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
30struct 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
42static 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 */
60static 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 */
106static 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
114static 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_WAIT 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 */
144int 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}
207EXPORT_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 */
216void 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}
258EXPORT_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 */
266void 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}
272EXPORT_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 */
286int __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;
325err:
326	percpu_ida_destroy(pool);
327	return -ENOMEM;
328}
329EXPORT_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 */
341int 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);
369out:
370	local_irq_restore(flags);
371	return err;
372}
373EXPORT_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 */
382unsigned 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}
390EXPORT_SYMBOL_GPL(percpu_ida_free_tags);
391