blk-mq: abstract tag allocation out into sbitmap library

This is a generally useful data structure, so make it available to
anyone else who might want to use it. It's also a nice cleanup
separating the allocation logic from the rest of the tag handling logic.

The code is behind a new Kconfig option, CONFIG_SBITMAP, which is only
selected by CONFIG_BLOCK for now.

This should be a complete noop functionality-wise.

Signed-off-by: Omar Sandoval <osandov@fb.com>
Signed-off-by: Jens Axboe <axboe@fb.com>

1 files changed, 301 insertions, 0 deletions

diff --git a/lib/sbitmap.c b/lib/sbitmap.c
new file mode 100644
index 000000000000..dfc084ac6937
--- /dev/null
+++ b/lib/sbitmap.c
@@ -0,0 +1,301 @@
+/*
+ * Copyright (C) 2016 Facebook
+ * Copyright (C) 2013-2014 Jens Axboe
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public
+ * License v2 as published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+#include <linux/sbitmap.h>
+
+int sbitmap_init_node(struct sbitmap *sb, unsigned int depth, int shift,
+                      gfp_t flags, int node)
+{
+        unsigned int bits_per_word;
+        unsigned int i;
+
+        if (shift < 0) {
+                shift = ilog2(BITS_PER_LONG);
+                /*
+                 * If the bitmap is small, shrink the number of bits per word so
+                 * we spread over a few cachelines, at least. If less than 4
+                 * bits, just forget about it, it's not going to work optimally
+                 * anyway.
+                 */
+                if (depth >= 4) {
+                        while ((4U << shift) > depth)
+                                shift--;
+                }
+        }
+        bits_per_word = 1U << shift;
+        if (bits_per_word > BITS_PER_LONG)
+                return -EINVAL;
+
+        sb->shift = shift;
+        sb->depth = depth;
+        sb->map_nr = DIV_ROUND_UP(sb->depth, bits_per_word);
+
+        if (depth == 0) {
+                sb->map = NULL;
+                return 0;
+        }
+
+        sb->map = kzalloc_node(sb->map_nr * sizeof(*sb->map), flags, node);
+        if (!sb->map)
+                return -ENOMEM;
+
+        for (i = 0; i < sb->map_nr; i++) {
+                sb->map[i].depth = min(depth, bits_per_word);
+                depth -= sb->map[i].depth;
+        }
+        return 0;
+}
+EXPORT_SYMBOL_GPL(sbitmap_init_node);
+
+void sbitmap_resize(struct sbitmap *sb, unsigned int depth)
+{
+        unsigned int bits_per_word = 1U << sb->shift;
+        unsigned int i;
+
+        sb->depth = depth;
+        sb->map_nr = DIV_ROUND_UP(sb->depth, bits_per_word);
+
+        for (i = 0; i < sb->map_nr; i++) {
+                sb->map[i].depth = min(depth, bits_per_word);
+                depth -= sb->map[i].depth;
+        }
+}
+EXPORT_SYMBOL_GPL(sbitmap_resize);
+
+static int __sbitmap_get_word(struct sbitmap_word *word, unsigned int hint,
+                              bool wrap)
+{
+        unsigned int orig_hint = hint;
+        int nr;
+
+        while (1) {
+                nr = find_next_zero_bit(&word->word, word->depth, hint);
+                if (unlikely(nr >= word->depth)) {
+                        /*
+                         * We started with an offset, and we didn't reset the
+                         * offset to 0 in a failure case, so start from 0 to
+                         * exhaust the map.
+                         */
+                        if (orig_hint && hint && wrap) {
+                                hint = orig_hint = 0;
+                                continue;
+                        }
+                        return -1;
+                }
+
+                if (!test_and_set_bit(nr, &word->word))
+                        break;
+
+                hint = nr + 1;
+                if (hint >= word->depth - 1)
+                        hint = 0;
+        }
+
+        return nr;
+}
+
+int sbitmap_get(struct sbitmap *sb, unsigned int alloc_hint, bool round_robin)
+{
+        unsigned int i, index;
+        int nr = -1;
+
+        index = SB_NR_TO_INDEX(sb, alloc_hint);
+
+        for (i = 0; i < sb->map_nr; i++) {
+                nr = __sbitmap_get_word(&sb->map[index],
+                                        SB_NR_TO_BIT(sb, alloc_hint),
+                                        !round_robin);
+                if (nr != -1) {
+                        nr += index << sb->shift;
+                        break;
+                }
+
+                /* Jump to next index. */
+                index++;
+                alloc_hint = index << sb->shift;
+
+                if (index >= sb->map_nr) {
+                        index = 0;
+                        alloc_hint = 0;
+                }
+        }
+
+        return nr;
+}
+EXPORT_SYMBOL_GPL(sbitmap_get);
+
+bool sbitmap_any_bit_set(const struct sbitmap *sb)
+{
+        unsigned int i;
+
+        for (i = 0; i < sb->map_nr; i++) {
+                if (sb->map[i].word)
+                        return true;
+        }
+        return false;
+}
+EXPORT_SYMBOL_GPL(sbitmap_any_bit_set);
+
+bool sbitmap_any_bit_clear(const struct sbitmap *sb)
+{
+        unsigned int i;
+
+        for (i = 0; i < sb->map_nr; i++) {
+                const struct sbitmap_word *word = &sb->map[i];
+                unsigned long ret;
+
+                ret = find_first_zero_bit(&word->word, word->depth);
+                if (ret < word->depth)
+                        return true;
+        }
+        return false;
+}
+EXPORT_SYMBOL_GPL(sbitmap_any_bit_clear);
+
+unsigned int sbitmap_weight(const struct sbitmap *sb)
+{
+        unsigned int i, weight;
+
+        for (i = 0; i < sb->map_nr; i++) {
+                const struct sbitmap_word *word = &sb->map[i];
+
+                weight += bitmap_weight(&word->word, word->depth);
+        }
+        return weight;
+}
+EXPORT_SYMBOL_GPL(sbitmap_weight);
+
+static unsigned int sbq_calc_wake_batch(unsigned int depth)
+{
+        unsigned int wake_batch;
+
+        /*
+         * For each batch, we wake up one queue. We need to make sure that our
+         * batch size is small enough that the full depth of the bitmap is
+         * enough to wake up all of the queues.
+         */
+        wake_batch = SBQ_WAKE_BATCH;
+        if (wake_batch > depth / SBQ_WAIT_QUEUES)
+                wake_batch = max(1U, depth / SBQ_WAIT_QUEUES);
+
+        return wake_batch;
+}
+
+int sbitmap_queue_init_node(struct sbitmap_queue *sbq, unsigned int depth,
+                            int shift, gfp_t flags, int node)
+{
+        int ret;
+        int i;
+
+        ret = sbitmap_init_node(&sbq->sb, depth, shift, flags, node);
+        if (ret)
+                return ret;
+
+        sbq->wake_batch = sbq_calc_wake_batch(depth);
+        atomic_set(&sbq->wake_index, 0);
+
+        sbq->ws = kzalloc(SBQ_WAIT_QUEUES * sizeof(*sbq->ws), flags);
+        if (!sbq->ws) {
+                sbitmap_free(&sbq->sb);
+                return -ENOMEM;
+        }
+
+        for (i = 0; i < SBQ_WAIT_QUEUES; i++) {
+                init_waitqueue_head(&sbq->ws[i].wait);
+                atomic_set(&sbq->ws[i].wait_cnt, sbq->wake_batch);
+        }
+        return 0;
+}
+EXPORT_SYMBOL_GPL(sbitmap_queue_init_node);
+
+void sbitmap_queue_resize(struct sbitmap_queue *sbq, unsigned int depth)
+{
+        sbq->wake_batch = sbq_calc_wake_batch(depth);
+        sbitmap_resize(&sbq->sb, depth);
+}
+EXPORT_SYMBOL_GPL(sbitmap_queue_resize);
+
+static struct sbq_wait_state *sbq_wake_ptr(struct sbitmap_queue *sbq)
+{
+        int i, wake_index;
+
+        wake_index = atomic_read(&sbq->wake_index);
+        for (i = 0; i < SBQ_WAIT_QUEUES; i++) {
+                struct sbq_wait_state *ws = &sbq->ws[wake_index];
+
+                if (waitqueue_active(&ws->wait)) {
+                        int o = atomic_read(&sbq->wake_index);
+
+                        if (wake_index != o)
+                                atomic_cmpxchg(&sbq->wake_index, o, wake_index);
+                        return ws;
+                }
+
+                wake_index = sbq_index_inc(wake_index);
+        }
+
+        return NULL;
+}
+
+static void sbq_wake_up(struct sbitmap_queue *sbq)
+{
+        struct sbq_wait_state *ws;
+        int wait_cnt;
+
+        /* Ensure that the wait list checks occur after clear_bit(). */
+        smp_mb();
+
+        ws = sbq_wake_ptr(sbq);
+        if (!ws)
+                return;
+
+        wait_cnt = atomic_dec_return(&ws->wait_cnt);
+        if (unlikely(wait_cnt < 0))
+                wait_cnt = atomic_inc_return(&ws->wait_cnt);
+        if (wait_cnt == 0) {
+                atomic_add(sbq->wake_batch, &ws->wait_cnt);
+                sbq_index_atomic_inc(&sbq->wake_index);
+                wake_up(&ws->wait);
+        }
+}
+
+void sbitmap_queue_clear(struct sbitmap_queue *sbq, unsigned int nr)
+{
+        sbitmap_clear_bit(&sbq->sb, nr);
+        sbq_wake_up(sbq);
+}
+EXPORT_SYMBOL_GPL(sbitmap_queue_clear);
+
+void sbitmap_queue_wake_all(struct sbitmap_queue *sbq)
+{
+        int i, wake_index;
+
+        /*
+         * Make sure all changes prior to this are visible from other CPUs.
+         */
+        smp_mb();
+        wake_index = atomic_read(&sbq->wake_index);
+        for (i = 0; i < SBQ_WAIT_QUEUES; i++) {
+                struct sbq_wait_state *ws = &sbq->ws[wake_index];
+
+                if (waitqueue_active(&ws->wait))
+                        wake_up(&ws->wait);
+
+                wake_index = sbq_index_inc(wake_index);
+        }
+}
+EXPORT_SYMBOL_GPL(sbitmap_queue_wake_all);