *
280 * Initializes @pool so that it can be used to allocate tags - integers in the
281 * range [0, nr_tags). Typically, they'll be used by driver code to refer to a
282 * preallocated array of tag structures.
283 *
284 * Allocation is percpu, but sharding is limited by nr_tags - for best
285 * performance, the workload should not span more cpus than nr_tags / 128.
286 */
__percpu_ida_init(struct percpu_ida * pool,unsigned long nr_tags,unsigned long max_size,unsigned long batch_size)287 int __percpu_ida_init(struct percpu_ida *pool, unsigned long nr_tags,
288 unsigned long max_size, unsigned long batch_size)
289 {
290 unsigned i, cpu, order;
291
292 memset(pool, 0, sizeof(*pool));
293
294 init_waitqueue_head(&pool->wait);
295 spin_lock_init(&pool->lock);
296 pool->nr_tags = nr_tags;
297 pool->percpu_max_size = max_size;
298 pool->percpu_batch_size = batch_size;
299
300 /* Guard against overflow */
301 if (nr_tags > (unsigned) INT_MAX + 1) {
302 pr_err("percpu_ida_init(): nr_tags too large\n");
303 return -EINVAL;
304 }
305
306 order = get_order(nr_tags * sizeof(unsigned));
307 pool->freelist = (void *) __get_free_pages(GFP_KERNEL, order);
308 if (!pool->freelist)
309 return -ENOMEM;
310
311 for (i = 0; i < nr_tags; i++)
312 pool->freelist[i] = i;
313
314 pool->nr_free = nr_tags;
315
316 pool->tag_cpu = __alloc_percpu(sizeof(struct percpu_ida_cpu) +
317 pool->percpu_max_size * sizeof(unsigned),
318 sizeof(unsigned));
319 if (!pool->tag_cpu)
320 goto err;
321
322 for_each_possible_cpu(cpu)
323 spin_lock_init(&per_cpu_ptr(pool->tag_cpu, cpu)->lock);
324
325 return 0;
326 err:
327 percpu_ida_destroy(pool);
328 return -ENOMEM;
329 }
330 EXPORT_SYMBOL_GPL(__percpu_ida_init);
331
332 /**
333 * percpu_ida_for_each_free - iterate free ids of a pool
334 * @pool: pool to iterate
335 * @fn: interate callback function
336 * @data: parameter for @fn
337 *
338 * Note, this doesn't guarantee to iterate all free ids restrictly. Some free
339 * ids might be missed, some might be iterated duplicated, and some might
340 * be iterated and not free soon.
341 */
percpu_ida_for_each_free(struct percpu_ida * pool,percpu_ida_cb fn,void * data)342 int percpu_ida_for_each_free(struct percpu_ida *pool, percpu_ida_cb fn,
343 void *data)
344 {
345 unsigned long flags;
346 struct percpu_ida_cpu *remote;
347 unsigned cpu, i, err = 0;
348
349 local_irq_save(flags);
350 for_each_possible_cpu(cpu) {
351 remote = per_cpu_ptr(pool->tag_cpu, cpu);
352 spin_lock(&remote->lock);
353 for (i = 0; i < remote->nr_free; i++) {
354 err = fn(remote->freelist[i], data);
355 if (err)
356 break;
357 }
358 spin_unlock(&remote->lock);
359 if (err)
360 goto out;
361 }
362
363 spin_lock(&pool->lock);
364 for (i = 0; i < pool->nr_free; i++) {
365 err = fn(pool->freelist[i], data);
366 if (err)
367 break;
368 }
369 spin_unlock(&pool->lock);
370 out:
371 local_irq_restore(flags);
372 return err;
373 }
374 EXPORT_SYMBOL_GPL(percpu_ida_for_each_free);
375
376 /**
377 * percpu_ida_free_tags - return free tags number of a specific cpu or global pool
378 * @pool: pool related
379 * @cpu: specific cpu or global pool if @cpu == nr_cpu_ids
380 *
381 * Note: this just returns a snapshot of free tags number.
382 */
percpu_ida_free_tags(struct percpu_ida * pool,int cpu)383 unsigned percpu_ida_free_tags(struct percpu_ida *pool, int cpu)
384 {
385 struct percpu_ida_cpu *remote;
386 if (cpu == nr_cpu_ids)
387 return pool->nr_free;
388 remote = per_cpu_ptr(pool->tag_cpu, cpu);
389 return remote->nr_free;
390 }
391 EXPORT_SYMBOL_GPL(percpu_ida_free_tags);
392