1/*
  2 * Copyright (C) 2016 Facebook
  3 * Copyright (C) 2013-2014 Jens Axboe
  4 *
  5 * This program is free software; you can redistribute it and/or
  6 * modify it under the terms of the GNU General Public
  7 * License v2 as published by the Free Software Foundation.
  8 *
  9 * This program is distributed in the hope that it will be useful,
 10 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 11 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 12 * General Public License for more details.
 13 *
 14 * You should have received a copy of the GNU General Public License
 15 * along with this program.  If not, see <https://www.gnu.org/licenses/>.
 16 */
 17
 18#include <linux/random.h>
 19#include <linux/sbitmap.h>
 20
 21int sbitmap_init_node(struct sbitmap *sb, unsigned int depth, int shift,
 22		      gfp_t flags, int node)
 23{
 24	unsigned int bits_per_word;
 25	unsigned int i;
 26
 27	if (shift < 0) {
 28		shift = ilog2(BITS_PER_LONG);
 29		/*
 30		 * If the bitmap is small, shrink the number of bits per word so
 31		 * we spread over a few cachelines, at least. If less than 4
 32		 * bits, just forget about it, it's not going to work optimally
 33		 * anyway.
 34		 */
 35		if (depth >= 4) {
 36			while ((4U << shift) > depth)
 37				shift--;
 38		}
 39	}
 40	bits_per_word = 1U << shift;
 41	if (bits_per_word > BITS_PER_LONG)
 42		return -EINVAL;
 43
 44	sb->shift = shift;
 45	sb->depth = depth;
 46	sb->map_nr = DIV_ROUND_UP(sb->depth, bits_per_word);
 47
 48	if (depth == 0) {
 49		sb->map = NULL;
 50		return 0;
 51	}
 52
 53	sb->map = kzalloc_node(sb->map_nr * sizeof(*sb->map), flags, node);
 54	if (!sb->map)
 55		return -ENOMEM;
 56
 57	for (i = 0; i < sb->map_nr; i++) {
 58		sb->map[i].depth = min(depth, bits_per_word);
 59		depth -= sb->map[i].depth;
 60	}
 61	return 0;
 62}
 63EXPORT_SYMBOL_GPL(sbitmap_init_node);
 64
 65void sbitmap_resize(struct sbitmap *sb, unsigned int depth)
 66{
 67	unsigned int bits_per_word = 1U << sb->shift;
 68	unsigned int i;
 69
 70	sb->depth = depth;
 71	sb->map_nr = DIV_ROUND_UP(sb->depth, bits_per_word);
 72
 73	for (i = 0; i < sb->map_nr; i++) {
 74		sb->map[i].depth = min(depth, bits_per_word);
 75		depth -= sb->map[i].depth;
 76	}
 77}
 78EXPORT_SYMBOL_GPL(sbitmap_resize);
 79
 80static int __sbitmap_get_word(struct sbitmap_word *word, unsigned int hint,
 81			      bool wrap)
 82{
 83	unsigned int orig_hint = hint;
 84	int nr;
 85
 86	while (1) {
 87		nr = find_next_zero_bit(&word->word, word->depth, hint);
 88		if (unlikely(nr >= word->depth)) {
 89			/*
 90			 * We started with an offset, and we didn't reset the
 91			 * offset to 0 in a failure case, so start from 0 to
 92			 * exhaust the map.
 93			 */
 94			if (orig_hint && hint && wrap) {
 95				hint = orig_hint = 0;
 96				continue;
 97			}
 98			return -1;
 99		}
100
101		if (!test_and_set_bit(nr, &word->word))
102			break;
103
104		hint = nr + 1;
105		if (hint >= word->depth - 1)
106			hint = 0;
107	}
108
109	return nr;
110}
111
112int sbitmap_get(struct sbitmap *sb, unsigned int alloc_hint, bool round_robin)
113{
114	unsigned int i, index;
115	int nr = -1;
116
117	index = SB_NR_TO_INDEX(sb, alloc_hint);
118
119	for (i = 0; i < sb->map_nr; i++) {
120		nr = __sbitmap_get_word(&sb->map[index],
121					SB_NR_TO_BIT(sb, alloc_hint),
122					!round_robin);
123		if (nr != -1) {
124			nr += index << sb->shift;
125			break;
126		}
127
128		/* Jump to next index. */
129		index++;
130		alloc_hint = index << sb->shift;
131
132		if (index >= sb->map_nr) {
133			index = 0;
134			alloc_hint = 0;
135		}
136	}
137
138	return nr;
139}
140EXPORT_SYMBOL_GPL(sbitmap_get);
141
142bool sbitmap_any_bit_set(const struct sbitmap *sb)
143{
144	unsigned int i;
145
146	for (i = 0; i < sb->map_nr; i++) {
147		if (sb->map[i].word)
148			return true;
149	}
150	return false;
151}
152EXPORT_SYMBOL_GPL(sbitmap_any_bit_set);
153
154bool sbitmap_any_bit_clear(const struct sbitmap *sb)
155{
156	unsigned int i;
157
158	for (i = 0; i < sb->map_nr; i++) {
159		const struct sbitmap_word *word = &sb->map[i];
160		unsigned long ret;
161
162		ret = find_first_zero_bit(&word->word, word->depth);
163		if (ret < word->depth)
164			return true;
165	}
166	return false;
167}
168EXPORT_SYMBOL_GPL(sbitmap_any_bit_clear);
169
170unsigned int sbitmap_weight(const struct sbitmap *sb)
171{
172	unsigned int i, weight = 0;
173
174	for (i = 0; i < sb->map_nr; i++) {
175		const struct sbitmap_word *word = &sb->map[i];
176
177		weight += bitmap_weight(&word->word, word->depth);
178	}
179	return weight;
180}
181EXPORT_SYMBOL_GPL(sbitmap_weight);
182
183static unsigned int sbq_calc_wake_batch(unsigned int depth)
184{
185	unsigned int wake_batch;
186
187	/*
188	 * For each batch, we wake up one queue. We need to make sure that our
189	 * batch size is small enough that the full depth of the bitmap is
190	 * enough to wake up all of the queues.
191	 */
192	wake_batch = SBQ_WAKE_BATCH;
193	if (wake_batch > depth / SBQ_WAIT_QUEUES)
194		wake_batch = max(1U, depth / SBQ_WAIT_QUEUES);
195
196	return wake_batch;
197}
198
199int sbitmap_queue_init_node(struct sbitmap_queue *sbq, unsigned int depth,
200			    int shift, bool round_robin, gfp_t flags, int node)
201{
202	int ret;
203	int i;
204
205	ret = sbitmap_init_node(&sbq->sb, depth, shift, flags, node);
206	if (ret)
207		return ret;
208
209	sbq->alloc_hint = alloc_percpu_gfp(unsigned int, flags);
210	if (!sbq->alloc_hint) {
211		sbitmap_free(&sbq->sb);
212		return -ENOMEM;
213	}
214
215	if (depth && !round_robin) {
216		for_each_possible_cpu(i)
217			*per_cpu_ptr(sbq->alloc_hint, i) = prandom_u32() % depth;
218	}
219
220	sbq->wake_batch = sbq_calc_wake_batch(depth);
221	atomic_set(&sbq->wake_index, 0);
222
223	sbq->ws = kzalloc_node(SBQ_WAIT_QUEUES * sizeof(*sbq->ws), flags, node);
224	if (!sbq->ws) {
225		free_percpu(sbq->alloc_hint);
226		sbitmap_free(&sbq->sb);
227		return -ENOMEM;
228	}
229
230	for (i = 0; i < SBQ_WAIT_QUEUES; i++) {
231		init_waitqueue_head(&sbq->ws[i].wait);
232		atomic_set(&sbq->ws[i].wait_cnt, sbq->wake_batch);
233	}
234
235	sbq->round_robin = round_robin;
236	return 0;
237}
238EXPORT_SYMBOL_GPL(sbitmap_queue_init_node);
239
240void sbitmap_queue_resize(struct sbitmap_queue *sbq, unsigned int depth)
241{
242	sbq->wake_batch = sbq_calc_wake_batch(depth);
243	sbitmap_resize(&sbq->sb, depth);
244}
245EXPORT_SYMBOL_GPL(sbitmap_queue_resize);
246
247int __sbitmap_queue_get(struct sbitmap_queue *sbq)
248{
249	unsigned int hint, depth;
250	int nr;
251
252	hint = this_cpu_read(*sbq->alloc_hint);
253	depth = READ_ONCE(sbq->sb.depth);
254	if (unlikely(hint >= depth)) {
255		hint = depth ? prandom_u32() % depth : 0;
256		this_cpu_write(*sbq->alloc_hint, hint);
257	}
258	nr = sbitmap_get(&sbq->sb, hint, sbq->round_robin);
259
260	if (nr == -1) {
261		/* If the map is full, a hint won't do us much good. */
262		this_cpu_write(*sbq->alloc_hint, 0);
263	} else if (nr == hint || unlikely(sbq->round_robin)) {
264		/* Only update the hint if we used it. */
265		hint = nr + 1;
266		if (hint >= depth - 1)
267			hint = 0;
268		this_cpu_write(*sbq->alloc_hint, hint);
269	}
270
271	return nr;
272}
273EXPORT_SYMBOL_GPL(__sbitmap_queue_get);
274
275static struct sbq_wait_state *sbq_wake_ptr(struct sbitmap_queue *sbq)
276{
277	int i, wake_index;
278
279	wake_index = atomic_read(&sbq->wake_index);
280	for (i = 0; i < SBQ_WAIT_QUEUES; i++) {
281		struct sbq_wait_state *ws = &sbq->ws[wake_index];
282
283		if (waitqueue_active(&ws->wait)) {
284			int o = atomic_read(&sbq->wake_index);
285
286			if (wake_index != o)
287				atomic_cmpxchg(&sbq->wake_index, o, wake_index);
288			return ws;
289		}
290
291		wake_index = sbq_index_inc(wake_index);
292	}
293
294	return NULL;
295}
296
297static void sbq_wake_up(struct sbitmap_queue *sbq)
298{
299	struct sbq_wait_state *ws;
300	int wait_cnt;
301
302	/* Ensure that the wait list checks occur after clear_bit(). */
303	smp_mb();
304
305	ws = sbq_wake_ptr(sbq);
306	if (!ws)
307		return;
308
309	wait_cnt = atomic_dec_return(&ws->wait_cnt);
310	if (unlikely(wait_cnt < 0))
311		wait_cnt = atomic_inc_return(&ws->wait_cnt);
312	if (wait_cnt == 0) {
313		atomic_add(sbq->wake_batch, &ws->wait_cnt);
314		sbq_index_atomic_inc(&sbq->wake_index);
315		wake_up(&ws->wait);
316	}
317}
318
319void sbitmap_queue_clear(struct sbitmap_queue *sbq, unsigned int nr,
320			 unsigned int cpu)
321{
322	sbitmap_clear_bit(&sbq->sb, nr);
323	sbq_wake_up(sbq);
324	if (likely(!sbq->round_robin && nr < sbq->sb.depth))
325		*per_cpu_ptr(sbq->alloc_hint, cpu) = nr;
326}
327EXPORT_SYMBOL_GPL(sbitmap_queue_clear);
328
329void sbitmap_queue_wake_all(struct sbitmap_queue *sbq)
330{
331	int i, wake_index;
332
333	/*
334	 * Make sure all changes prior to this are visible from other CPUs.
335	 */
336	smp_mb();
337	wake_index = atomic_read(&sbq->wake_index);
338	for (i = 0; i < SBQ_WAIT_QUEUES; i++) {
339		struct sbq_wait_state *ws = &sbq->ws[wake_index];
340
341		if (waitqueue_active(&ws->wait))
342			wake_up(&ws->wait);
343
344		wake_index = sbq_index_inc(wake_index);
345	}
346}
347EXPORT_SYMBOL_GPL(sbitmap_queue_wake_all);