1 files changed, 504 insertions, 234 deletions

diff --git a/lib/sbitmap.c b/lib/sbitmap.c
index 80aa8d5463fa..4d188d05db15 100644
--- a/lib/sbitmap.c
+++ b/lib/sbitmap.c
@@ -1,18 +1,7 @@
+// SPDX-License-Identifier: GPL-2.0-only
 /*
  * 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/sched.h>
@@ -20,25 +9,105 @@
 #include <linux/sbitmap.h>
 #include <linux/seq_file.h>
 
-int sbitmap_init_node(struct sbitmap *sb, unsigned int depth, int shift,
-		      gfp_t flags, int node)
+static int init_alloc_hint(struct sbitmap *sb, gfp_t flags)
 {
-	unsigned int bits_per_word;
-	unsigned int i;
+	unsigned depth = sb->depth;
+
+	sb->alloc_hint = alloc_percpu_gfp(unsigned int, flags);
+	if (!sb->alloc_hint)
+		return -ENOMEM;
+
+	if (depth && !sb->round_robin) {
+		int i;
+
+		for_each_possible_cpu(i)
+			*per_cpu_ptr(sb->alloc_hint, i) = get_random_u32_below(depth);
+	}
+	return 0;
+}
+
+static inline unsigned update_alloc_hint_before_get(struct sbitmap *sb,
+						    unsigned int depth)
+{
+	unsigned hint;
+
+	hint = this_cpu_read(*sb->alloc_hint);
+	if (unlikely(hint >= depth)) {
+		hint = depth ? get_random_u32_below(depth) : 0;
+		this_cpu_write(*sb->alloc_hint, hint);
+	}
 
-	if (shift < 0) {
-		shift = ilog2(BITS_PER_LONG);
+	return hint;
+}
+
+static inline void update_alloc_hint_after_get(struct sbitmap *sb,
+					       unsigned int depth,
+					       unsigned int hint,
+					       unsigned int nr)
+{
+	if (nr == -1) {
+		/* If the map is full, a hint won't do us much good. */
+		this_cpu_write(*sb->alloc_hint, 0);
+	} else if (nr == hint || unlikely(sb->round_robin)) {
+		/* Only update the hint if we used it. */
+		hint = nr + 1;
+		if (hint >= depth - 1)
+			hint = 0;
+		this_cpu_write(*sb->alloc_hint, hint);
+	}
+}
+
+/*
+ * See if we have deferred clears that we can batch move
+ */
+static inline bool sbitmap_deferred_clear(struct sbitmap_word *map,
+		unsigned int depth, unsigned int alloc_hint, bool wrap)
+{
+	unsigned long mask, word_mask;
+
+	guard(raw_spinlock_irqsave)(&map->swap_lock);
+
+	if (!map->cleared) {
+		if (depth == 0)
+			return false;
+
+		word_mask = (~0UL) >> (BITS_PER_LONG - depth);
 		/*
-		 * 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.
+		 * The current behavior is to always retry after moving
+		 * ->cleared to word, and we change it to retry in case
+		 * of any free bits. To avoid an infinite loop, we need
+		 * to take wrap & alloc_hint into account, otherwise a
+		 * soft lockup may occur.
 		 */
-		if (depth >= 4) {
-			while ((4U << shift) > depth)
-				shift--;
-		}
+		if (!wrap && alloc_hint)
+			word_mask &= ~((1UL << alloc_hint) - 1);
+
+		return (READ_ONCE(map->word) & word_mask) != word_mask;
 	}
+
+	/*
+	 * First get a stable cleared mask, setting the old mask to 0.
+	 */
+	mask = xchg(&map->cleared, 0);
+
+	/*
+	 * Now clear the masked bits in our free word
+	 */
+	atomic_long_andnot(mask, (atomic_long_t *)&map->word);
+	BUILD_BUG_ON(sizeof(atomic_long_t) != sizeof(map->word));
+	return true;
+}
+
+int sbitmap_init_node(struct sbitmap *sb, unsigned int depth, int shift,
+		      gfp_t flags, int node, bool round_robin,
+		      bool alloc_hint)
+{
+	unsigned int bits_per_word;
+	int i;
+
+	if (shift < 0)
+		shift = sbitmap_calculate_shift(depth);
+
 	bits_per_word = 1U << shift;
 	if (bits_per_word > BITS_PER_LONG)
 		return -EINVAL;
@@ -46,20 +115,29 @@ int sbitmap_init_node(struct sbitmap *sb, unsigned int depth, int shift,
 	sb->shift = shift;
 	sb->depth = depth;
 	sb->map_nr = DIV_ROUND_UP(sb->depth, bits_per_word);
+	sb->round_robin = round_robin;
 
 	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;
+	if (alloc_hint) {
+		if (init_alloc_hint(sb, flags))
+			return -ENOMEM;
+	} else {
+		sb->alloc_hint = NULL;
+	}
 
-	for (i = 0; i < sb->map_nr; i++) {
-		sb->map[i].depth = min(depth, bits_per_word);
-		depth -= sb->map[i].depth;
+	sb->map = kvzalloc_node(sb->map_nr * sizeof(*sb->map), flags, node);
+	if (!sb->map) {
+		free_percpu(sb->alloc_hint);
+		return -ENOMEM;
 	}
+
+	for (i = 0; i < sb->map_nr; i++)
+		raw_spin_lock_init(&sb->map[i].swap_lock);
+
 	return 0;
 }
 EXPORT_SYMBOL_GPL(sbitmap_init_node);
@@ -69,22 +147,22 @@ void sbitmap_resize(struct sbitmap *sb, unsigned int depth)
 	unsigned int bits_per_word = 1U << sb->shift;
 	unsigned int i;
 
+	for (i = 0; i < sb->map_nr; i++)
+		sbitmap_deferred_clear(&sb->map[i], 0, 0, 0);
+
 	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(unsigned long *word, unsigned long depth,
 			      unsigned int hint, bool wrap)
 {
-	unsigned int orig_hint = hint;
 	int nr;
 
+	/* don't wrap if starting from 0 */
+	wrap = wrap && hint;
+
 	while (1) {
 		nr = find_next_zero_bit(word, depth, hint);
 		if (unlikely(nr >= depth)) {
@@ -93,14 +171,14 @@ static int __sbitmap_get_word(unsigned long *word, unsigned long depth,
 			 * offset to 0 in a failure case, so start from 0 to
 			 * exhaust the map.
 			 */
-			if (orig_hint && hint && wrap) {
-				hint = orig_hint = 0;
+			if (hint && wrap) {
+				hint = 0;
 				continue;
 			}
 			return -1;
 		}
 
-		if (!test_and_set_bit(nr, word))
+		if (!test_and_set_bit_lock(nr, word))
 			break;
 
 		hint = nr + 1;
@@ -111,106 +189,191 @@ static int __sbitmap_get_word(unsigned long *word, unsigned long depth,
 	return nr;
 }
 
-int sbitmap_get(struct sbitmap *sb, unsigned int alloc_hint, bool round_robin)
+static int sbitmap_find_bit_in_word(struct sbitmap_word *map,
+				    unsigned int depth,
+				    unsigned int alloc_hint,
+				    bool wrap)
 {
-	unsigned int i, index;
-	int nr = -1;
+	int nr;
 
-	index = SB_NR_TO_INDEX(sb, alloc_hint);
+	do {
+		nr = __sbitmap_get_word(&map->word, depth,
+					alloc_hint, wrap);
+		if (nr != -1)
+			break;
+		if (!sbitmap_deferred_clear(map, depth, alloc_hint, wrap))
+			break;
+	} while (1);
+
+	return nr;
+}
+
+static unsigned int __map_depth_with_shallow(const struct sbitmap *sb,
+					     int index,
+					     unsigned int shallow_depth)
+{
+	u64 shallow_word_depth;
+	unsigned int word_depth, reminder;
+
+	word_depth = __map_depth(sb, index);
+	if (shallow_depth >= sb->depth)
+		return word_depth;
+
+	shallow_word_depth = word_depth * shallow_depth;
+	reminder = do_div(shallow_word_depth, sb->depth);
+
+	if (reminder >= (index + 1) * word_depth)
+		shallow_word_depth++;
+
+	return (unsigned int)shallow_word_depth;
+}
+
+static int sbitmap_find_bit(struct sbitmap *sb,
+			    unsigned int shallow_depth,
+			    unsigned int index,
+			    unsigned int alloc_hint,
+			    bool wrap)
+{
+	unsigned int i;
+	int nr = -1;
 
 	for (i = 0; i < sb->map_nr; i++) {
-		nr = __sbitmap_get_word(&sb->map[index].word,
-					sb->map[index].depth,
-					SB_NR_TO_BIT(sb, alloc_hint),
-					!round_robin);
+		unsigned int depth = __map_depth_with_shallow(sb, index,
+							      shallow_depth);
+
+		if (depth)
+			nr = sbitmap_find_bit_in_word(&sb->map[index], depth,
+						      alloc_hint, wrap);
 		if (nr != -1) {
 			nr += index << sb->shift;
 			break;
 		}
 
 		/* Jump to next index. */
-		index++;
-		alloc_hint = index << sb->shift;
-
-		if (index >= sb->map_nr) {
+		alloc_hint = 0;
+		if (++index >= sb->map_nr)
 			index = 0;
-			alloc_hint = 0;
-		}
 	}
 
 	return nr;
 }
+
+static int __sbitmap_get(struct sbitmap *sb, unsigned int alloc_hint)
+{
+	unsigned int index;
+
+	index = SB_NR_TO_INDEX(sb, alloc_hint);
+
+	/*
+	 * Unless we're doing round robin tag allocation, just use the
+	 * alloc_hint to find the right word index. No point in looping
+	 * twice in find_next_zero_bit() for that case.
+	 */
+	if (sb->round_robin)
+		alloc_hint = SB_NR_TO_BIT(sb, alloc_hint);
+	else
+		alloc_hint = 0;
+
+	return sbitmap_find_bit(sb, UINT_MAX, index, alloc_hint,
+				!sb->round_robin);
+}
+
+int sbitmap_get(struct sbitmap *sb)
+{
+	int nr;
+	unsigned int hint, depth;
+
+	if (WARN_ON_ONCE(unlikely(!sb->alloc_hint)))
+		return -1;
+
+	depth = READ_ONCE(sb->depth);
+	hint = update_alloc_hint_before_get(sb, depth);
+	nr = __sbitmap_get(sb, hint);
+	update_alloc_hint_after_get(sb, depth, hint, nr);
+
+	return nr;
+}
 EXPORT_SYMBOL_GPL(sbitmap_get);
 
-int sbitmap_get_shallow(struct sbitmap *sb, unsigned int alloc_hint,
-			unsigned long shallow_depth)
+static int __sbitmap_get_shallow(struct sbitmap *sb,
+				 unsigned int alloc_hint,
+				 unsigned long shallow_depth)
 {
-	unsigned int i, index;
-	int nr = -1;
+	unsigned int index;
 
 	index = SB_NR_TO_INDEX(sb, alloc_hint);
+	alloc_hint = SB_NR_TO_BIT(sb, alloc_hint);
 
-	for (i = 0; i < sb->map_nr; i++) {
-		nr = __sbitmap_get_word(&sb->map[index].word,
-					min(sb->map[index].depth, shallow_depth),
-					SB_NR_TO_BIT(sb, alloc_hint), true);
-		if (nr != -1) {
-			nr += index << sb->shift;
-			break;
-		}
+	return sbitmap_find_bit(sb, shallow_depth, index, alloc_hint, true);
+}
 
-		/* Jump to next index. */
-		index++;
-		alloc_hint = index << sb->shift;
+/**
+ * sbitmap_get_shallow() - Try to allocate a free bit from a &struct sbitmap,
+ * limiting the depth used from each word.
+ * @sb: Bitmap to allocate from.
+ * @shallow_depth: The maximum number of bits to allocate from the bitmap.
+ *
+ * This rather specific operation allows for having multiple users with
+ * different allocation limits. E.g., there can be a high-priority class that
+ * uses sbitmap_get() and a low-priority class that uses sbitmap_get_shallow()
+ * with a @shallow_depth of (sb->depth >> 1). Then, the low-priority
+ * class can only allocate half of the total bits in the bitmap, preventing it
+ * from starving out the high-priority class.
+ *
+ * Return: Non-negative allocated bit number if successful, -1 otherwise.
+ */
+static int sbitmap_get_shallow(struct sbitmap *sb, unsigned long shallow_depth)
+{
+	int nr;
+	unsigned int hint, depth;
 
-		if (index >= sb->map_nr) {
-			index = 0;
-			alloc_hint = 0;
-		}
-	}
+	if (WARN_ON_ONCE(unlikely(!sb->alloc_hint)))
+		return -1;
+
+	depth = READ_ONCE(sb->depth);
+	hint = update_alloc_hint_before_get(sb, depth);
+	nr = __sbitmap_get_shallow(sb, hint, shallow_depth);
+	update_alloc_hint_after_get(sb, depth, hint, nr);
 
 	return nr;
 }
-EXPORT_SYMBOL_GPL(sbitmap_get_shallow);
 
 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)
+		if (sb->map[i].word & ~sb->map[i].cleared)
 			return true;
 	}
 	return false;
 }
 EXPORT_SYMBOL_GPL(sbitmap_any_bit_set);
 
-bool sbitmap_any_bit_clear(const struct sbitmap *sb)
+static unsigned int __sbitmap_weight(const struct sbitmap *sb, bool set)
 {
-	unsigned int i;
+	unsigned int i, weight = 0;
 
 	for (i = 0; i < sb->map_nr; i++) {
 		const struct sbitmap_word *word = &sb->map[i];
-		unsigned long ret;
+		unsigned int word_depth = __map_depth(sb, i);
 
-		ret = find_first_zero_bit(&word->word, word->depth);
-		if (ret < word->depth)
-			return true;
+		if (set)
+			weight += bitmap_weight(&word->word, word_depth);
+		else
+			weight += bitmap_weight(&word->cleared, word_depth);
 	}
-	return false;
+	return weight;
 }
-EXPORT_SYMBOL_GPL(sbitmap_any_bit_clear);
 
-unsigned int sbitmap_weight(const struct sbitmap *sb)
+static unsigned int sbitmap_cleared(const struct sbitmap *sb)
 {
-	unsigned int i, weight = 0;
-
-	for (i = 0; i < sb->map_nr; i++) {
-		const struct sbitmap_word *word = &sb->map[i];
+	return __sbitmap_weight(sb, false);
+}
 
-		weight += bitmap_weight(&word->word, word->depth);
-	}
-	return weight;
+unsigned int sbitmap_weight(const struct sbitmap *sb)
+{
+	return __sbitmap_weight(sb, true) - sbitmap_cleared(sb);
 }
 EXPORT_SYMBOL_GPL(sbitmap_weight);
 
@@ -218,6 +381,7 @@ void sbitmap_show(struct sbitmap *sb, struct seq_file *m)
 {
 	seq_printf(m, "depth=%u\n", sb->depth);
 	seq_printf(m, "busy=%u\n", sbitmap_weight(sb));
+	seq_printf(m, "cleared=%u\n", sbitmap_cleared(sb));
 	seq_printf(m, "bits_per_word=%u\n", 1U << sb->shift);
 	seq_printf(m, "map_nr=%u\n", sb->map_nr);
 }
@@ -244,7 +408,10 @@ void sbitmap_bitmap_show(struct sbitmap *sb, struct seq_file *m)
 
 	for (i = 0; i < sb->map_nr; i++) {
 		unsigned long word = READ_ONCE(sb->map[i].word);
-		unsigned int word_bits = READ_ONCE(sb->map[i].depth);
+		unsigned long cleared = READ_ONCE(sb->map[i].cleared);
+		unsigned int word_bits = __map_depth(sb, i);
+
+		word &= ~cleared;
 
 		while (word_bits > 0) {
 			unsigned int bits = min(8 - byte_bits, word_bits);
@@ -270,20 +437,12 @@ void sbitmap_bitmap_show(struct sbitmap *sb, struct seq_file *m)
 }
 EXPORT_SYMBOL_GPL(sbitmap_bitmap_show);
 
-static unsigned int sbq_calc_wake_batch(unsigned int depth)
+static unsigned int sbq_calc_wake_batch(struct sbitmap_queue *sbq,
+					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;
+	return clamp_t(unsigned int,
+		       min(depth, sbq->min_shallow_depth) / SBQ_WAIT_QUEUES,
+		       1, SBQ_WAKE_BATCH);
 }
 
 int sbitmap_queue_init_node(struct sbitmap_queue *sbq, unsigned int depth,
@@ -292,187 +451,253 @@ int sbitmap_queue_init_node(struct sbitmap_queue *sbq, unsigned int depth,
 	int ret;
 	int i;
 
-	ret = sbitmap_init_node(&sbq->sb, depth, shift, flags, node);
+	ret = sbitmap_init_node(&sbq->sb, depth, shift, flags, node,
+				round_robin, true);
 	if (ret)
 		return ret;
 
-	sbq->alloc_hint = alloc_percpu_gfp(unsigned int, flags);
-	if (!sbq->alloc_hint) {
-		sbitmap_free(&sbq->sb);
-		return -ENOMEM;
-	}
-
-	if (depth && !round_robin) {
-		for_each_possible_cpu(i)
-			*per_cpu_ptr(sbq->alloc_hint, i) = prandom_u32() % depth;
-	}
-
-	sbq->wake_batch = sbq_calc_wake_batch(depth);
+	sbq->min_shallow_depth = UINT_MAX;
+	sbq->wake_batch = sbq_calc_wake_batch(sbq, depth);
 	atomic_set(&sbq->wake_index, 0);
+	atomic_set(&sbq->ws_active, 0);
+	atomic_set(&sbq->completion_cnt, 0);
+	atomic_set(&sbq->wakeup_cnt, 0);
 
 	sbq->ws = kzalloc_node(SBQ_WAIT_QUEUES * sizeof(*sbq->ws), flags, node);
 	if (!sbq->ws) {
-		free_percpu(sbq->alloc_hint);
 		sbitmap_free(&sbq->sb);
 		return -ENOMEM;
 	}
 
-	for (i = 0; i < SBQ_WAIT_QUEUES; i++) {
+	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);
-	}
 
-	sbq->round_robin = round_robin;
 	return 0;
 }
 EXPORT_SYMBOL_GPL(sbitmap_queue_init_node);
 
-void sbitmap_queue_resize(struct sbitmap_queue *sbq, unsigned int depth)
+static void sbitmap_queue_update_wake_batch(struct sbitmap_queue *sbq,
+					    unsigned int depth)
 {
-	unsigned int wake_batch = sbq_calc_wake_batch(depth);
-	int i;
+	unsigned int wake_batch;
 
-	if (sbq->wake_batch != wake_batch) {
+	wake_batch = sbq_calc_wake_batch(sbq, depth);
+	if (sbq->wake_batch != wake_batch)
 		WRITE_ONCE(sbq->wake_batch, wake_batch);
-		/*
-		 * Pairs with the memory barrier in sbq_wake_up() to ensure that
-		 * the batch size is updated before the wait counts.
-		 */
-		smp_mb__before_atomic();
-		for (i = 0; i < SBQ_WAIT_QUEUES; i++)
-			atomic_set(&sbq->ws[i].wait_cnt, 1);
-	}
+}
+
+void sbitmap_queue_recalculate_wake_batch(struct sbitmap_queue *sbq,
+					    unsigned int users)
+{
+	unsigned int wake_batch;
+	unsigned int depth = (sbq->sb.depth + users - 1) / users;
+
+	wake_batch = clamp_val(depth / SBQ_WAIT_QUEUES,
+			1, SBQ_WAKE_BATCH);
+
+	WRITE_ONCE(sbq->wake_batch, wake_batch);
+}
+EXPORT_SYMBOL_GPL(sbitmap_queue_recalculate_wake_batch);
+
+void sbitmap_queue_resize(struct sbitmap_queue *sbq, unsigned int depth)
+{
+	sbitmap_queue_update_wake_batch(sbq, depth);
 	sbitmap_resize(&sbq->sb, depth);
 }
 EXPORT_SYMBOL_GPL(sbitmap_queue_resize);
 
 int __sbitmap_queue_get(struct sbitmap_queue *sbq)
 {
+	return sbitmap_get(&sbq->sb);
+}
+EXPORT_SYMBOL_GPL(__sbitmap_queue_get);
+
+unsigned long __sbitmap_queue_get_batch(struct sbitmap_queue *sbq, int nr_tags,
+					unsigned int *offset)
+{
+	struct sbitmap *sb = &sbq->sb;
 	unsigned int hint, depth;
-	int nr;
+	unsigned long index, nr;
+	int i;
 
-	hint = this_cpu_read(*sbq->alloc_hint);
-	depth = READ_ONCE(sbq->sb.depth);
-	if (unlikely(hint >= depth)) {
-		hint = depth ? prandom_u32() % depth : 0;
-		this_cpu_write(*sbq->alloc_hint, hint);
-	}
-	nr = sbitmap_get(&sbq->sb, hint, sbq->round_robin);
+	if (unlikely(sb->round_robin))
+		return 0;
 
-	if (nr == -1) {
-		/* If the map is full, a hint won't do us much good. */
-		this_cpu_write(*sbq->alloc_hint, 0);
-	} else if (nr == hint || unlikely(sbq->round_robin)) {
-		/* Only update the hint if we used it. */
-		hint = nr + 1;
-		if (hint >= depth - 1)
-			hint = 0;
-		this_cpu_write(*sbq->alloc_hint, hint);
+	depth = READ_ONCE(sb->depth);
+	hint = update_alloc_hint_before_get(sb, depth);
+
+	index = SB_NR_TO_INDEX(sb, hint);
+
+	for (i = 0; i < sb->map_nr; i++) {
+		struct sbitmap_word *map = &sb->map[index];
+		unsigned long get_mask;
+		unsigned int map_depth = __map_depth(sb, index);
+		unsigned long val;
+
+		sbitmap_deferred_clear(map, 0, 0, 0);
+		val = READ_ONCE(map->word);
+		if (val == (1UL << (map_depth - 1)) - 1)
+			goto next;
+
+		nr = find_first_zero_bit(&val, map_depth);
+		if (nr + nr_tags <= map_depth) {
+			atomic_long_t *ptr = (atomic_long_t *) &map->word;
+
+			get_mask = ((1UL << nr_tags) - 1) << nr;
+			while (!atomic_long_try_cmpxchg(ptr, &val,
+							  get_mask | val))
+				;
+			get_mask = (get_mask & ~val) >> nr;
+			if (get_mask) {
+				*offset = nr + (index << sb->shift);
+				update_alloc_hint_after_get(sb, depth, hint,
+							*offset + nr_tags - 1);
+				return get_mask;
+			}
+		}
+next:
+		/* Jump to next index. */
+		if (++index >= sb->map_nr)
+			index = 0;
 	}
 
-	return nr;
+	return 0;
 }
-EXPORT_SYMBOL_GPL(__sbitmap_queue_get);
 
-int __sbitmap_queue_get_shallow(struct sbitmap_queue *sbq,
-				unsigned int shallow_depth)
+int sbitmap_queue_get_shallow(struct sbitmap_queue *sbq,
+			      unsigned int shallow_depth)
 {
-	unsigned int hint, depth;
-	int nr;
-
-	hint = this_cpu_read(*sbq->alloc_hint);
-	depth = READ_ONCE(sbq->sb.depth);
-	if (unlikely(hint >= depth)) {
-		hint = depth ? prandom_u32() % depth : 0;
-		this_cpu_write(*sbq->alloc_hint, hint);
-	}
-	nr = sbitmap_get_shallow(&sbq->sb, hint, shallow_depth);
+	WARN_ON_ONCE(shallow_depth < sbq->min_shallow_depth);
 
-	if (nr == -1) {
-		/* If the map is full, a hint won't do us much good. */
-		this_cpu_write(*sbq->alloc_hint, 0);
-	} else if (nr == hint || unlikely(sbq->round_robin)) {
-		/* Only update the hint if we used it. */
-		hint = nr + 1;
-		if (hint >= depth - 1)
-			hint = 0;
-		this_cpu_write(*sbq->alloc_hint, hint);
-	}
+	return sbitmap_get_shallow(&sbq->sb, shallow_depth);
+}
+EXPORT_SYMBOL_GPL(sbitmap_queue_get_shallow);
 
-	return nr;
+void sbitmap_queue_min_shallow_depth(struct sbitmap_queue *sbq,
+				     unsigned int min_shallow_depth)
+{
+	sbq->min_shallow_depth = min_shallow_depth;
+	sbitmap_queue_update_wake_batch(sbq, sbq->sb.depth);
 }
-EXPORT_SYMBOL_GPL(__sbitmap_queue_get_shallow);
+EXPORT_SYMBOL_GPL(sbitmap_queue_min_shallow_depth);
 
-static struct sbq_wait_state *sbq_wake_ptr(struct sbitmap_queue *sbq)
+static void __sbitmap_queue_wake_up(struct sbitmap_queue *sbq, int nr)
 {
-	int i, wake_index;
+	int i, wake_index, woken;
+
+	if (!atomic_read(&sbq->ws_active))
+		return;
 
 	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);
+		/*
+		 * Advance the index before checking the current queue.
+		 * It improves fairness, by ensuring the queue doesn't
+		 * need to be fully emptied before trying to wake up
+		 * from the next one.
+		 */
+		wake_index = sbq_index_inc(wake_index);
 
-			if (wake_index != o)
-				atomic_cmpxchg(&sbq->wake_index, o, wake_index);
-			return ws;
+		if (waitqueue_active(&ws->wait)) {
+			woken = wake_up_nr(&ws->wait, nr);
+			if (woken == nr)
+				break;
+			nr -= woken;
 		}
-
-		wake_index = sbq_index_inc(wake_index);
 	}
 
-	return NULL;
+	if (wake_index != atomic_read(&sbq->wake_index))
+		atomic_set(&sbq->wake_index, wake_index);
 }
 
-static void sbq_wake_up(struct sbitmap_queue *sbq)
+void sbitmap_queue_wake_up(struct sbitmap_queue *sbq, int nr)
 {
-	struct sbq_wait_state *ws;
-	unsigned int wake_batch;
-	int wait_cnt;
-
-	/*
-	 * Pairs with the memory barrier in set_current_state() to ensure the
-	 * proper ordering of clear_bit()/waitqueue_active() in the waker and
-	 * test_and_set_bit()/prepare_to_wait()/finish_wait() in the waiter. See
-	 * the comment on waitqueue_active(). This is __after_atomic because we
-	 * just did clear_bit() in the caller.
-	 */
-	smp_mb__after_atomic();
+	unsigned int wake_batch = READ_ONCE(sbq->wake_batch);
+	unsigned int wakeups;
 
-	ws = sbq_wake_ptr(sbq);
-	if (!ws)
+	if (!atomic_read(&sbq->ws_active))
 		return;
 
-	wait_cnt = atomic_dec_return(&ws->wait_cnt);
-	if (wait_cnt <= 0) {
-		wake_batch = READ_ONCE(sbq->wake_batch);
-		/*
-		 * Pairs with the memory barrier in sbitmap_queue_resize() to
-		 * ensure that we see the batch size update before the wait
-		 * count is reset.
-		 */
-		smp_mb__before_atomic();
-		/*
-		 * If there are concurrent callers to sbq_wake_up(), the last
-		 * one to decrement the wait count below zero will bump it back
-		 * up. If there is a concurrent resize, the count reset will
-		 * either cause the cmpxchg to fail or overwrite after the
-		 * cmpxchg.
-		 */
-		atomic_cmpxchg(&ws->wait_cnt, wait_cnt, wait_cnt + wake_batch);
-		sbq_index_atomic_inc(&sbq->wake_index);
-		wake_up(&ws->wait);
+	atomic_add(nr, &sbq->completion_cnt);
+	wakeups = atomic_read(&sbq->wakeup_cnt);
+
+	do {
+		if (atomic_read(&sbq->completion_cnt) - wakeups < wake_batch)
+			return;
+	} while (!atomic_try_cmpxchg(&sbq->wakeup_cnt,
+				     &wakeups, wakeups + wake_batch));
+
+	__sbitmap_queue_wake_up(sbq, wake_batch);
+}
+EXPORT_SYMBOL_GPL(sbitmap_queue_wake_up);
+
+static inline void sbitmap_update_cpu_hint(struct sbitmap *sb, int cpu, int tag)
+{
+	if (likely(!sb->round_robin && tag < sb->depth))
+		data_race(*per_cpu_ptr(sb->alloc_hint, cpu) = tag);
+}
+
+void sbitmap_queue_clear_batch(struct sbitmap_queue *sbq, int offset,
+				int *tags, int nr_tags)
+{
+	struct sbitmap *sb = &sbq->sb;
+	unsigned long *addr = NULL;
+	unsigned long mask = 0;
+	int i;
+
+	smp_mb__before_atomic();
+	for (i = 0; i < nr_tags; i++) {
+		const int tag = tags[i] - offset;
+		unsigned long *this_addr;
+
+		/* since we're clearing a batch, skip the deferred map */
+		this_addr = &sb->map[SB_NR_TO_INDEX(sb, tag)].word;
+		if (!addr) {
+			addr = this_addr;
+		} else if (addr != this_addr) {
+			atomic_long_andnot(mask, (atomic_long_t *) addr);
+			mask = 0;
+			addr = this_addr;
+		}
+		mask |= (1UL << SB_NR_TO_BIT(sb, tag));
 	}
+
+	if (mask)
+		atomic_long_andnot(mask, (atomic_long_t *) addr);
+
+	smp_mb__after_atomic();
+	sbitmap_queue_wake_up(sbq, nr_tags);
+	sbitmap_update_cpu_hint(&sbq->sb, raw_smp_processor_id(),
+					tags[nr_tags - 1] - offset);
 }
 
 void sbitmap_queue_clear(struct sbitmap_queue *sbq, unsigned int nr,
 			 unsigned int cpu)
 {
-	sbitmap_clear_bit(&sbq->sb, nr);
-	sbq_wake_up(sbq);
-	if (likely(!sbq->round_robin && nr < sbq->sb.depth))
-		*per_cpu_ptr(sbq->alloc_hint, cpu) = nr;
+	/*
+	 * Once the clear bit is set, the bit may be allocated out.
+	 *
+	 * Orders READ/WRITE on the associated instance(such as request
+	 * of blk_mq) by this bit for avoiding race with re-allocation,
+	 * and its pair is the memory barrier implied in __sbitmap_get_word.
+	 *
+	 * One invariant is that the clear bit has to be zero when the bit
+	 * is in use.
+	 */
+	smp_mb__before_atomic();
+	sbitmap_deferred_clear_bit(&sbq->sb, nr);
+
+	/*
+	 * Pairs with the memory barrier in set_current_state() to ensure the
+	 * proper ordering of clear_bit_unlock()/waitqueue_active() in the waker
+	 * and test_and_set_bit_lock()/prepare_to_wait()/finish_wait() in the
+	 * waiter. See the comment on waitqueue_active().
+	 */
+	smp_mb__after_atomic();
+	sbitmap_queue_wake_up(sbq, 1);
+	sbitmap_update_cpu_hint(&sbq->sb, cpu, nr);
 }
 EXPORT_SYMBOL_GPL(sbitmap_queue_clear);
 
@@ -482,7 +707,7 @@ void sbitmap_queue_wake_all(struct sbitmap_queue *sbq)
 
 	/*
 	 * Pairs with the memory barrier in set_current_state() like in
-	 * sbq_wake_up().
+	 * sbitmap_queue_wake_up().
 	 */
 	smp_mb();
 	wake_index = atomic_read(&sbq->wake_index);
@@ -510,23 +735,68 @@ void sbitmap_queue_show(struct sbitmap_queue *sbq, struct seq_file *m)
 		if (!first)
 			seq_puts(m, ", ");
 		first = false;
-		seq_printf(m, "%u", *per_cpu_ptr(sbq->alloc_hint, i));
+		seq_printf(m, "%u", *per_cpu_ptr(sbq->sb.alloc_hint, i));
 	}
 	seq_puts(m, "}\n");
 
 	seq_printf(m, "wake_batch=%u\n", sbq->wake_batch);
 	seq_printf(m, "wake_index=%d\n", atomic_read(&sbq->wake_index));
+	seq_printf(m, "ws_active=%d\n", atomic_read(&sbq->ws_active));
 
 	seq_puts(m, "ws={\n");
 	for (i = 0; i < SBQ_WAIT_QUEUES; i++) {
 		struct sbq_wait_state *ws = &sbq->ws[i];
-
-		seq_printf(m, "\t{.wait_cnt=%d, .wait=%s},\n",
-			   atomic_read(&ws->wait_cnt),
+		seq_printf(m, "\t{.wait=%s},\n",
 			   waitqueue_active(&ws->wait) ? "active" : "inactive");
 	}
 	seq_puts(m, "}\n");
 
-	seq_printf(m, "round_robin=%d\n", sbq->round_robin);
+	seq_printf(m, "round_robin=%d\n", sbq->sb.round_robin);
+	seq_printf(m, "min_shallow_depth=%u\n", sbq->min_shallow_depth);
 }
 EXPORT_SYMBOL_GPL(sbitmap_queue_show);
+
+void sbitmap_add_wait_queue(struct sbitmap_queue *sbq,
+			    struct sbq_wait_state *ws,
+			    struct sbq_wait *sbq_wait)
+{
+	if (!sbq_wait->sbq) {
+		sbq_wait->sbq = sbq;
+		atomic_inc(&sbq->ws_active);
+		add_wait_queue(&ws->wait, &sbq_wait->wait);
+	}
+}
+EXPORT_SYMBOL_GPL(sbitmap_add_wait_queue);
+
+void sbitmap_del_wait_queue(struct sbq_wait *sbq_wait)
+{
+	list_del_init(&sbq_wait->wait.entry);
+	if (sbq_wait->sbq) {
+		atomic_dec(&sbq_wait->sbq->ws_active);
+		sbq_wait->sbq = NULL;
+	}
+}
+EXPORT_SYMBOL_GPL(sbitmap_del_wait_queue);
+
+void sbitmap_prepare_to_wait(struct sbitmap_queue *sbq,
+			     struct sbq_wait_state *ws,
+			     struct sbq_wait *sbq_wait, int state)
+{
+	if (!sbq_wait->sbq) {
+		atomic_inc(&sbq->ws_active);
+		sbq_wait->sbq = sbq;
+	}
+	prepare_to_wait_exclusive(&ws->wait, &sbq_wait->wait, state);
+}
+EXPORT_SYMBOL_GPL(sbitmap_prepare_to_wait);
+
+void sbitmap_finish_wait(struct sbitmap_queue *sbq, struct sbq_wait_state *ws,
+			 struct sbq_wait *sbq_wait)
+{
+	finish_wait(&ws->wait, &sbq_wait->wait);
+	if (sbq_wait->sbq) {
+		atomic_dec(&sbq->ws_active);
+		sbq_wait->sbq = NULL;
+	}
+}
+EXPORT_SYMBOL_GPL(sbitmap_finish_wait);