1 files changed, 1342 insertions, 596 deletions

diff --git a/drivers/md/dm-bufio.c b/drivers/md/dm-bufio.c
index cf077f9b30c3..8a448185662c 100644
--- a/drivers/md/dm-bufio.c
+++ b/drivers/md/dm-bufio.c
@@ -21,6 +21,8 @@
 #include <linux/stacktrace.h>
 #include <linux/jump_label.h>
 
+#include "dm.h"
+
 #define DM_MSG_PREFIX "bufio"
 
 /*
@@ -66,57 +68,241 @@
 #define LIST_DIRTY	1
 #define LIST_SIZE	2
 
+/*--------------------------------------------------------------*/
+
 /*
- * Linking of buffers:
- *	All buffers are linked to buffer_tree with their node field.
- *
- *	Clean buffers that are not being written (B_WRITING not set)
- *	are linked to lru[LIST_CLEAN] with their lru_list field.
- *
- *	Dirty and clean buffers that are being written are linked to
- *	lru[LIST_DIRTY] with their lru_list field. When the write
- *	finishes, the buffer cannot be relinked immediately (because we
- *	are in an interrupt context and relinking requires process
- *	context), so some clean-not-writing buffers can be held on
- *	dirty_lru too.  They are later added to lru in the process
- *	context.
+ * Rather than use an LRU list, we use a clock algorithm where entries
+ * are held in a circular list.  When an entry is 'hit' a reference bit
+ * is set.  The least recently used entry is approximated by running a
+ * cursor around the list selecting unreferenced entries. Referenced
+ * entries have their reference bit cleared as the cursor passes them.
  */
-struct dm_bufio_client {
-	struct mutex lock;
-	spinlock_t spinlock;
-	bool no_sleep;
+struct lru_entry {
+	struct list_head list;
+	atomic_t referenced;
+};
 
-	struct list_head lru[LIST_SIZE];
-	unsigned long n_buffers[LIST_SIZE];
+struct lru_iter {
+	struct lru *lru;
+	struct list_head list;
+	struct lru_entry *stop;
+	struct lru_entry *e;
+};
 
-	struct block_device *bdev;
-	unsigned int block_size;
-	s8 sectors_per_block_bits;
-	void (*alloc_callback)(struct dm_buffer *buf);
-	void (*write_callback)(struct dm_buffer *buf);
-	struct kmem_cache *slab_buffer;
-	struct kmem_cache *slab_cache;
-	struct dm_io_client *dm_io;
+struct lru {
+	struct list_head *cursor;
+	unsigned long count;
 
-	struct list_head reserved_buffers;
-	unsigned int need_reserved_buffers;
+	struct list_head iterators;
+};
 
-	unsigned int minimum_buffers;
+/*--------------*/
 
-	struct rb_root buffer_tree;
-	wait_queue_head_t free_buffer_wait;
+static void lru_init(struct lru *lru)
+{
+	lru->cursor = NULL;
+	lru->count = 0;
+	INIT_LIST_HEAD(&lru->iterators);
+}
 
-	sector_t start;
+static void lru_destroy(struct lru *lru)
+{
+	WARN_ON_ONCE(lru->cursor);
+	WARN_ON_ONCE(!list_empty(&lru->iterators));
+}
 
-	int async_write_error;
+/*
+ * Insert a new entry into the lru.
+ */
+static void lru_insert(struct lru *lru, struct lru_entry *le)
+{
+	/*
+	 * Don't be tempted to set to 1, makes the lru aspect
+	 * perform poorly.
+	 */
+	atomic_set(&le->referenced, 0);
 
-	struct list_head client_list;
+	if (lru->cursor) {
+		list_add_tail(&le->list, lru->cursor);
+	} else {
+		INIT_LIST_HEAD(&le->list);
+		lru->cursor = &le->list;
+	}
+	lru->count++;
+}
 
-	struct shrinker shrinker;
-	struct work_struct shrink_work;
-	atomic_long_t need_shrink;
+/*--------------*/
+
+/*
+ * Convert a list_head pointer to an lru_entry pointer.
+ */
+static inline struct lru_entry *to_le(struct list_head *l)
+{
+	return container_of(l, struct lru_entry, list);
+}
+
+/*
+ * Initialize an lru_iter and add it to the list of cursors in the lru.
+ */
+static void lru_iter_begin(struct lru *lru, struct lru_iter *it)
+{
+	it->lru = lru;
+	it->stop = lru->cursor ? to_le(lru->cursor->prev) : NULL;
+	it->e = lru->cursor ? to_le(lru->cursor) : NULL;
+	list_add(&it->list, &lru->iterators);
+}
+
+/*
+ * Remove an lru_iter from the list of cursors in the lru.
+ */
+static inline void lru_iter_end(struct lru_iter *it)
+{
+	list_del(&it->list);
+}
+
+/* Predicate function type to be used with lru_iter_next */
+typedef bool (*iter_predicate)(struct lru_entry *le, void *context);
+
+/*
+ * Advance the cursor to the next entry that passes the
+ * predicate, and return that entry.  Returns NULL if the
+ * iteration is complete.
+ */
+static struct lru_entry *lru_iter_next(struct lru_iter *it,
+				       iter_predicate pred, void *context)
+{
+	struct lru_entry *e;
+
+	while (it->e) {
+		e = it->e;
+
+		/* advance the cursor */
+		if (it->e == it->stop)
+			it->e = NULL;
+		else
+			it->e = to_le(it->e->list.next);
+
+		if (pred(e, context))
+			return e;
+	}
+
+	return NULL;
+}
+
+/*
+ * Invalidate a specific lru_entry and update all cursors in
+ * the lru accordingly.
+ */
+static void lru_iter_invalidate(struct lru *lru, struct lru_entry *e)
+{
+	struct lru_iter *it;
+
+	list_for_each_entry(it, &lru->iterators, list) {
+		/* Move c->e forwards if necc. */
+		if (it->e == e) {
+			it->e = to_le(it->e->list.next);
+			if (it->e == e)
+				it->e = NULL;
+		}
+
+		/* Move it->stop backwards if necc. */
+		if (it->stop == e) {
+			it->stop = to_le(it->stop->list.prev);
+			if (it->stop == e)
+				it->stop = NULL;
+		}
+	}
+}
+
+/*--------------*/
+
+/*
+ * Remove a specific entry from the lru.
+ */
+static void lru_remove(struct lru *lru, struct lru_entry *le)
+{
+	lru_iter_invalidate(lru, le);
+	if (lru->count == 1) {
+		lru->cursor = NULL;
+	} else {
+		if (lru->cursor == &le->list)
+			lru->cursor = lru->cursor->next;
+		list_del(&le->list);
+	}
+	lru->count--;
+}
+
+/*
+ * Mark as referenced.
+ */
+static inline void lru_reference(struct lru_entry *le)
+{
+	atomic_set(&le->referenced, 1);
+}
+
+/*--------------*/
+
+/*
+ * Remove the least recently used entry (approx), that passes the predicate.
+ * Returns NULL on failure.
+ */
+enum evict_result {
+	ER_EVICT,
+	ER_DONT_EVICT,
+	ER_STOP, /* stop looking for something to evict */
 };
 
+typedef enum evict_result (*le_predicate)(struct lru_entry *le, void *context);
+
+static struct lru_entry *lru_evict(struct lru *lru, le_predicate pred, void *context)
+{
+	unsigned long tested = 0;
+	struct list_head *h = lru->cursor;
+	struct lru_entry *le;
+
+	if (!h)
+		return NULL;
+	/*
+	 * In the worst case we have to loop around twice. Once to clear
+	 * the reference flags, and then again to discover the predicate
+	 * fails for all entries.
+	 */
+	while (tested < lru->count) {
+		le = container_of(h, struct lru_entry, list);
+
+		if (atomic_read(&le->referenced)) {
+			atomic_set(&le->referenced, 0);
+		} else {
+			tested++;
+			switch (pred(le, context)) {
+			case ER_EVICT:
+				/*
+				 * Adjust the cursor, so we start the next
+				 * search from here.
+				 */
+				lru->cursor = le->list.next;
+				lru_remove(lru, le);
+				return le;
+
+			case ER_DONT_EVICT:
+				break;
+
+			case ER_STOP:
+				lru->cursor = le->list.next;
+				return NULL;
+			}
+		}
+
+		h = h->next;
+
+		cond_resched();
+	}
+
+	return NULL;
+}
+
+/*--------------------------------------------------------------*/
+
 /*
  * Buffer state bits.
  */
@@ -137,26 +323,37 @@ enum data_mode {
 };
 
 struct dm_buffer {
+	/* protected by the locks in dm_buffer_cache */
 	struct rb_node node;
-	struct list_head lru_list;
-	struct list_head global_list;
+
+	/* immutable, so don't need protecting */
 	sector_t block;
 	void *data;
 	unsigned char data_mode;		/* DATA_MODE_* */
+
+	/*
+	 * These two fields are used in isolation, so do not need
+	 * a surrounding lock.
+	 */
+	atomic_t hold_count;
+	unsigned long last_accessed;
+
+	/*
+	 * Everything else is protected by the mutex in
+	 * dm_bufio_client
+	 */
+	unsigned long state;
+	struct lru_entry lru;
 	unsigned char list_mode;		/* LIST_* */
 	blk_status_t read_error;
 	blk_status_t write_error;
-	unsigned int accessed;
-	unsigned int hold_count;
-	unsigned long state;
-	unsigned long last_accessed;
 	unsigned int dirty_start;
 	unsigned int dirty_end;
 	unsigned int write_start;
 	unsigned int write_end;
-	struct dm_bufio_client *c;
 	struct list_head write_list;
-	void (*end_io)(struct dm_buffer *buf, blk_status_t stat);
+	struct dm_bufio_client *c;
+	void (*end_io)(struct dm_buffer *b, blk_status_t bs);
 #ifdef CONFIG_DM_DEBUG_BLOCK_STACK_TRACING
 #define MAX_STACK 10
 	unsigned int stack_len;
@@ -164,126 +361,507 @@ struct dm_buffer {
 #endif
 };
 
-static DEFINE_STATIC_KEY_FALSE(no_sleep_enabled);
+/*--------------------------------------------------------------*/
 
-/*----------------------------------------------------------------*/
+/*
+ * The buffer cache manages buffers, particularly:
+ *  - inc/dec of holder count
+ *  - setting the last_accessed field
+ *  - maintains clean/dirty state along with lru
+ *  - selecting buffers that match predicates
+ *
+ * It does *not* handle:
+ *  - allocation/freeing of buffers.
+ *  - IO
+ *  - Eviction or cache sizing.
+ *
+ * cache_get() and cache_put() are threadsafe, you do not need to
+ * protect these calls with a surrounding mutex.  All the other
+ * methods are not threadsafe; they do use locking primitives, but
+ * only enough to ensure get/put are threadsafe.
+ */
 
-#define dm_bufio_in_request()	(!!current->bio_list)
+struct buffer_tree {
+	struct rw_semaphore lock;
+	struct rb_root root;
+} ____cacheline_aligned_in_smp;
 
-static void dm_bufio_lock(struct dm_bufio_client *c)
+struct dm_buffer_cache {
+	struct lru lru[LIST_SIZE];
+	/*
+	 * We spread entries across multiple trees to reduce contention
+	 * on the locks.
+	 */
+	unsigned int num_locks;
+	struct buffer_tree trees[];
+};
+
+static inline unsigned int cache_index(sector_t block, unsigned int num_locks)
 {
-	if (static_branch_unlikely(&no_sleep_enabled) && c->no_sleep)
-		spin_lock_bh(&c->spinlock);
-	else
-		mutex_lock_nested(&c->lock, dm_bufio_in_request());
+	return dm_hash_locks_index(block, num_locks);
 }
 
-static int dm_bufio_trylock(struct dm_bufio_client *c)
+static inline void cache_read_lock(struct dm_buffer_cache *bc, sector_t block)
 {
-	if (static_branch_unlikely(&no_sleep_enabled) && c->no_sleep)
-		return spin_trylock_bh(&c->spinlock);
+	down_read(&bc->trees[cache_index(block, bc->num_locks)].lock);
+}
+
+static inline void cache_read_unlock(struct dm_buffer_cache *bc, sector_t block)
+{
+	up_read(&bc->trees[cache_index(block, bc->num_locks)].lock);
+}
+
+static inline void cache_write_lock(struct dm_buffer_cache *bc, sector_t block)
+{
+	down_write(&bc->trees[cache_index(block, bc->num_locks)].lock);
+}
+
+static inline void cache_write_unlock(struct dm_buffer_cache *bc, sector_t block)
+{
+	up_write(&bc->trees[cache_index(block, bc->num_locks)].lock);
+}
+
+/*
+ * Sometimes we want to repeatedly get and drop locks as part of an iteration.
+ * This struct helps avoid redundant drop and gets of the same lock.
+ */
+struct lock_history {
+	struct dm_buffer_cache *cache;
+	bool write;
+	unsigned int previous;
+	unsigned int no_previous;
+};
+
+static void lh_init(struct lock_history *lh, struct dm_buffer_cache *cache, bool write)
+{
+	lh->cache = cache;
+	lh->write = write;
+	lh->no_previous = cache->num_locks;
+	lh->previous = lh->no_previous;
+}
+
+static void __lh_lock(struct lock_history *lh, unsigned int index)
+{
+	if (lh->write)
+		down_write(&lh->cache->trees[index].lock);
 	else
-		return mutex_trylock(&c->lock);
+		down_read(&lh->cache->trees[index].lock);
 }
 
-static void dm_bufio_unlock(struct dm_bufio_client *c)
+static void __lh_unlock(struct lock_history *lh, unsigned int index)
 {
-	if (static_branch_unlikely(&no_sleep_enabled) && c->no_sleep)
-		spin_unlock_bh(&c->spinlock);
+	if (lh->write)
+		up_write(&lh->cache->trees[index].lock);
 	else
-		mutex_unlock(&c->lock);
+		up_read(&lh->cache->trees[index].lock);
 }
 
-/*----------------------------------------------------------------*/
+/*
+ * Make sure you call this since it will unlock the final lock.
+ */
+static void lh_exit(struct lock_history *lh)
+{
+	if (lh->previous != lh->no_previous) {
+		__lh_unlock(lh, lh->previous);
+		lh->previous = lh->no_previous;
+	}
+}
 
 /*
- * Default cache size: available memory divided by the ratio.
+ * Named 'next' because there is no corresponding
+ * 'up/unlock' call since it's done automatically.
  */
-static unsigned long dm_bufio_default_cache_size;
+static void lh_next(struct lock_history *lh, sector_t b)
+{
+	unsigned int index = cache_index(b, lh->no_previous); /* no_previous is num_locks */
+
+	if (lh->previous != lh->no_previous) {
+		if (lh->previous != index) {
+			__lh_unlock(lh, lh->previous);
+			__lh_lock(lh, index);
+			lh->previous = index;
+		}
+	} else {
+		__lh_lock(lh, index);
+		lh->previous = index;
+	}
+}
+
+static inline struct dm_buffer *le_to_buffer(struct lru_entry *le)
+{
+	return container_of(le, struct dm_buffer, lru);
+}
+
+static struct dm_buffer *list_to_buffer(struct list_head *l)
+{
+	struct lru_entry *le = list_entry(l, struct lru_entry, list);
+
+	if (!le)
+		return NULL;
+
+	return le_to_buffer(le);
+}
+
+static void cache_init(struct dm_buffer_cache *bc, unsigned int num_locks)
+{
+	unsigned int i;
+
+	bc->num_locks = num_locks;
+
+	for (i = 0; i < bc->num_locks; i++) {
+		init_rwsem(&bc->trees[i].lock);
+		bc->trees[i].root = RB_ROOT;
+	}
+
+	lru_init(&bc->lru[LIST_CLEAN]);
+	lru_init(&bc->lru[LIST_DIRTY]);
+}
+
+static void cache_destroy(struct dm_buffer_cache *bc)
+{
+	unsigned int i;
+
+	for (i = 0; i < bc->num_locks; i++)
+		WARN_ON_ONCE(!RB_EMPTY_ROOT(&bc->trees[i].root));
+
+	lru_destroy(&bc->lru[LIST_CLEAN]);
+	lru_destroy(&bc->lru[LIST_DIRTY]);
+}
+
+/*--------------*/
 
 /*
- * Total cache size set by the user.
+ * not threadsafe, or racey depending how you look at it
  */
-static unsigned long dm_bufio_cache_size;
+static inline unsigned long cache_count(struct dm_buffer_cache *bc, int list_mode)
+{
+	return bc->lru[list_mode].count;
+}
+
+static inline unsigned long cache_total(struct dm_buffer_cache *bc)
+{
+	return cache_count(bc, LIST_CLEAN) + cache_count(bc, LIST_DIRTY);
+}
+
+/*--------------*/
 
 /*
- * A copy of dm_bufio_cache_size because dm_bufio_cache_size can change
- * at any time.  If it disagrees, the user has changed cache size.
+ * Gets a specific buffer, indexed by block.
+ * If the buffer is found then its holder count will be incremented and
+ * lru_reference will be called.
+ *
+ * threadsafe
  */
-static unsigned long dm_bufio_cache_size_latch;
+static struct dm_buffer *__cache_get(const struct rb_root *root, sector_t block)
+{
+	struct rb_node *n = root->rb_node;
+	struct dm_buffer *b;
 
-static DEFINE_SPINLOCK(global_spinlock);
+	while (n) {
+		b = container_of(n, struct dm_buffer, node);
+
+		if (b->block == block)
+			return b;
+
+		n = block < b->block ? n->rb_left : n->rb_right;
+	}
+
+	return NULL;
+}
+
+static void __cache_inc_buffer(struct dm_buffer *b)
+{
+	atomic_inc(&b->hold_count);
+	WRITE_ONCE(b->last_accessed, jiffies);
+}
+
+static struct dm_buffer *cache_get(struct dm_buffer_cache *bc, sector_t block)
+{
+	struct dm_buffer *b;
+
+	cache_read_lock(bc, block);
+	b = __cache_get(&bc->trees[cache_index(block, bc->num_locks)].root, block);
+	if (b) {
+		lru_reference(&b->lru);
+		__cache_inc_buffer(b);
+	}
+	cache_read_unlock(bc, block);
 
-static LIST_HEAD(global_queue);
+	return b;
+}
 
-static unsigned long global_num;
+/*--------------*/
 
 /*
- * Buffers are freed after this timeout
+ * Returns true if the hold count hits zero.
+ * threadsafe
  */
-static unsigned int dm_bufio_max_age = DM_BUFIO_DEFAULT_AGE_SECS;
-static unsigned long dm_bufio_retain_bytes = DM_BUFIO_DEFAULT_RETAIN_BYTES;
+static bool cache_put(struct dm_buffer_cache *bc, struct dm_buffer *b)
+{
+	bool r;
 
-static unsigned long dm_bufio_peak_allocated;
-static unsigned long dm_bufio_allocated_kmem_cache;
-static unsigned long dm_bufio_allocated_get_free_pages;
-static unsigned long dm_bufio_allocated_vmalloc;
-static unsigned long dm_bufio_current_allocated;
+	cache_read_lock(bc, b->block);
+	BUG_ON(!atomic_read(&b->hold_count));
+	r = atomic_dec_and_test(&b->hold_count);
+	cache_read_unlock(bc, b->block);
 
-/*----------------------------------------------------------------*/
+	return r;
+}
+
+/*--------------*/
+
+typedef enum evict_result (*b_predicate)(struct dm_buffer *, void *);
 
 /*
- * The current number of clients.
+ * Evicts a buffer based on a predicate.  The oldest buffer that
+ * matches the predicate will be selected.  In addition to the
+ * predicate the hold_count of the selected buffer will be zero.
  */
-static int dm_bufio_client_count;
+struct evict_wrapper {
+	struct lock_history *lh;
+	b_predicate pred;
+	void *context;
+};
 
 /*
- * The list of all clients.
+ * Wraps the buffer predicate turning it into an lru predicate.  Adds
+ * extra test for hold_count.
  */
-static LIST_HEAD(dm_bufio_all_clients);
+static enum evict_result __evict_pred(struct lru_entry *le, void *context)
+{
+	struct evict_wrapper *w = context;
+	struct dm_buffer *b = le_to_buffer(le);
+
+	lh_next(w->lh, b->block);
+
+	if (atomic_read(&b->hold_count))
+		return ER_DONT_EVICT;
+
+	return w->pred(b, w->context);
+}
+
+static struct dm_buffer *__cache_evict(struct dm_buffer_cache *bc, int list_mode,
+				       b_predicate pred, void *context,
+				       struct lock_history *lh)
+{
+	struct evict_wrapper w = {.lh = lh, .pred = pred, .context = context};
+	struct lru_entry *le;
+	struct dm_buffer *b;
+
+	le = lru_evict(&bc->lru[list_mode], __evict_pred, &w);
+	if (!le)
+		return NULL;
+
+	b = le_to_buffer(le);
+	/* __evict_pred will have locked the appropriate tree. */
+	rb_erase(&b->node, &bc->trees[cache_index(b->block, bc->num_locks)].root);
+
+	return b;
+}
+
+static struct dm_buffer *cache_evict(struct dm_buffer_cache *bc, int list_mode,
+				     b_predicate pred, void *context)
+{
+	struct dm_buffer *b;
+	struct lock_history lh;
+
+	lh_init(&lh, bc, true);
+	b = __cache_evict(bc, list_mode, pred, context, &lh);
+	lh_exit(&lh);
+
+	return b;
+}
+
+/*--------------*/
 
 /*
- * This mutex protects dm_bufio_cache_size_latch and dm_bufio_client_count
+ * Mark a buffer as clean or dirty. Not threadsafe.
  */
-static DEFINE_MUTEX(dm_bufio_clients_lock);
+static void cache_mark(struct dm_buffer_cache *bc, struct dm_buffer *b, int list_mode)
+{
+	cache_write_lock(bc, b->block);
+	if (list_mode != b->list_mode) {
+		lru_remove(&bc->lru[b->list_mode], &b->lru);
+		b->list_mode = list_mode;
+		lru_insert(&bc->lru[b->list_mode], &b->lru);
+	}
+	cache_write_unlock(bc, b->block);
+}
 
-static struct workqueue_struct *dm_bufio_wq;
-static struct delayed_work dm_bufio_cleanup_old_work;
-static struct work_struct dm_bufio_replacement_work;
+/*--------------*/
 
+/*
+ * Runs through the lru associated with 'old_mode', if the predicate matches then
+ * it moves them to 'new_mode'.  Not threadsafe.
+ */
+static void __cache_mark_many(struct dm_buffer_cache *bc, int old_mode, int new_mode,
+			      b_predicate pred, void *context, struct lock_history *lh)
+{
+	struct lru_entry *le;
+	struct dm_buffer *b;
+	struct evict_wrapper w = {.lh = lh, .pred = pred, .context = context};
 
-#ifdef CONFIG_DM_DEBUG_BLOCK_STACK_TRACING
-static void buffer_record_stack(struct dm_buffer *b)
+	while (true) {
+		le = lru_evict(&bc->lru[old_mode], __evict_pred, &w);
+		if (!le)
+			break;
+
+		b = le_to_buffer(le);
+		b->list_mode = new_mode;
+		lru_insert(&bc->lru[b->list_mode], &b->lru);
+	}
+}
+
+static void cache_mark_many(struct dm_buffer_cache *bc, int old_mode, int new_mode,
+			    b_predicate pred, void *context)
 {
-	b->stack_len = stack_trace_save(b->stack_entries, MAX_STACK, 2);
+	struct lock_history lh;
+
+	lh_init(&lh, bc, true);
+	__cache_mark_many(bc, old_mode, new_mode, pred, context, &lh);
+	lh_exit(&lh);
 }
-#endif
+
+/*--------------*/
+
+/*
+ * Iterates through all clean or dirty entries calling a function for each
+ * entry.  The callback may terminate the iteration early.  Not threadsafe.
+ */
 
 /*
- *----------------------------------------------------------------
- * A red/black tree acts as an index for all the buffers.
- *----------------------------------------------------------------
+ * Iterator functions should return one of these actions to indicate
+ * how the iteration should proceed.
  */
-static struct dm_buffer *__find(struct dm_bufio_client *c, sector_t block)
+enum it_action {
+	IT_NEXT,
+	IT_COMPLETE,
+};
+
+typedef enum it_action (*iter_fn)(struct dm_buffer *b, void *context);
+
+static void __cache_iterate(struct dm_buffer_cache *bc, int list_mode,
+			    iter_fn fn, void *context, struct lock_history *lh)
 {
-	struct rb_node *n = c->buffer_tree.rb_node;
-	struct dm_buffer *b;
+	struct lru *lru = &bc->lru[list_mode];
+	struct lru_entry *le, *first;
 
-	while (n) {
-		b = container_of(n, struct dm_buffer, node);
+	if (!lru->cursor)
+		return;
 
-		if (b->block == block)
-			return b;
+	first = le = to_le(lru->cursor);
+	do {
+		struct dm_buffer *b = le_to_buffer(le);
 
-		n = block < b->block ? n->rb_left : n->rb_right;
+		lh_next(lh, b->block);
+
+		switch (fn(b, context)) {
+		case IT_NEXT:
+			break;
+
+		case IT_COMPLETE:
+			return;
+		}
+		cond_resched();
+
+		le = to_le(le->list.next);
+	} while (le != first);
+}
+
+static void cache_iterate(struct dm_buffer_cache *bc, int list_mode,
+			  iter_fn fn, void *context)
+{
+	struct lock_history lh;
+
+	lh_init(&lh, bc, false);
+	__cache_iterate(bc, list_mode, fn, context, &lh);
+	lh_exit(&lh);
+}
+
+/*--------------*/
+
+/*
+ * Passes ownership of the buffer to the cache. Returns false if the
+ * buffer was already present (in which case ownership does not pass).
+ * eg, a race with another thread.
+ *
+ * Holder count should be 1 on insertion.
+ *
+ * Not threadsafe.
+ */
+static bool __cache_insert(struct rb_root *root, struct dm_buffer *b)
+{
+	struct rb_node **new = &root->rb_node, *parent = NULL;
+	struct dm_buffer *found;
+
+	while (*new) {
+		found = container_of(*new, struct dm_buffer, node);
+
+		if (found->block == b->block)
+			return false;
+
+		parent = *new;
+		new = b->block < found->block ?
+			&found->node.rb_left : &found->node.rb_right;
 	}
 
-	return NULL;
+	rb_link_node(&b->node, parent, new);
+	rb_insert_color(&b->node, root);
+
+	return true;
+}
+
+static bool cache_insert(struct dm_buffer_cache *bc, struct dm_buffer *b)
+{
+	bool r;
+
+	if (WARN_ON_ONCE(b->list_mode >= LIST_SIZE))
+		return false;
+
+	cache_write_lock(bc, b->block);
+	BUG_ON(atomic_read(&b->hold_count) != 1);
+	r = __cache_insert(&bc->trees[cache_index(b->block, bc->num_locks)].root, b);
+	if (r)
+		lru_insert(&bc->lru[b->list_mode], &b->lru);
+	cache_write_unlock(bc, b->block);
+
+	return r;
 }
 
-static struct dm_buffer *__find_next(struct dm_bufio_client *c, sector_t block)
+/*--------------*/
+
+/*
+ * Removes buffer from cache, ownership of the buffer passes back to the caller.
+ * Fails if the hold_count is not one (ie. the caller holds the only reference).
+ *
+ * Not threadsafe.
+ */
+static bool cache_remove(struct dm_buffer_cache *bc, struct dm_buffer *b)
 {
-	struct rb_node *n = c->buffer_tree.rb_node;
+	bool r;
+
+	cache_write_lock(bc, b->block);
+
+	if (atomic_read(&b->hold_count) != 1) {
+		r = false;
+	} else {
+		r = true;
+		rb_erase(&b->node, &bc->trees[cache_index(b->block, bc->num_locks)].root);
+		lru_remove(&bc->lru[b->list_mode], &b->lru);
+	}
+
+	cache_write_unlock(bc, b->block);
+
+	return r;
+}
+
+/*--------------*/
+
+typedef void (*b_release)(struct dm_buffer *);
+
+static struct dm_buffer *__find_next(struct rb_root *root, sector_t block)
+{
+	struct rb_node *n = root->rb_node;
 	struct dm_buffer *b;
 	struct dm_buffer *best = NULL;
 
@@ -304,35 +882,188 @@ static struct dm_buffer *__find_next(struct dm_bufio_client *c, sector_t block)
 	return best;
 }
 
-static void __insert(struct dm_bufio_client *c, struct dm_buffer *b)
+static void __remove_range(struct dm_buffer_cache *bc,
+			   struct rb_root *root,
+			   sector_t begin, sector_t end,
+			   b_predicate pred, b_release release)
 {
-	struct rb_node **new = &c->buffer_tree.rb_node, *parent = NULL;
-	struct dm_buffer *found;
+	struct dm_buffer *b;
 
-	while (*new) {
-		found = container_of(*new, struct dm_buffer, node);
+	while (true) {
+		cond_resched();
 
-		if (found->block == b->block) {
-			BUG_ON(found != b);
-			return;
+		b = __find_next(root, begin);
+		if (!b || (b->block >= end))
+			break;
+
+		begin = b->block + 1;
+
+		if (atomic_read(&b->hold_count))
+			continue;
+
+		if (pred(b, NULL) == ER_EVICT) {
+			rb_erase(&b->node, root);
+			lru_remove(&bc->lru[b->list_mode], &b->lru);
+			release(b);
 		}
+	}
+}
 
-		parent = *new;
-		new = b->block < found->block ?
-			&found->node.rb_left : &found->node.rb_right;
+static void cache_remove_range(struct dm_buffer_cache *bc,
+			       sector_t begin, sector_t end,
+			       b_predicate pred, b_release release)
+{
+	unsigned int i;
+
+	for (i = 0; i < bc->num_locks; i++) {
+		down_write(&bc->trees[i].lock);
+		__remove_range(bc, &bc->trees[i].root, begin, end, pred, release);
+		up_write(&bc->trees[i].lock);
 	}
+}
 
-	rb_link_node(&b->node, parent, new);
-	rb_insert_color(&b->node, &c->buffer_tree);
+/*----------------------------------------------------------------*/
+
+/*
+ * Linking of buffers:
+ *	All buffers are linked to buffer_cache with their node field.
+ *
+ *	Clean buffers that are not being written (B_WRITING not set)
+ *	are linked to lru[LIST_CLEAN] with their lru_list field.
+ *
+ *	Dirty and clean buffers that are being written are linked to
+ *	lru[LIST_DIRTY] with their lru_list field. When the write
+ *	finishes, the buffer cannot be relinked immediately (because we
+ *	are in an interrupt context and relinking requires process
+ *	context), so some clean-not-writing buffers can be held on
+ *	dirty_lru too.  They are later added to lru in the process
+ *	context.
+ */
+struct dm_bufio_client {
+	struct block_device *bdev;
+	unsigned int block_size;
+	s8 sectors_per_block_bits;
+
+	bool no_sleep;
+	struct mutex lock;
+	spinlock_t spinlock;
+
+	int async_write_error;
+
+	void (*alloc_callback)(struct dm_buffer *buf);
+	void (*write_callback)(struct dm_buffer *buf);
+	struct kmem_cache *slab_buffer;
+	struct kmem_cache *slab_cache;
+	struct dm_io_client *dm_io;
+
+	struct list_head reserved_buffers;
+	unsigned int need_reserved_buffers;
+
+	unsigned int minimum_buffers;
+
+	sector_t start;
+
+	struct shrinker shrinker;
+	struct work_struct shrink_work;
+	atomic_long_t need_shrink;
+
+	wait_queue_head_t free_buffer_wait;
+
+	struct list_head client_list;
+
+	/*
+	 * Used by global_cleanup to sort the clients list.
+	 */
+	unsigned long oldest_buffer;
+
+	struct dm_buffer_cache cache; /* must be last member */
+};
+
+static DEFINE_STATIC_KEY_FALSE(no_sleep_enabled);
+
+/*----------------------------------------------------------------*/
+
+#define dm_bufio_in_request()	(!!current->bio_list)
+
+static void dm_bufio_lock(struct dm_bufio_client *c)
+{
+	if (static_branch_unlikely(&no_sleep_enabled) && c->no_sleep)
+		spin_lock_bh(&c->spinlock);
+	else
+		mutex_lock_nested(&c->lock, dm_bufio_in_request());
 }
 
-static void __remove(struct dm_bufio_client *c, struct dm_buffer *b)
+static void dm_bufio_unlock(struct dm_bufio_client *c)
 {
-	rb_erase(&b->node, &c->buffer_tree);
+	if (static_branch_unlikely(&no_sleep_enabled) && c->no_sleep)
+		spin_unlock_bh(&c->spinlock);
+	else
+		mutex_unlock(&c->lock);
 }
 
 /*----------------------------------------------------------------*/
 
+/*
+ * Default cache size: available memory divided by the ratio.
+ */
+static unsigned long dm_bufio_default_cache_size;
+
+/*
+ * Total cache size set by the user.
+ */
+static unsigned long dm_bufio_cache_size;
+
+/*
+ * A copy of dm_bufio_cache_size because dm_bufio_cache_size can change
+ * at any time.  If it disagrees, the user has changed cache size.
+ */
+static unsigned long dm_bufio_cache_size_latch;
+
+static DEFINE_SPINLOCK(global_spinlock);
+
+/*
+ * Buffers are freed after this timeout
+ */
+static unsigned int dm_bufio_max_age = DM_BUFIO_DEFAULT_AGE_SECS;
+static unsigned long dm_bufio_retain_bytes = DM_BUFIO_DEFAULT_RETAIN_BYTES;
+
+static unsigned long dm_bufio_peak_allocated;
+static unsigned long dm_bufio_allocated_kmem_cache;
+static unsigned long dm_bufio_allocated_get_free_pages;
+static unsigned long dm_bufio_allocated_vmalloc;
+static unsigned long dm_bufio_current_allocated;
+
+/*----------------------------------------------------------------*/
+
+/*
+ * The current number of clients.
+ */
+static int dm_bufio_client_count;
+
+/*
+ * The list of all clients.
+ */
+static LIST_HEAD(dm_bufio_all_clients);
+
+/*
+ * This mutex protects dm_bufio_cache_size_latch and dm_bufio_client_count
+ */
+static DEFINE_MUTEX(dm_bufio_clients_lock);
+
+static struct workqueue_struct *dm_bufio_wq;
+static struct delayed_work dm_bufio_cleanup_old_work;
+static struct work_struct dm_bufio_replacement_work;
+
+
+#ifdef CONFIG_DM_DEBUG_BLOCK_STACK_TRACING
+static void buffer_record_stack(struct dm_buffer *b)
+{
+	b->stack_len = stack_trace_save(b->stack_entries, MAX_STACK, 2);
+}
+#endif
+
+/*----------------------------------------------------------------*/
+
 static void adjust_total_allocated(struct dm_buffer *b, bool unlink)
 {
 	unsigned char data_mode;
@@ -358,16 +1089,9 @@ static void adjust_total_allocated(struct dm_buffer *b, bool unlink)
 	if (dm_bufio_current_allocated > dm_bufio_peak_allocated)
 		dm_bufio_peak_allocated = dm_bufio_current_allocated;
 
-	b->accessed = 1;
-
 	if (!unlink) {
-		list_add(&b->global_list, &global_queue);
-		global_num++;
 		if (dm_bufio_current_allocated > dm_bufio_cache_size)
 			queue_work(dm_bufio_wq, &dm_bufio_replacement_work);
-	} else {
-		list_del(&b->global_list);
-		global_num--;
 	}
 
 	spin_unlock(&global_spinlock);
@@ -378,8 +1102,10 @@ static void adjust_total_allocated(struct dm_buffer *b, bool unlink)
  */
 static void __cache_size_refresh(void)
 {
-	BUG_ON(!mutex_is_locked(&dm_bufio_clients_lock));
-	BUG_ON(dm_bufio_client_count < 0);
+	if (WARN_ON(!mutex_is_locked(&dm_bufio_clients_lock)))
+		return;
+	if (WARN_ON(dm_bufio_client_count < 0))
+		return;
 
 	dm_bufio_cache_size_latch = READ_ONCE(dm_bufio_cache_size);
 
@@ -495,6 +1221,7 @@ static struct dm_buffer *alloc_buffer(struct dm_bufio_client *c, gfp_t gfp_mask)
 		kmem_cache_free(c->slab_buffer, b);
 		return NULL;
 	}
+	adjust_total_allocated(b, false);
 
 #ifdef CONFIG_DM_DEBUG_BLOCK_STACK_TRACING
 	b->stack_len = 0;
@@ -509,62 +1236,12 @@ static void free_buffer(struct dm_buffer *b)
 {
 	struct dm_bufio_client *c = b->c;
 
+	adjust_total_allocated(b, true);
 	free_buffer_data(c, b->data, b->data_mode);
 	kmem_cache_free(c->slab_buffer, b);
 }
 
 /*
- * Link buffer to the buffer tree and clean or dirty queue.
- */
-static void __link_buffer(struct dm_buffer *b, sector_t block, int dirty)
-{
-	struct dm_bufio_client *c = b->c;
-
-	c->n_buffers[dirty]++;
-	b->block = block;
-	b->list_mode = dirty;
-	list_add(&b->lru_list, &c->lru[dirty]);
-	__insert(b->c, b);
-	b->last_accessed = jiffies;
-
-	adjust_total_allocated(b, false);
-}
-
-/*
- * Unlink buffer from the buffer tree and dirty or clean queue.
- */
-static void __unlink_buffer(struct dm_buffer *b)
-{
-	struct dm_bufio_client *c = b->c;
-
-	BUG_ON(!c->n_buffers[b->list_mode]);
-
-	c->n_buffers[b->list_mode]--;
-	__remove(b->c, b);
-	list_del(&b->lru_list);
-
-	adjust_total_allocated(b, true);
-}
-
-/*
- * Place the buffer to the head of dirty or clean LRU queue.
- */
-static void __relink_lru(struct dm_buffer *b, int dirty)
-{
-	struct dm_bufio_client *c = b->c;
-
-	b->accessed = 1;
-
-	BUG_ON(!c->n_buffers[b->list_mode]);
-
-	c->n_buffers[b->list_mode]--;
-	c->n_buffers[dirty]++;
-	b->list_mode = dirty;
-	list_move(&b->lru_list, &c->lru[dirty]);
-	b->last_accessed = jiffies;
-}
-
-/*
  *--------------------------------------------------------------------------
  * Submit I/O on the buffer.
  *
@@ -639,19 +1316,14 @@ static void use_bio(struct dm_buffer *b, enum req_op op, sector_t sector,
 {
 	struct bio *bio;
 	char *ptr;
-	unsigned int vec_size, len;
+	unsigned int len;
 
-	vec_size = b->c->block_size >> PAGE_SHIFT;
-	if (unlikely(b->c->sectors_per_block_bits < PAGE_SHIFT - SECTOR_SHIFT))
-		vec_size += 2;
-
-	bio = bio_kmalloc(vec_size, GFP_NOWAIT | __GFP_NORETRY | __GFP_NOWARN);
+	bio = bio_kmalloc(1, GFP_NOWAIT | __GFP_NORETRY | __GFP_NOWARN);
 	if (!bio) {
-dmio:
 		use_dmio(b, op, sector, n_sectors, offset);
 		return;
 	}
-	bio_init(bio, b->c->bdev, bio->bi_inline_vecs, vec_size, op);
+	bio_init(bio, b->c->bdev, bio->bi_inline_vecs, 1, op);
 	bio->bi_iter.bi_sector = sector;
 	bio->bi_end_io = bio_complete;
 	bio->bi_private = b;
@@ -659,18 +1331,7 @@ dmio:
 	ptr = (char *)b->data + offset;
 	len = n_sectors << SECTOR_SHIFT;
 
-	do {
-		unsigned int this_step = min((unsigned int)(PAGE_SIZE - offset_in_page(ptr)), len);
-
-		if (!bio_add_page(bio, virt_to_page(ptr), this_step,
-				  offset_in_page(ptr))) {
-			bio_put(bio);
-			goto dmio;
-		}
-
-		len -= this_step;
-		ptr += this_step;
-	} while (len > 0);
+	__bio_add_page(bio, virt_to_page(ptr), len, offset_in_page(ptr));
 
 	submit_bio(bio);
 }
@@ -803,7 +1464,7 @@ static void __flush_write_list(struct list_head *write_list)
  */
 static void __make_buffer_clean(struct dm_buffer *b)
 {
-	BUG_ON(b->hold_count);
+	BUG_ON(atomic_read(&b->hold_count));
 
 	/* smp_load_acquire() pairs with read_endio()'s smp_mb__before_atomic() */
 	if (!smp_load_acquire(&b->state))	/* fast case */
@@ -814,6 +1475,36 @@ static void __make_buffer_clean(struct dm_buffer *b)
 	wait_on_bit_io(&b->state, B_WRITING, TASK_UNINTERRUPTIBLE);
 }
 
+static enum evict_result is_clean(struct dm_buffer *b, void *context)
+{
+	struct dm_bufio_client *c = context;
+
+	/* These should never happen */
+	if (WARN_ON_ONCE(test_bit(B_WRITING, &b->state)))
+		return ER_DONT_EVICT;
+	if (WARN_ON_ONCE(test_bit(B_DIRTY, &b->state)))
+		return ER_DONT_EVICT;
+	if (WARN_ON_ONCE(b->list_mode != LIST_CLEAN))
+		return ER_DONT_EVICT;
+
+	if (static_branch_unlikely(&no_sleep_enabled) && c->no_sleep &&
+	    unlikely(test_bit(B_READING, &b->state)))
+		return ER_DONT_EVICT;
+
+	return ER_EVICT;
+}
+
+static enum evict_result is_dirty(struct dm_buffer *b, void *context)
+{
+	/* These should never happen */
+	if (WARN_ON_ONCE(test_bit(B_READING, &b->state)))
+		return ER_DONT_EVICT;
+	if (WARN_ON_ONCE(b->list_mode != LIST_DIRTY))
+		return ER_DONT_EVICT;
+
+	return ER_EVICT;
+}
+
 /*
  * Find some buffer that is not held by anybody, clean it, unlink it and
  * return it.
@@ -822,34 +1513,20 @@ static struct dm_buffer *__get_unclaimed_buffer(struct dm_bufio_client *c)
 {
 	struct dm_buffer *b;
 
-	list_for_each_entry_reverse(b, &c->lru[LIST_CLEAN], lru_list) {
-		BUG_ON(test_bit(B_WRITING, &b->state));
-		BUG_ON(test_bit(B_DIRTY, &b->state));
-
-		if (static_branch_unlikely(&no_sleep_enabled) && c->no_sleep &&
-		    unlikely(test_bit_acquire(B_READING, &b->state)))
-			continue;
-
-		if (!b->hold_count) {
-			__make_buffer_clean(b);
-			__unlink_buffer(b);
-			return b;
-		}
-		cond_resched();
+	b = cache_evict(&c->cache, LIST_CLEAN, is_clean, c);
+	if (b) {
+		/* this also waits for pending reads */
+		__make_buffer_clean(b);
+		return b;
 	}
 
 	if (static_branch_unlikely(&no_sleep_enabled) && c->no_sleep)
 		return NULL;
 
-	list_for_each_entry_reverse(b, &c->lru[LIST_DIRTY], lru_list) {
-		BUG_ON(test_bit(B_READING, &b->state));
-
-		if (!b->hold_count) {
-			__make_buffer_clean(b);
-			__unlink_buffer(b);
-			return b;
-		}
-		cond_resched();
+	b = cache_evict(&c->cache, LIST_DIRTY, is_dirty, NULL);
+	if (b) {
+		__make_buffer_clean(b);
+		return b;
 	}
 
 	return NULL;
@@ -870,7 +1547,12 @@ static void __wait_for_free_buffer(struct dm_bufio_client *c)
 	set_current_state(TASK_UNINTERRUPTIBLE);
 	dm_bufio_unlock(c);
 
-	io_schedule();
+	/*
+	 * It's possible to miss a wake up event since we don't always
+	 * hold c->lock when wake_up is called.  So we have a timeout here,
+	 * just in case.
+	 */
+	io_schedule_timeout(5 * HZ);
 
 	remove_wait_queue(&c->free_buffer_wait, &wait);
 
@@ -928,9 +1610,8 @@ static struct dm_buffer *__alloc_buffer_wait_no_callback(struct dm_bufio_client
 		}
 
 		if (!list_empty(&c->reserved_buffers)) {
-			b = list_entry(c->reserved_buffers.next,
-				       struct dm_buffer, lru_list);
-			list_del(&b->lru_list);
+			b = list_to_buffer(c->reserved_buffers.next);
+			list_del(&b->lru.list);
 			c->need_reserved_buffers++;
 
 			return b;
@@ -964,36 +1645,61 @@ static void __free_buffer_wake(struct dm_buffer *b)
 {
 	struct dm_bufio_client *c = b->c;
 
+	b->block = -1;
 	if (!c->need_reserved_buffers)
 		free_buffer(b);
 	else {
-		list_add(&b->lru_list, &c->reserved_buffers);
+		list_add(&b->lru.list, &c->reserved_buffers);
 		c->need_reserved_buffers--;
 	}
 
-	wake_up(&c->free_buffer_wait);
+	/*
+	 * We hold the bufio lock here, so no one can add entries to the
+	 * wait queue anyway.
+	 */
+	if (unlikely(waitqueue_active(&c->free_buffer_wait)))
+		wake_up(&c->free_buffer_wait);
 }
 
-static void __write_dirty_buffers_async(struct dm_bufio_client *c, int no_wait,
-					struct list_head *write_list)
+static enum evict_result cleaned(struct dm_buffer *b, void *context)
 {
-	struct dm_buffer *b, *tmp;
+	if (WARN_ON_ONCE(test_bit(B_READING, &b->state)))
+		return ER_DONT_EVICT; /* should never happen */
 
-	list_for_each_entry_safe_reverse(b, tmp, &c->lru[LIST_DIRTY], lru_list) {
-		BUG_ON(test_bit(B_READING, &b->state));
+	if (test_bit(B_DIRTY, &b->state) || test_bit(B_WRITING, &b->state))
+		return ER_DONT_EVICT;
+	else
+		return ER_EVICT;
+}
 
-		if (!test_bit(B_DIRTY, &b->state) &&
-		    !test_bit(B_WRITING, &b->state)) {
-			__relink_lru(b, LIST_CLEAN);
-			continue;
-		}
+static void __move_clean_buffers(struct dm_bufio_client *c)
+{
+	cache_mark_many(&c->cache, LIST_DIRTY, LIST_CLEAN, cleaned, NULL);
+}
 
-		if (no_wait && test_bit(B_WRITING, &b->state))
-			return;
+struct write_context {
+	int no_wait;
+	struct list_head *write_list;
+};
 
-		__write_dirty_buffer(b, write_list);
-		cond_resched();
-	}
+static enum it_action write_one(struct dm_buffer *b, void *context)
+{
+	struct write_context *wc = context;
+
+	if (wc->no_wait && test_bit(B_WRITING, &b->state))
+		return IT_COMPLETE;
+
+	__write_dirty_buffer(b, wc->write_list);
+	return IT_NEXT;
+}
+
+static void __write_dirty_buffers_async(struct dm_bufio_client *c, int no_wait,
+					struct list_head *write_list)
+{
+	struct write_context wc = {.no_wait = no_wait, .write_list = write_list};
+
+	__move_clean_buffers(c);
+	cache_iterate(&c->cache, LIST_DIRTY, write_one, &wc);
 }
 
 /*
@@ -1004,7 +1710,8 @@ static void __write_dirty_buffers_async(struct dm_bufio_client *c, int no_wait,
 static void __check_watermark(struct dm_bufio_client *c,
 			      struct list_head *write_list)
 {
-	if (c->n_buffers[LIST_DIRTY] > c->n_buffers[LIST_CLEAN] * DM_BUFIO_WRITEBACK_RATIO)
+	if (cache_count(&c->cache, LIST_DIRTY) >
+	    cache_count(&c->cache, LIST_CLEAN) * DM_BUFIO_WRITEBACK_RATIO)
 		__write_dirty_buffers_async(c, 1, write_list);
 }
 
@@ -1014,6 +1721,21 @@ static void __check_watermark(struct dm_bufio_client *c,
  *--------------------------------------------------------------
  */
 
+static void cache_put_and_wake(struct dm_bufio_client *c, struct dm_buffer *b)
+{
+	/*
+	 * Relying on waitqueue_active() is racey, but we sleep
+	 * with schedule_timeout anyway.
+	 */
+	if (cache_put(&c->cache, b) &&
+	    unlikely(waitqueue_active(&c->free_buffer_wait)))
+		wake_up(&c->free_buffer_wait);
+}
+
+/*
+ * This assumes you have already checked the cache to see if the buffer
+ * is already present (it will recheck after dropping the lock for allocation).
+ */
 static struct dm_buffer *__bufio_new(struct dm_bufio_client *c, sector_t block,
 				     enum new_flag nf, int *need_submit,
 				     struct list_head *write_list)
@@ -1022,11 +1744,8 @@ static struct dm_buffer *__bufio_new(struct dm_bufio_client *c, sector_t block,
 
 	*need_submit = 0;
 
-	b = __find(c, block);
-	if (b)
-		goto found_buffer;
-
-	if (nf == NF_GET)
+	/* This can't be called with NF_GET */
+	if (WARN_ON_ONCE(nf == NF_GET))
 		return NULL;
 
 	new_b = __alloc_buffer_wait(c, nf);
@@ -1037,7 +1756,7 @@ static struct dm_buffer *__bufio_new(struct dm_bufio_client *c, sector_t block,
 	 * We've had a period where the mutex was unlocked, so need to
 	 * recheck the buffer tree.
 	 */
-	b = __find(c, block);
+	b = cache_get(&c->cache, block);
 	if (b) {
 		__free_buffer_wake(new_b);
 		goto found_buffer;
@@ -1046,24 +1765,35 @@ static struct dm_buffer *__bufio_new(struct dm_bufio_client *c, sector_t block,
 	__check_watermark(c, write_list);
 
 	b = new_b;
-	b->hold_count = 1;
+	atomic_set(&b->hold_count, 1);
+	WRITE_ONCE(b->last_accessed, jiffies);
+	b->block = block;
 	b->read_error = 0;
 	b->write_error = 0;
-	__link_buffer(b, block, LIST_CLEAN);
+	b->list_mode = LIST_CLEAN;
 
-	if (nf == NF_FRESH) {
+	if (nf == NF_FRESH)
 		b->state = 0;
-		return b;
+	else {
+		b->state = 1 << B_READING;
+		*need_submit = 1;
 	}
 
-	b->state = 1 << B_READING;
-	*need_submit = 1;
+	/*
+	 * We mustn't insert into the cache until the B_READING state
+	 * is set.  Otherwise another thread could get it and use
+	 * it before it had been read.
+	 */
+	cache_insert(&c->cache, b);
 
 	return b;
 
 found_buffer:
-	if (nf == NF_PREFETCH)
+	if (nf == NF_PREFETCH) {
+		cache_put_and_wake(c, b);
 		return NULL;
+	}
+
 	/*
 	 * Note: it is essential that we don't wait for the buffer to be
 	 * read if dm_bufio_get function is used. Both dm_bufio_get and
@@ -1071,12 +1801,11 @@ found_buffer:
 	 * If the user called both dm_bufio_prefetch and dm_bufio_get on
 	 * the same buffer, it would deadlock if we waited.
 	 */
-	if (nf == NF_GET && unlikely(test_bit_acquire(B_READING, &b->state)))
+	if (nf == NF_GET && unlikely(test_bit_acquire(B_READING, &b->state))) {
+		cache_put_and_wake(c, b);
 		return NULL;
+	}
 
-	b->hold_count++;
-	__relink_lru(b, test_bit(B_DIRTY, &b->state) ||
-		     test_bit(B_WRITING, &b->state));
 	return b;
 }
 
@@ -1106,18 +1835,50 @@ static void read_endio(struct dm_buffer *b, blk_status_t status)
 static void *new_read(struct dm_bufio_client *c, sector_t block,
 		      enum new_flag nf, struct dm_buffer **bp)
 {
-	int need_submit;
+	int need_submit = 0;
 	struct dm_buffer *b;
 
 	LIST_HEAD(write_list);
 
-	dm_bufio_lock(c);
-	b = __bufio_new(c, block, nf, &need_submit, &write_list);
+	*bp = NULL;
+
+	/*
+	 * Fast path, hopefully the block is already in the cache.  No need
+	 * to get the client lock for this.
+	 */
+	b = cache_get(&c->cache, block);
+	if (b) {
+		if (nf == NF_PREFETCH) {
+			cache_put_and_wake(c, b);
+			return NULL;
+		}
+
+		/*
+		 * Note: it is essential that we don't wait for the buffer to be
+		 * read if dm_bufio_get function is used. Both dm_bufio_get and
+		 * dm_bufio_prefetch can be used in the driver request routine.
+		 * If the user called both dm_bufio_prefetch and dm_bufio_get on
+		 * the same buffer, it would deadlock if we waited.
+		 */
+		if (nf == NF_GET && unlikely(test_bit_acquire(B_READING, &b->state))) {
+			cache_put_and_wake(c, b);
+			return NULL;
+		}
+	}
+
+	if (!b) {
+		if (nf == NF_GET)
+			return NULL;
+
+		dm_bufio_lock(c);
+		b = __bufio_new(c, block, nf, &need_submit, &write_list);
+		dm_bufio_unlock(c);
+	}
+
 #ifdef CONFIG_DM_DEBUG_BLOCK_STACK_TRACING
-	if (b && b->hold_count == 1)
+	if (b && (atomic_read(&b->hold_count) == 1))
 		buffer_record_stack(b);
 #endif
-	dm_bufio_unlock(c);
 
 	__flush_write_list(&write_list);
 
@@ -1152,7 +1913,8 @@ EXPORT_SYMBOL_GPL(dm_bufio_get);
 void *dm_bufio_read(struct dm_bufio_client *c, sector_t block,
 		    struct dm_buffer **bp)
 {
-	BUG_ON(dm_bufio_in_request());
+	if (WARN_ON_ONCE(dm_bufio_in_request()))
+		return ERR_PTR(-EINVAL);
 
 	return new_read(c, block, NF_READ, bp);
 }
@@ -1161,7 +1923,8 @@ EXPORT_SYMBOL_GPL(dm_bufio_read);
 void *dm_bufio_new(struct dm_bufio_client *c, sector_t block,
 		   struct dm_buffer **bp)
 {
-	BUG_ON(dm_bufio_in_request());
+	if (WARN_ON_ONCE(dm_bufio_in_request()))
+		return ERR_PTR(-EINVAL);
 
 	return new_read(c, block, NF_FRESH, bp);
 }
@@ -1174,15 +1937,23 @@ void dm_bufio_prefetch(struct dm_bufio_client *c,
 
 	LIST_HEAD(write_list);
 
-	BUG_ON(dm_bufio_in_request());
+	if (WARN_ON_ONCE(dm_bufio_in_request()))
+		return; /* should never happen */
 
 	blk_start_plug(&plug);
-	dm_bufio_lock(c);
 
 	for (; n_blocks--; block++) {
 		int need_submit;
 		struct dm_buffer *b;
 
+		b = cache_get(&c->cache, block);
+		if (b) {
+			/* already in cache */
+			cache_put_and_wake(c, b);
+			continue;
+		}
+
+		dm_bufio_lock(c);
 		b = __bufio_new(c, block, NF_PREFETCH, &need_submit,
 				&write_list);
 		if (unlikely(!list_empty(&write_list))) {
@@ -1205,10 +1976,9 @@ void dm_bufio_prefetch(struct dm_bufio_client *c,
 				goto flush_plug;
 			dm_bufio_lock(c);
 		}
+		dm_bufio_unlock(c);
 	}
 
-	dm_bufio_unlock(c);
-
 flush_plug:
 	blk_finish_plug(&plug);
 }
@@ -1218,29 +1988,28 @@ void dm_bufio_release(struct dm_buffer *b)
 {
 	struct dm_bufio_client *c = b->c;
 
-	dm_bufio_lock(c);
-
-	BUG_ON(!b->hold_count);
-
-	b->hold_count--;
-	if (!b->hold_count) {
-		wake_up(&c->free_buffer_wait);
+	/*
+	 * If there were errors on the buffer, and the buffer is not
+	 * to be written, free the buffer. There is no point in caching
+	 * invalid buffer.
+	 */
+	if ((b->read_error || b->write_error) &&
+	    !test_bit_acquire(B_READING, &b->state) &&
+	    !test_bit(B_WRITING, &b->state) &&
+	    !test_bit(B_DIRTY, &b->state)) {
+		dm_bufio_lock(c);
 
-		/*
-		 * If there were errors on the buffer, and the buffer is not
-		 * to be written, free the buffer. There is no point in caching
-		 * invalid buffer.
-		 */
-		if ((b->read_error || b->write_error) &&
-		    !test_bit_acquire(B_READING, &b->state) &&
-		    !test_bit(B_WRITING, &b->state) &&
-		    !test_bit(B_DIRTY, &b->state)) {
-			__unlink_buffer(b);
+		/* cache remove can fail if there are other holders */
+		if (cache_remove(&c->cache, b)) {
 			__free_buffer_wake(b);
+			dm_bufio_unlock(c);
+			return;
 		}
+
+		dm_bufio_unlock(c);
 	}
 
-	dm_bufio_unlock(c);
+	cache_put_and_wake(c, b);
 }
 EXPORT_SYMBOL_GPL(dm_bufio_release);
 
@@ -1259,7 +2028,7 @@ void dm_bufio_mark_partial_buffer_dirty(struct dm_buffer *b,
 	if (!test_and_set_bit(B_DIRTY, &b->state)) {
 		b->dirty_start = start;
 		b->dirty_end = end;
-		__relink_lru(b, LIST_DIRTY);
+		cache_mark(&c->cache, b, LIST_DIRTY);
 	} else {
 		if (start < b->dirty_start)
 			b->dirty_start = start;
@@ -1281,7 +2050,8 @@ void dm_bufio_write_dirty_buffers_async(struct dm_bufio_client *c)
 {
 	LIST_HEAD(write_list);
 
-	BUG_ON(dm_bufio_in_request());
+	if (WARN_ON_ONCE(dm_bufio_in_request()))
+		return; /* should never happen */
 
 	dm_bufio_lock(c);
 	__write_dirty_buffers_async(c, 0, &write_list);
@@ -1297,11 +2067,19 @@ EXPORT_SYMBOL_GPL(dm_bufio_write_dirty_buffers_async);
  *
  * Finally, we flush hardware disk cache.
  */
+static bool is_writing(struct lru_entry *e, void *context)
+{
+	struct dm_buffer *b = le_to_buffer(e);
+
+	return test_bit(B_WRITING, &b->state);
+}
+
 int dm_bufio_write_dirty_buffers(struct dm_bufio_client *c)
 {
 	int a, f;
-	unsigned long buffers_processed = 0;
-	struct dm_buffer *b, *tmp;
+	unsigned long nr_buffers;
+	struct lru_entry *e;
+	struct lru_iter it;
 
 	LIST_HEAD(write_list);
 
@@ -1311,52 +2089,32 @@ int dm_bufio_write_dirty_buffers(struct dm_bufio_client *c)
 	__flush_write_list(&write_list);
 	dm_bufio_lock(c);
 
-again:
-	list_for_each_entry_safe_reverse(b, tmp, &c->lru[LIST_DIRTY], lru_list) {
-		int dropped_lock = 0;
-
-		if (buffers_processed < c->n_buffers[LIST_DIRTY])
-			buffers_processed++;
+	nr_buffers = cache_count(&c->cache, LIST_DIRTY);
+	lru_iter_begin(&c->cache.lru[LIST_DIRTY], &it);
+	while ((e = lru_iter_next(&it, is_writing, c))) {
+		struct dm_buffer *b = le_to_buffer(e);
+		__cache_inc_buffer(b);
 
 		BUG_ON(test_bit(B_READING, &b->state));
 
-		if (test_bit(B_WRITING, &b->state)) {
-			if (buffers_processed < c->n_buffers[LIST_DIRTY]) {
-				dropped_lock = 1;
-				b->hold_count++;
-				dm_bufio_unlock(c);
-				wait_on_bit_io(&b->state, B_WRITING,
-					       TASK_UNINTERRUPTIBLE);
-				dm_bufio_lock(c);
-				b->hold_count--;
-			} else
-				wait_on_bit_io(&b->state, B_WRITING,
-					       TASK_UNINTERRUPTIBLE);
+		if (nr_buffers) {
+			nr_buffers--;
+			dm_bufio_unlock(c);
+			wait_on_bit_io(&b->state, B_WRITING, TASK_UNINTERRUPTIBLE);
+			dm_bufio_lock(c);
+		} else {
+			wait_on_bit_io(&b->state, B_WRITING, TASK_UNINTERRUPTIBLE);
 		}
 
-		if (!test_bit(B_DIRTY, &b->state) &&
-		    !test_bit(B_WRITING, &b->state))
-			__relink_lru(b, LIST_CLEAN);
+		if (!test_bit(B_DIRTY, &b->state) && !test_bit(B_WRITING, &b->state))
+			cache_mark(&c->cache, b, LIST_CLEAN);
 
-		cond_resched();
+		cache_put_and_wake(c, b);
 
-		/*
-		 * If we dropped the lock, the list is no longer consistent,
-		 * so we must restart the search.
-		 *
-		 * In the most common case, the buffer just processed is
-		 * relinked to the clean list, so we won't loop scanning the
-		 * same buffer again and again.
-		 *
-		 * This may livelock if there is another thread simultaneously
-		 * dirtying buffers, so we count the number of buffers walked
-		 * and if it exceeds the total number of buffers, it means that
-		 * someone is doing some writes simultaneously with us.  In
-		 * this case, stop, dropping the lock.
-		 */
-		if (dropped_lock)
-			goto again;
+		cond_resched();
 	}
+	lru_iter_end(&it);
+
 	wake_up(&c->free_buffer_wait);
 	dm_bufio_unlock(c);
 
@@ -1386,7 +2144,8 @@ int dm_bufio_issue_flush(struct dm_bufio_client *c)
 		.count = 0,
 	};
 
-	BUG_ON(dm_bufio_in_request());
+	if (WARN_ON_ONCE(dm_bufio_in_request()))
+		return -EINVAL;
 
 	return dm_io(&io_req, 1, &io_reg, NULL);
 }
@@ -1409,95 +2168,30 @@ int dm_bufio_issue_discard(struct dm_bufio_client *c, sector_t block, sector_t c
 		.count = block_to_sector(c, count),
 	};
 
-	BUG_ON(dm_bufio_in_request());
+	if (WARN_ON_ONCE(dm_bufio_in_request()))
+		return -EINVAL; /* discards are optional */
 
 	return dm_io(&io_req, 1, &io_reg, NULL);
 }
 EXPORT_SYMBOL_GPL(dm_bufio_issue_discard);
 
-/*
- * We first delete any other buffer that may be at that new location.
- *
- * Then, we write the buffer to the original location if it was dirty.
- *
- * Then, if we are the only one who is holding the buffer, relink the buffer
- * in the buffer tree for the new location.
- *
- * If there was someone else holding the buffer, we write it to the new
- * location but not relink it, because that other user needs to have the buffer
- * at the same place.
- */
-void dm_bufio_release_move(struct dm_buffer *b, sector_t new_block)
+static bool forget_buffer(struct dm_bufio_client *c, sector_t block)
 {
-	struct dm_bufio_client *c = b->c;
-	struct dm_buffer *new;
-
-	BUG_ON(dm_bufio_in_request());
-
-	dm_bufio_lock(c);
+	struct dm_buffer *b;
 
-retry:
-	new = __find(c, new_block);
-	if (new) {
-		if (new->hold_count) {
-			__wait_for_free_buffer(c);
-			goto retry;
+	b = cache_get(&c->cache, block);
+	if (b) {
+		if (likely(!smp_load_acquire(&b->state))) {
+			if (cache_remove(&c->cache, b))
+				__free_buffer_wake(b);
+			else
+				cache_put_and_wake(c, b);
+		} else {
+			cache_put_and_wake(c, b);
 		}
-
-		/*
-		 * FIXME: Is there any point waiting for a write that's going
-		 * to be overwritten in a bit?
-		 */
-		__make_buffer_clean(new);
-		__unlink_buffer(new);
-		__free_buffer_wake(new);
 	}
 
-	BUG_ON(!b->hold_count);
-	BUG_ON(test_bit(B_READING, &b->state));
-
-	__write_dirty_buffer(b, NULL);
-	if (b->hold_count == 1) {
-		wait_on_bit_io(&b->state, B_WRITING,
-			       TASK_UNINTERRUPTIBLE);
-		set_bit(B_DIRTY, &b->state);
-		b->dirty_start = 0;
-		b->dirty_end = c->block_size;
-		__unlink_buffer(b);
-		__link_buffer(b, new_block, LIST_DIRTY);
-	} else {
-		sector_t old_block;
-
-		wait_on_bit_lock_io(&b->state, B_WRITING,
-				    TASK_UNINTERRUPTIBLE);
-		/*
-		 * Relink buffer to "new_block" so that write_callback
-		 * sees "new_block" as a block number.
-		 * After the write, link the buffer back to old_block.
-		 * All this must be done in bufio lock, so that block number
-		 * change isn't visible to other threads.
-		 */
-		old_block = b->block;
-		__unlink_buffer(b);
-		__link_buffer(b, new_block, b->list_mode);
-		submit_io(b, REQ_OP_WRITE, write_endio);
-		wait_on_bit_io(&b->state, B_WRITING,
-			       TASK_UNINTERRUPTIBLE);
-		__unlink_buffer(b);
-		__link_buffer(b, old_block, b->list_mode);
-	}
-
-	dm_bufio_unlock(c);
-	dm_bufio_release(b);
-}
-EXPORT_SYMBOL_GPL(dm_bufio_release_move);
-
-static void forget_buffer_locked(struct dm_buffer *b)
-{
-	if (likely(!b->hold_count) && likely(!smp_load_acquire(&b->state))) {
-		__unlink_buffer(b);
-		__free_buffer_wake(b);
-	}
+	return b ? true : false;
 }
 
 /*
@@ -1508,38 +2202,22 @@ static void forget_buffer_locked(struct dm_buffer *b)
  */
 void dm_bufio_forget(struct dm_bufio_client *c, sector_t block)
 {
-	struct dm_buffer *b;
-
 	dm_bufio_lock(c);
-
-	b = __find(c, block);
-	if (b)
-		forget_buffer_locked(b);
-
+	forget_buffer(c, block);
 	dm_bufio_unlock(c);
 }
 EXPORT_SYMBOL_GPL(dm_bufio_forget);
 
-void dm_bufio_forget_buffers(struct dm_bufio_client *c, sector_t block, sector_t n_blocks)
+static enum evict_result idle(struct dm_buffer *b, void *context)
 {
-	struct dm_buffer *b;
-	sector_t end_block = block + n_blocks;
-
-	while (block < end_block) {
-		dm_bufio_lock(c);
-
-		b = __find_next(c, block);
-		if (b) {
-			block = b->block + 1;
-			forget_buffer_locked(b);
-		}
-
-		dm_bufio_unlock(c);
-
-		if (!b)
-			break;
-	}
+	return b->state ? ER_DONT_EVICT : ER_EVICT;
+}
 
+void dm_bufio_forget_buffers(struct dm_bufio_client *c, sector_t block, sector_t n_blocks)
+{
+	dm_bufio_lock(c);
+	cache_remove_range(&c->cache, block, block + n_blocks, idle, __free_buffer_wake);
+	dm_bufio_unlock(c);
 }
 EXPORT_SYMBOL_GPL(dm_bufio_forget_buffers);
 
@@ -1601,13 +2279,29 @@ struct dm_bufio_client *dm_bufio_get_client(struct dm_buffer *b)
 }
 EXPORT_SYMBOL_GPL(dm_bufio_get_client);
 
+static enum it_action warn_leak(struct dm_buffer *b, void *context)
+{
+	bool *warned = context;
+
+	WARN_ON(!(*warned));
+	*warned = true;
+	DMERR("leaked buffer %llx, hold count %u, list %d",
+	      (unsigned long long)b->block, atomic_read(&b->hold_count), b->list_mode);
+#ifdef CONFIG_DM_DEBUG_BLOCK_STACK_TRACING
+	stack_trace_print(b->stack_entries, b->stack_len, 1);
+	/* mark unclaimed to avoid WARN_ON at end of drop_buffers() */
+	atomic_set(&b->hold_count, 0);
+#endif
+	return IT_NEXT;
+}
+
 static void drop_buffers(struct dm_bufio_client *c)
 {
-	struct dm_buffer *b;
 	int i;
-	bool warned = false;
+	struct dm_buffer *b;
 
-	BUG_ON(dm_bufio_in_request());
+	if (WARN_ON(dm_bufio_in_request()))
+		return; /* should never happen */
 
 	/*
 	 * An optimization so that the buffers are not written one-by-one.
@@ -1619,18 +2313,11 @@ static void drop_buffers(struct dm_bufio_client *c)
 	while ((b = __get_unclaimed_buffer(c)))
 		__free_buffer_wake(b);
 
-	for (i = 0; i < LIST_SIZE; i++)
-		list_for_each_entry(b, &c->lru[i], lru_list) {
-			WARN_ON(!warned);
-			warned = true;
-			DMERR("leaked buffer %llx, hold count %u, list %d",
-			      (unsigned long long)b->block, b->hold_count, i);
-#ifdef CONFIG_DM_DEBUG_BLOCK_STACK_TRACING
-			stack_trace_print(b->stack_entries, b->stack_len, 1);
-			/* mark unclaimed to avoid BUG_ON below */
-			b->hold_count = 0;
-#endif
-		}
+	for (i = 0; i < LIST_SIZE; i++) {
+		bool warned = false;
+
+		cache_iterate(&c->cache, i, warn_leak, &warned);
+	}
 
 #ifdef CONFIG_DM_DEBUG_BLOCK_STACK_TRACING
 	while ((b = __get_unclaimed_buffer(c)))
@@ -1638,39 +2325,11 @@ static void drop_buffers(struct dm_bufio_client *c)
 #endif
 
 	for (i = 0; i < LIST_SIZE; i++)
-		BUG_ON(!list_empty(&c->lru[i]));
+		WARN_ON(cache_count(&c->cache, i));
 
 	dm_bufio_unlock(c);
 }
 
-/*
- * We may not be able to evict this buffer if IO pending or the client
- * is still using it.  Caller is expected to know buffer is too old.
- *
- * And if GFP_NOFS is used, we must not do any I/O because we hold
- * dm_bufio_clients_lock and we would risk deadlock if the I/O gets
- * rerouted to different bufio client.
- */
-static bool __try_evict_buffer(struct dm_buffer *b, gfp_t gfp)
-{
-	if (!(gfp & __GFP_FS) ||
-	    (static_branch_unlikely(&no_sleep_enabled) && b->c->no_sleep)) {
-		if (test_bit_acquire(B_READING, &b->state) ||
-		    test_bit(B_WRITING, &b->state) ||
-		    test_bit(B_DIRTY, &b->state))
-			return false;
-	}
-
-	if (b->hold_count)
-		return false;
-
-	__make_buffer_clean(b);
-	__unlink_buffer(b);
-	__free_buffer_wake(b);
-
-	return true;
-}
-
 static unsigned long get_retain_buffers(struct dm_bufio_client *c)
 {
 	unsigned long retain_bytes = READ_ONCE(dm_bufio_retain_bytes);
@@ -1686,22 +2345,28 @@ static unsigned long get_retain_buffers(struct dm_bufio_client *c)
 static void __scan(struct dm_bufio_client *c)
 {
 	int l;
-	struct dm_buffer *b, *tmp;
+	struct dm_buffer *b;
 	unsigned long freed = 0;
-	unsigned long count = c->n_buffers[LIST_CLEAN] +
-			      c->n_buffers[LIST_DIRTY];
 	unsigned long retain_target = get_retain_buffers(c);
+	unsigned long count = cache_total(&c->cache);
 
 	for (l = 0; l < LIST_SIZE; l++) {
-		list_for_each_entry_safe_reverse(b, tmp, &c->lru[l], lru_list) {
+		while (true) {
 			if (count - freed <= retain_target)
 				atomic_long_set(&c->need_shrink, 0);
 			if (!atomic_long_read(&c->need_shrink))
-				return;
-			if (__try_evict_buffer(b, GFP_KERNEL)) {
-				atomic_long_dec(&c->need_shrink);
-				freed++;
-			}
+				break;
+
+			b = cache_evict(&c->cache, l,
+					l == LIST_CLEAN ? is_clean : is_dirty, c);
+			if (!b)
+				break;
+
+			__make_buffer_clean(b);
+			__free_buffer_wake(b);
+
+			atomic_long_dec(&c->need_shrink);
+			freed++;
 			cond_resched();
 		}
 	}
@@ -1730,8 +2395,7 @@ static unsigned long dm_bufio_shrink_scan(struct shrinker *shrink, struct shrink
 static unsigned long dm_bufio_shrink_count(struct shrinker *shrink, struct shrink_control *sc)
 {
 	struct dm_bufio_client *c = container_of(shrink, struct dm_bufio_client, shrinker);
-	unsigned long count = READ_ONCE(c->n_buffers[LIST_CLEAN]) +
-			      READ_ONCE(c->n_buffers[LIST_DIRTY]);
+	unsigned long count = cache_total(&c->cache);
 	unsigned long retain_target = get_retain_buffers(c);
 	unsigned long queued_for_cleanup = atomic_long_read(&c->need_shrink);
 
@@ -1758,8 +2422,8 @@ struct dm_bufio_client *dm_bufio_client_create(struct block_device *bdev, unsign
 					       unsigned int flags)
 {
 	int r;
+	unsigned int num_locks;
 	struct dm_bufio_client *c;
-	unsigned int i;
 	char slab_name[27];
 
 	if (!block_size || block_size & ((1 << SECTOR_SHIFT) - 1)) {
@@ -1768,12 +2432,13 @@ struct dm_bufio_client *dm_bufio_client_create(struct block_device *bdev, unsign
 		goto bad_client;
 	}
 
-	c = kzalloc(sizeof(*c), GFP_KERNEL);
+	num_locks = dm_num_hash_locks();
+	c = kzalloc(sizeof(*c) + (num_locks * sizeof(struct buffer_tree)), GFP_KERNEL);
 	if (!c) {
 		r = -ENOMEM;
 		goto bad_client;
 	}
-	c->buffer_tree = RB_ROOT;
+	cache_init(&c->cache, num_locks);
 
 	c->bdev = bdev;
 	c->block_size = block_size;
@@ -1790,11 +2455,6 @@ struct dm_bufio_client *dm_bufio_client_create(struct block_device *bdev, unsign
 		static_branch_inc(&no_sleep_enabled);
 	}
 
-	for (i = 0; i < LIST_SIZE; i++) {
-		INIT_LIST_HEAD(&c->lru[i]);
-		c->n_buffers[i] = 0;
-	}
-
 	mutex_init(&c->lock);
 	spin_lock_init(&c->spinlock);
 	INIT_LIST_HEAD(&c->reserved_buffers);
@@ -1866,9 +2526,9 @@ struct dm_bufio_client *dm_bufio_client_create(struct block_device *bdev, unsign
 
 bad:
 	while (!list_empty(&c->reserved_buffers)) {
-		struct dm_buffer *b = list_entry(c->reserved_buffers.next,
-						 struct dm_buffer, lru_list);
-		list_del(&b->lru_list);
+		struct dm_buffer *b = list_to_buffer(c->reserved_buffers.next);
+
+		list_del(&b->lru.list);
 		free_buffer(b);
 	}
 	kmem_cache_destroy(c->slab_cache);
@@ -1905,23 +2565,23 @@ void dm_bufio_client_destroy(struct dm_bufio_client *c)
 
 	mutex_unlock(&dm_bufio_clients_lock);
 
-	BUG_ON(!RB_EMPTY_ROOT(&c->buffer_tree));
-	BUG_ON(c->need_reserved_buffers);
+	WARN_ON(c->need_reserved_buffers);
 
 	while (!list_empty(&c->reserved_buffers)) {
-		struct dm_buffer *b = list_entry(c->reserved_buffers.next,
-						 struct dm_buffer, lru_list);
-		list_del(&b->lru_list);
+		struct dm_buffer *b = list_to_buffer(c->reserved_buffers.next);
+
+		list_del(&b->lru.list);
 		free_buffer(b);
 	}
 
 	for (i = 0; i < LIST_SIZE; i++)
-		if (c->n_buffers[i])
-			DMERR("leaked buffer count %d: %ld", i, c->n_buffers[i]);
+		if (cache_count(&c->cache, i))
+			DMERR("leaked buffer count %d: %lu", i, cache_count(&c->cache, i));
 
 	for (i = 0; i < LIST_SIZE; i++)
-		BUG_ON(c->n_buffers[i]);
+		WARN_ON(cache_count(&c->cache, i));
 
+	cache_destroy(&c->cache);
 	kmem_cache_destroy(c->slab_cache);
 	kmem_cache_destroy(c->slab_buffer);
 	dm_io_client_destroy(c->dm_io);
@@ -1938,6 +2598,8 @@ void dm_bufio_set_sector_offset(struct dm_bufio_client *c, sector_t start)
 }
 EXPORT_SYMBOL_GPL(dm_bufio_set_sector_offset);
 
+/*--------------------------------------------------------------*/
+
 static unsigned int get_max_age_hz(void)
 {
 	unsigned int max_age = READ_ONCE(dm_bufio_max_age);
@@ -1950,13 +2612,74 @@ static unsigned int get_max_age_hz(void)
 
 static bool older_than(struct dm_buffer *b, unsigned long age_hz)
 {
-	return time_after_eq(jiffies, b->last_accessed + age_hz);
+	return time_after_eq(jiffies, READ_ONCE(b->last_accessed) + age_hz);
+}
+
+struct evict_params {
+	gfp_t gfp;
+	unsigned long age_hz;
+
+	/*
+	 * This gets updated with the largest last_accessed (ie. most
+	 * recently used) of the evicted buffers.  It will not be reinitialised
+	 * by __evict_many(), so you can use it across multiple invocations.
+	 */
+	unsigned long last_accessed;
+};
+
+/*
+ * We may not be able to evict this buffer if IO pending or the client
+ * is still using it.
+ *
+ * And if GFP_NOFS is used, we must not do any I/O because we hold
+ * dm_bufio_clients_lock and we would risk deadlock if the I/O gets
+ * rerouted to different bufio client.
+ */
+static enum evict_result select_for_evict(struct dm_buffer *b, void *context)
+{
+	struct evict_params *params = context;
+
+	if (!(params->gfp & __GFP_FS) ||
+	    (static_branch_unlikely(&no_sleep_enabled) && b->c->no_sleep)) {
+		if (test_bit_acquire(B_READING, &b->state) ||
+		    test_bit(B_WRITING, &b->state) ||
+		    test_bit(B_DIRTY, &b->state))
+			return ER_DONT_EVICT;
+	}
+
+	return older_than(b, params->age_hz) ? ER_EVICT : ER_STOP;
 }
 
-static void __evict_old_buffers(struct dm_bufio_client *c, unsigned long age_hz)
+static unsigned long __evict_many(struct dm_bufio_client *c,
+				  struct evict_params *params,
+				  int list_mode, unsigned long max_count)
 {
-	struct dm_buffer *b, *tmp;
-	unsigned long retain_target = get_retain_buffers(c);
+	unsigned long count;
+	unsigned long last_accessed;
+	struct dm_buffer *b;
+
+	for (count = 0; count < max_count; count++) {
+		b = cache_evict(&c->cache, list_mode, select_for_evict, params);
+		if (!b)
+			break;
+
+		last_accessed = READ_ONCE(b->last_accessed);
+		if (time_after_eq(params->last_accessed, last_accessed))
+			params->last_accessed = last_accessed;
+
+		__make_buffer_clean(b);
+		__free_buffer_wake(b);
+
+		cond_resched();
+	}
+
+	return count;
+}
+
+static void evict_old_buffers(struct dm_bufio_client *c, unsigned long age_hz)
+{
+	struct evict_params params = {.gfp = 0, .age_hz = age_hz, .last_accessed = 0};
+	unsigned long retain = get_retain_buffers(c);
 	unsigned long count;
 	LIST_HEAD(write_list);
 
@@ -1969,112 +2692,135 @@ static void __evict_old_buffers(struct dm_bufio_client *c, unsigned long age_hz)
 		dm_bufio_lock(c);
 	}
 
-	count = c->n_buffers[LIST_CLEAN] + c->n_buffers[LIST_DIRTY];
-	list_for_each_entry_safe_reverse(b, tmp, &c->lru[LIST_CLEAN], lru_list) {
-		if (count <= retain_target)
-			break;
-
-		if (!older_than(b, age_hz))
-			break;
-
-		if (__try_evict_buffer(b, 0))
-			count--;
-
-		cond_resched();
-	}
+	count = cache_total(&c->cache);
+	if (count > retain)
+		__evict_many(c, &params, LIST_CLEAN, count - retain);
 
 	dm_bufio_unlock(c);
 }
 
-static void do_global_cleanup(struct work_struct *w)
+static void cleanup_old_buffers(void)
 {
-	struct dm_bufio_client *locked_client = NULL;
-	struct dm_bufio_client *current_client;
-	struct dm_buffer *b;
-	unsigned int spinlock_hold_count;
-	unsigned long threshold = dm_bufio_cache_size -
-		dm_bufio_cache_size / DM_BUFIO_LOW_WATERMARK_RATIO;
-	unsigned long loops = global_num * 2;
+	unsigned long max_age_hz = get_max_age_hz();
+	struct dm_bufio_client *c;
 
 	mutex_lock(&dm_bufio_clients_lock);
 
-	while (1) {
-		cond_resched();
+	__cache_size_refresh();
 
-		spin_lock(&global_spinlock);
-		if (unlikely(dm_bufio_current_allocated <= threshold))
-			break;
+	list_for_each_entry(c, &dm_bufio_all_clients, client_list)
+		evict_old_buffers(c, max_age_hz);
 
-		spinlock_hold_count = 0;
-get_next:
-		if (!loops--)
-			break;
-		if (unlikely(list_empty(&global_queue)))
-			break;
-		b = list_entry(global_queue.prev, struct dm_buffer, global_list);
-
-		if (b->accessed) {
-			b->accessed = 0;
-			list_move(&b->global_list, &global_queue);
-			if (likely(++spinlock_hold_count < 16))
-				goto get_next;
-			spin_unlock(&global_spinlock);
-			continue;
-		}
+	mutex_unlock(&dm_bufio_clients_lock);
+}
 
-		current_client = b->c;
-		if (unlikely(current_client != locked_client)) {
-			if (locked_client)
-				dm_bufio_unlock(locked_client);
+static void work_fn(struct work_struct *w)
+{
+	cleanup_old_buffers();
 
-			if (!dm_bufio_trylock(current_client)) {
-				spin_unlock(&global_spinlock);
-				dm_bufio_lock(current_client);
-				locked_client = current_client;
-				continue;
-			}
+	queue_delayed_work(dm_bufio_wq, &dm_bufio_cleanup_old_work,
+			   DM_BUFIO_WORK_TIMER_SECS * HZ);
+}
 
-			locked_client = current_client;
-		}
+/*--------------------------------------------------------------*/
 
-		spin_unlock(&global_spinlock);
+/*
+ * Global cleanup tries to evict the oldest buffers from across _all_
+ * the clients.  It does this by repeatedly evicting a few buffers from
+ * the client that holds the oldest buffer.  It's approximate, but hopefully
+ * good enough.
+ */
+static struct dm_bufio_client *__pop_client(void)
+{
+	struct list_head *h;
 
-		if (unlikely(!__try_evict_buffer(b, GFP_KERNEL))) {
-			spin_lock(&global_spinlock);
-			list_move(&b->global_list, &global_queue);
-			spin_unlock(&global_spinlock);
-		}
+	if (list_empty(&dm_bufio_all_clients))
+		return NULL;
+
+	h = dm_bufio_all_clients.next;
+	list_del(h);
+	return container_of(h, struct dm_bufio_client, client_list);
+}
+
+/*
+ * Inserts the client in the global client list based on its
+ * 'oldest_buffer' field.
+ */
+static void __insert_client(struct dm_bufio_client *new_client)
+{
+	struct dm_bufio_client *c;
+	struct list_head *h = dm_bufio_all_clients.next;
+
+	while (h != &dm_bufio_all_clients) {
+		c = container_of(h, struct dm_bufio_client, client_list);
+		if (time_after_eq(c->oldest_buffer, new_client->oldest_buffer))
+			break;
+		h = h->next;
 	}
 
-	spin_unlock(&global_spinlock);
+	list_add_tail(&new_client->client_list, h);
+}
 
-	if (locked_client)
-		dm_bufio_unlock(locked_client);
+static unsigned long __evict_a_few(unsigned long nr_buffers)
+{
+	unsigned long count;
+	struct dm_bufio_client *c;
+	struct evict_params params = {
+		.gfp = GFP_KERNEL,
+		.age_hz = 0,
+		/* set to jiffies in case there are no buffers in this client */
+		.last_accessed = jiffies
+	};
 
-	mutex_unlock(&dm_bufio_clients_lock);
+	c = __pop_client();
+	if (!c)
+		return 0;
+
+	dm_bufio_lock(c);
+	count = __evict_many(c, &params, LIST_CLEAN, nr_buffers);
+	dm_bufio_unlock(c);
+
+	if (count)
+		c->oldest_buffer = params.last_accessed;
+	__insert_client(c);
+
+	return count;
 }
 
-static void cleanup_old_buffers(void)
+static void check_watermarks(void)
 {
-	unsigned long max_age_hz = get_max_age_hz();
+	LIST_HEAD(write_list);
 	struct dm_bufio_client *c;
 
 	mutex_lock(&dm_bufio_clients_lock);
+	list_for_each_entry(c, &dm_bufio_all_clients, client_list) {
+		dm_bufio_lock(c);
+		__check_watermark(c, &write_list);
+		dm_bufio_unlock(c);
+	}
+	mutex_unlock(&dm_bufio_clients_lock);
 
-	__cache_size_refresh();
+	__flush_write_list(&write_list);
+}
 
-	list_for_each_entry(c, &dm_bufio_all_clients, client_list)
-		__evict_old_buffers(c, max_age_hz);
+static void evict_old(void)
+{
+	unsigned long threshold = dm_bufio_cache_size -
+		dm_bufio_cache_size / DM_BUFIO_LOW_WATERMARK_RATIO;
 
+	mutex_lock(&dm_bufio_clients_lock);
+	while (dm_bufio_current_allocated > threshold) {
+		if (!__evict_a_few(64))
+			break;
+		cond_resched();
+	}
 	mutex_unlock(&dm_bufio_clients_lock);
 }
 
-static void work_fn(struct work_struct *w)
+static void do_global_cleanup(struct work_struct *w)
 {
-	cleanup_old_buffers();
-
-	queue_delayed_work(dm_bufio_wq, &dm_bufio_cleanup_old_work,
-			   DM_BUFIO_WORK_TIMER_SECS * HZ);
+	check_watermarks();
+	evict_old();
 }
 
 /*
@@ -2159,7 +2905,7 @@ static void __exit dm_bufio_exit(void)
 		bug = 1;
 	}
 
-	BUG_ON(bug);
+	WARN_ON(bug); /* leaks are not worth crashing the system */
 }
 
 module_init(dm_bufio_init)