Adding upstream version 6.1.76.upstream/6.1.76

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 2181 insertions, 0 deletions

diff --git a/drivers/md/dm-bufio.c b/drivers/md/dm-bufio.c
new file mode 100644
index 000000000..100a6a236
--- /dev/null
+++ b/drivers/md/dm-bufio.c
@@ -0,0 +1,2181 @@
+/*
+ * Copyright (C) 2009-2011 Red Hat, Inc.
+ *
+ * Author: Mikulas Patocka <mpatocka@redhat.com>
+ *
+ * This file is released under the GPL.
+ */
+
+#include <linux/dm-bufio.h>
+
+#include <linux/device-mapper.h>
+#include <linux/dm-io.h>
+#include <linux/slab.h>
+#include <linux/sched/mm.h>
+#include <linux/jiffies.h>
+#include <linux/vmalloc.h>
+#include <linux/shrinker.h>
+#include <linux/module.h>
+#include <linux/rbtree.h>
+#include <linux/stacktrace.h>
+#include <linux/jump_label.h>
+
+#define DM_MSG_PREFIX "bufio"
+
+/*
+ * Memory management policy:
+ *	Limit the number of buffers to DM_BUFIO_MEMORY_PERCENT of main memory
+ *	or DM_BUFIO_VMALLOC_PERCENT of vmalloc memory (whichever is lower).
+ *	Always allocate at least DM_BUFIO_MIN_BUFFERS buffers.
+ *	Start background writeback when there are DM_BUFIO_WRITEBACK_PERCENT
+ *	dirty buffers.
+ */
+#define DM_BUFIO_MIN_BUFFERS		8
+
+#define DM_BUFIO_MEMORY_PERCENT		2
+#define DM_BUFIO_VMALLOC_PERCENT	25
+#define DM_BUFIO_WRITEBACK_RATIO	3
+#define DM_BUFIO_LOW_WATERMARK_RATIO	16
+
+/*
+ * Check buffer ages in this interval (seconds)
+ */
+#define DM_BUFIO_WORK_TIMER_SECS	30
+
+/*
+ * Free buffers when they are older than this (seconds)
+ */
+#define DM_BUFIO_DEFAULT_AGE_SECS	300
+
+/*
+ * The nr of bytes of cached data to keep around.
+ */
+#define DM_BUFIO_DEFAULT_RETAIN_BYTES   (256 * 1024)
+
+/*
+ * Align buffer writes to this boundary.
+ * Tests show that SSDs have the highest IOPS when using 4k writes.
+ */
+#define DM_BUFIO_WRITE_ALIGN		4096
+
+/*
+ * dm_buffer->list_mode
+ */
+#define LIST_CLEAN	0
+#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.
+ */
+struct dm_bufio_client {
+	struct mutex lock;
+	spinlock_t spinlock;
+	bool no_sleep;
+
+	struct list_head lru[LIST_SIZE];
+	unsigned long n_buffers[LIST_SIZE];
+
+	struct block_device *bdev;
+	unsigned int block_size;
+	s8 sectors_per_block_bits;
+	void (*alloc_callback)(struct dm_buffer *);
+	void (*write_callback)(struct dm_buffer *);
+	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;
+
+	struct rb_root buffer_tree;
+	wait_queue_head_t free_buffer_wait;
+
+	sector_t start;
+
+	int async_write_error;
+
+	struct list_head client_list;
+
+	struct shrinker shrinker;
+	struct work_struct shrink_work;
+	atomic_long_t need_shrink;
+};
+
+/*
+ * Buffer state bits.
+ */
+#define B_READING	0
+#define B_WRITING	1
+#define B_DIRTY		2
+
+/*
+ * Describes how the block was allocated:
+ * kmem_cache_alloc(), __get_free_pages() or vmalloc().
+ * See the comment at alloc_buffer_data.
+ */
+enum data_mode {
+	DATA_MODE_SLAB = 0,
+	DATA_MODE_GET_FREE_PAGES = 1,
+	DATA_MODE_VMALLOC = 2,
+	DATA_MODE_LIMIT = 3
+};
+
+struct dm_buffer {
+	struct rb_node node;
+	struct list_head lru_list;
+	struct list_head global_list;
+	sector_t block;
+	void *data;
+	unsigned char data_mode;		/* DATA_MODE_* */
+	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 *, blk_status_t);
+#ifdef CONFIG_DM_DEBUG_BLOCK_STACK_TRACING
+#define MAX_STACK 10
+	unsigned int stack_len;
+	unsigned long stack_entries[MAX_STACK];
+#endif
+};
+
+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 int dm_bufio_trylock(struct dm_bufio_client *c)
+{
+	if (static_branch_unlikely(&no_sleep_enabled) && c->no_sleep)
+		return spin_trylock_bh(&c->spinlock);
+	else
+		return mutex_trylock(&c->lock);
+}
+
+static void dm_bufio_unlock(struct dm_bufio_client *c)
+{
+	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);
+
+static LIST_HEAD(global_queue);
+
+static unsigned long global_num = 0;
+
+/*
+ * 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
+
+/*----------------------------------------------------------------
+ * A red/black tree acts as an index for all the buffers.
+ *--------------------------------------------------------------*/
+static struct dm_buffer *__find(struct dm_bufio_client *c, sector_t block)
+{
+	struct rb_node *n = c->buffer_tree.rb_node;
+	struct dm_buffer *b;
+
+	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 struct dm_buffer *__find_next(struct dm_bufio_client *c, sector_t block)
+{
+	struct rb_node *n = c->buffer_tree.rb_node;
+	struct dm_buffer *b;
+	struct dm_buffer *best = NULL;
+
+	while (n) {
+		b = container_of(n, struct dm_buffer, node);
+
+		if (b->block == block)
+			return b;
+
+		if (block <= b->block) {
+			n = n->rb_left;
+			best = b;
+		} else {
+			n = n->rb_right;
+		}
+	}
+
+	return best;
+}
+
+static void __insert(struct dm_bufio_client *c, struct dm_buffer *b)
+{
+	struct rb_node **new = &c->buffer_tree.rb_node, *parent = NULL;
+	struct dm_buffer *found;
+
+	while (*new) {
+		found = container_of(*new, struct dm_buffer, node);
+
+		if (found->block == b->block) {
+			BUG_ON(found != b);
+			return;
+		}
+
+		parent = *new;
+		new = b->block < found->block ?
+			&found->node.rb_left : &found->node.rb_right;
+	}
+
+	rb_link_node(&b->node, parent, new);
+	rb_insert_color(&b->node, &c->buffer_tree);
+}
+
+static void __remove(struct dm_bufio_client *c, struct dm_buffer *b)
+{
+	rb_erase(&b->node, &c->buffer_tree);
+}
+
+/*----------------------------------------------------------------*/
+
+static void adjust_total_allocated(struct dm_buffer *b, bool unlink)
+{
+	unsigned char data_mode;
+	long diff;
+
+	static unsigned long * const class_ptr[DATA_MODE_LIMIT] = {
+		&dm_bufio_allocated_kmem_cache,
+		&dm_bufio_allocated_get_free_pages,
+		&dm_bufio_allocated_vmalloc,
+	};
+
+	data_mode = b->data_mode;
+	diff = (long)b->c->block_size;
+	if (unlink)
+		diff = -diff;
+
+	spin_lock(&global_spinlock);
+
+	*class_ptr[data_mode] += diff;
+
+	dm_bufio_current_allocated += diff;
+
+	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);
+}
+
+/*
+ * Change the number of clients and recalculate per-client limit.
+ */
+static void __cache_size_refresh(void)
+{
+	BUG_ON(!mutex_is_locked(&dm_bufio_clients_lock));
+	BUG_ON(dm_bufio_client_count < 0);
+
+	dm_bufio_cache_size_latch = READ_ONCE(dm_bufio_cache_size);
+
+	/*
+	 * Use default if set to 0 and report the actual cache size used.
+	 */
+	if (!dm_bufio_cache_size_latch) {
+		(void)cmpxchg(&dm_bufio_cache_size, 0,
+			      dm_bufio_default_cache_size);
+		dm_bufio_cache_size_latch = dm_bufio_default_cache_size;
+	}
+}
+
+/*
+ * Allocating buffer data.
+ *
+ * Small buffers are allocated with kmem_cache, to use space optimally.
+ *
+ * For large buffers, we choose between get_free_pages and vmalloc.
+ * Each has advantages and disadvantages.
+ *
+ * __get_free_pages can randomly fail if the memory is fragmented.
+ * __vmalloc won't randomly fail, but vmalloc space is limited (it may be
+ * as low as 128M) so using it for caching is not appropriate.
+ *
+ * If the allocation may fail we use __get_free_pages. Memory fragmentation
+ * won't have a fatal effect here, but it just causes flushes of some other
+ * buffers and more I/O will be performed. Don't use __get_free_pages if it
+ * always fails (i.e. order >= MAX_ORDER).
+ *
+ * If the allocation shouldn't fail we use __vmalloc. This is only for the
+ * initial reserve allocation, so there's no risk of wasting all vmalloc
+ * space.
+ */
+static void *alloc_buffer_data(struct dm_bufio_client *c, gfp_t gfp_mask,
+			       unsigned char *data_mode)
+{
+	if (unlikely(c->slab_cache != NULL)) {
+		*data_mode = DATA_MODE_SLAB;
+		return kmem_cache_alloc(c->slab_cache, gfp_mask);
+	}
+
+	if (c->block_size <= KMALLOC_MAX_SIZE &&
+	    gfp_mask & __GFP_NORETRY) {
+		*data_mode = DATA_MODE_GET_FREE_PAGES;
+		return (void *)__get_free_pages(gfp_mask,
+						c->sectors_per_block_bits - (PAGE_SHIFT - SECTOR_SHIFT));
+	}
+
+	*data_mode = DATA_MODE_VMALLOC;
+
+	/*
+	 * __vmalloc allocates the data pages and auxiliary structures with
+	 * gfp_flags that were specified, but pagetables are always allocated
+	 * with GFP_KERNEL, no matter what was specified as gfp_mask.
+	 *
+	 * Consequently, we must set per-process flag PF_MEMALLOC_NOIO so that
+	 * all allocations done by this process (including pagetables) are done
+	 * as if GFP_NOIO was specified.
+	 */
+	if (gfp_mask & __GFP_NORETRY) {
+		unsigned int noio_flag = memalloc_noio_save();
+		void *ptr = __vmalloc(c->block_size, gfp_mask);
+
+		memalloc_noio_restore(noio_flag);
+		return ptr;
+	}
+
+	return __vmalloc(c->block_size, gfp_mask);
+}
+
+/*
+ * Free buffer's data.
+ */
+static void free_buffer_data(struct dm_bufio_client *c,
+			     void *data, unsigned char data_mode)
+{
+	switch (data_mode) {
+	case DATA_MODE_SLAB:
+		kmem_cache_free(c->slab_cache, data);
+		break;
+
+	case DATA_MODE_GET_FREE_PAGES:
+		free_pages((unsigned long)data,
+			   c->sectors_per_block_bits - (PAGE_SHIFT - SECTOR_SHIFT));
+		break;
+
+	case DATA_MODE_VMALLOC:
+		vfree(data);
+		break;
+
+	default:
+		DMCRIT("dm_bufio_free_buffer_data: bad data mode: %d",
+		       data_mode);
+		BUG();
+	}
+}
+
+/*
+ * Allocate buffer and its data.
+ */
+static struct dm_buffer *alloc_buffer(struct dm_bufio_client *c, gfp_t gfp_mask)
+{
+	struct dm_buffer *b = kmem_cache_alloc(c->slab_buffer, gfp_mask);
+
+	if (!b)
+		return NULL;
+
+	b->c = c;
+
+	b->data = alloc_buffer_data(c, gfp_mask, &b->data_mode);
+	if (!b->data) {
+		kmem_cache_free(c->slab_buffer, b);
+		return NULL;
+	}
+
+#ifdef CONFIG_DM_DEBUG_BLOCK_STACK_TRACING
+	b->stack_len = 0;
+#endif
+	return b;
+}
+
+/*
+ * Free buffer and its data.
+ */
+static void free_buffer(struct dm_buffer *b)
+{
+	struct dm_bufio_client *c = b->c;
+
+	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.
+ *
+ * Bio interface is faster but it has some problems:
+ *	the vector list is limited (increasing this limit increases
+ *	memory-consumption per buffer, so it is not viable);
+ *
+ *	the memory must be direct-mapped, not vmalloced;
+ *
+ * If the buffer is small enough (up to DM_BUFIO_INLINE_VECS pages) and
+ * it is not vmalloced, try using the bio interface.
+ *
+ * If the buffer is big, if it is vmalloced or if the underlying device
+ * rejects the bio because it is too large, use dm-io layer to do the I/O.
+ * The dm-io layer splits the I/O into multiple requests, avoiding the above
+ * shortcomings.
+ *--------------------------------------------------------------*/
+
+/*
+ * dm-io completion routine. It just calls b->bio.bi_end_io, pretending
+ * that the request was handled directly with bio interface.
+ */
+static void dmio_complete(unsigned long error, void *context)
+{
+	struct dm_buffer *b = context;
+
+	b->end_io(b, unlikely(error != 0) ? BLK_STS_IOERR : 0);
+}
+
+static void use_dmio(struct dm_buffer *b, enum req_op op, sector_t sector,
+		     unsigned int n_sectors, unsigned int offset)
+{
+	int r;
+	struct dm_io_request io_req = {
+		.bi_opf = op,
+		.notify.fn = dmio_complete,
+		.notify.context = b,
+		.client = b->c->dm_io,
+	};
+	struct dm_io_region region = {
+		.bdev = b->c->bdev,
+		.sector = sector,
+		.count = n_sectors,
+	};
+
+	if (b->data_mode != DATA_MODE_VMALLOC) {
+		io_req.mem.type = DM_IO_KMEM;
+		io_req.mem.ptr.addr = (char *)b->data + offset;
+	} else {
+		io_req.mem.type = DM_IO_VMA;
+		io_req.mem.ptr.vma = (char *)b->data + offset;
+	}
+
+	r = dm_io(&io_req, 1, &region, NULL);
+	if (unlikely(r))
+		b->end_io(b, errno_to_blk_status(r));
+}
+
+static void bio_complete(struct bio *bio)
+{
+	struct dm_buffer *b = bio->bi_private;
+	blk_status_t status = bio->bi_status;
+	bio_uninit(bio);
+	kfree(bio);
+	b->end_io(b, status);
+}
+
+static void use_bio(struct dm_buffer *b, enum req_op op, sector_t sector,
+		    unsigned int n_sectors, unsigned int offset)
+{
+	struct bio *bio;
+	char *ptr;
+	unsigned int vec_size, 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);
+	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->bi_iter.bi_sector = sector;
+	bio->bi_end_io = bio_complete;
+	bio->bi_private = b;
+
+	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);
+
+	submit_bio(bio);
+}
+
+static inline sector_t block_to_sector(struct dm_bufio_client *c, sector_t block)
+{
+	sector_t sector;
+
+	if (likely(c->sectors_per_block_bits >= 0))
+		sector = block << c->sectors_per_block_bits;
+	else
+		sector = block * (c->block_size >> SECTOR_SHIFT);
+	sector += c->start;
+
+	return sector;
+}
+
+static void submit_io(struct dm_buffer *b, enum req_op op,
+		      void (*end_io)(struct dm_buffer *, blk_status_t))
+{
+	unsigned int n_sectors;
+	sector_t sector;
+	unsigned int offset, end;
+
+	b->end_io = end_io;
+
+	sector = block_to_sector(b->c, b->block);
+
+	if (op != REQ_OP_WRITE) {
+		n_sectors = b->c->block_size >> SECTOR_SHIFT;
+		offset = 0;
+	} else {
+		if (b->c->write_callback)
+			b->c->write_callback(b);
+		offset = b->write_start;
+		end = b->write_end;
+		offset &= -DM_BUFIO_WRITE_ALIGN;
+		end += DM_BUFIO_WRITE_ALIGN - 1;
+		end &= -DM_BUFIO_WRITE_ALIGN;
+		if (unlikely(end > b->c->block_size))
+			end = b->c->block_size;
+
+		sector += offset >> SECTOR_SHIFT;
+		n_sectors = (end - offset) >> SECTOR_SHIFT;
+	}
+
+	if (b->data_mode != DATA_MODE_VMALLOC)
+		use_bio(b, op, sector, n_sectors, offset);
+	else
+		use_dmio(b, op, sector, n_sectors, offset);
+}
+
+/*----------------------------------------------------------------
+ * Writing dirty buffers
+ *--------------------------------------------------------------*/
+
+/*
+ * The endio routine for write.
+ *
+ * Set the error, clear B_WRITING bit and wake anyone who was waiting on
+ * it.
+ */
+static void write_endio(struct dm_buffer *b, blk_status_t status)
+{
+	b->write_error = status;
+	if (unlikely(status)) {
+		struct dm_bufio_client *c = b->c;
+
+		(void)cmpxchg(&c->async_write_error, 0,
+				blk_status_to_errno(status));
+	}
+
+	BUG_ON(!test_bit(B_WRITING, &b->state));
+
+	smp_mb__before_atomic();
+	clear_bit(B_WRITING, &b->state);
+	smp_mb__after_atomic();
+
+	wake_up_bit(&b->state, B_WRITING);
+}
+
+/*
+ * Initiate a write on a dirty buffer, but don't wait for it.
+ *
+ * - If the buffer is not dirty, exit.
+ * - If there some previous write going on, wait for it to finish (we can't
+ *   have two writes on the same buffer simultaneously).
+ * - Submit our write and don't wait on it. We set B_WRITING indicating
+ *   that there is a write in progress.
+ */
+static void __write_dirty_buffer(struct dm_buffer *b,
+				 struct list_head *write_list)
+{
+	if (!test_bit(B_DIRTY, &b->state))
+		return;
+
+	clear_bit(B_DIRTY, &b->state);
+	wait_on_bit_lock_io(&b->state, B_WRITING, TASK_UNINTERRUPTIBLE);
+
+	b->write_start = b->dirty_start;
+	b->write_end = b->dirty_end;
+
+	if (!write_list)
+		submit_io(b, REQ_OP_WRITE, write_endio);
+	else
+		list_add_tail(&b->write_list, write_list);
+}
+
+static void __flush_write_list(struct list_head *write_list)
+{
+	struct blk_plug plug;
+	blk_start_plug(&plug);
+	while (!list_empty(write_list)) {
+		struct dm_buffer *b =
+			list_entry(write_list->next, struct dm_buffer, write_list);
+		list_del(&b->write_list);
+		submit_io(b, REQ_OP_WRITE, write_endio);
+		cond_resched();
+	}
+	blk_finish_plug(&plug);
+}
+
+/*
+ * Wait until any activity on the buffer finishes.  Possibly write the
+ * buffer if it is dirty.  When this function finishes, there is no I/O
+ * running on the buffer and the buffer is not dirty.
+ */
+static void __make_buffer_clean(struct dm_buffer *b)
+{
+	BUG_ON(b->hold_count);
+
+	/* smp_load_acquire() pairs with read_endio()'s smp_mb__before_atomic() */
+	if (!smp_load_acquire(&b->state))	/* fast case */
+		return;
+
+	wait_on_bit_io(&b->state, B_READING, TASK_UNINTERRUPTIBLE);
+	__write_dirty_buffer(b, NULL);
+	wait_on_bit_io(&b->state, B_WRITING, TASK_UNINTERRUPTIBLE);
+}
+
+/*
+ * Find some buffer that is not held by anybody, clean it, unlink it and
+ * return it.
+ */
+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();
+	}
+
+	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();
+	}
+
+	return NULL;
+}
+
+/*
+ * Wait until some other threads free some buffer or release hold count on
+ * some buffer.
+ *
+ * This function is entered with c->lock held, drops it and regains it
+ * before exiting.
+ */
+static void __wait_for_free_buffer(struct dm_bufio_client *c)
+{
+	DECLARE_WAITQUEUE(wait, current);
+
+	add_wait_queue(&c->free_buffer_wait, &wait);
+	set_current_state(TASK_UNINTERRUPTIBLE);
+	dm_bufio_unlock(c);
+
+	io_schedule();
+
+	remove_wait_queue(&c->free_buffer_wait, &wait);
+
+	dm_bufio_lock(c);
+}
+
+enum new_flag {
+	NF_FRESH = 0,
+	NF_READ = 1,
+	NF_GET = 2,
+	NF_PREFETCH = 3
+};
+
+/*
+ * Allocate a new buffer. If the allocation is not possible, wait until
+ * some other thread frees a buffer.
+ *
+ * May drop the lock and regain it.
+ */
+static struct dm_buffer *__alloc_buffer_wait_no_callback(struct dm_bufio_client *c, enum new_flag nf)
+{
+	struct dm_buffer *b;
+	bool tried_noio_alloc = false;
+
+	/*
+	 * dm-bufio is resistant to allocation failures (it just keeps
+	 * one buffer reserved in cases all the allocations fail).
+	 * So set flags to not try too hard:
+	 *	GFP_NOWAIT: don't wait; if we need to sleep we'll release our
+	 *		    mutex and wait ourselves.
+	 *	__GFP_NORETRY: don't retry and rather return failure
+	 *	__GFP_NOMEMALLOC: don't use emergency reserves
+	 *	__GFP_NOWARN: don't print a warning in case of failure
+	 *
+	 * For debugging, if we set the cache size to 1, no new buffers will
+	 * be allocated.
+	 */
+	while (1) {
+		if (dm_bufio_cache_size_latch != 1) {
+			b = alloc_buffer(c, GFP_NOWAIT | __GFP_NORETRY | __GFP_NOMEMALLOC | __GFP_NOWARN);
+			if (b)
+				return b;
+		}
+
+		if (nf == NF_PREFETCH)
+			return NULL;
+
+		if (dm_bufio_cache_size_latch != 1 && !tried_noio_alloc) {
+			dm_bufio_unlock(c);
+			b = alloc_buffer(c, GFP_NOIO | __GFP_NORETRY | __GFP_NOMEMALLOC | __GFP_NOWARN);
+			dm_bufio_lock(c);
+			if (b)
+				return b;
+			tried_noio_alloc = true;
+		}
+
+		if (!list_empty(&c->reserved_buffers)) {
+			b = list_entry(c->reserved_buffers.next,
+				       struct dm_buffer, lru_list);
+			list_del(&b->lru_list);
+			c->need_reserved_buffers++;
+
+			return b;
+		}
+
+		b = __get_unclaimed_buffer(c);
+		if (b)
+			return b;
+
+		__wait_for_free_buffer(c);
+	}
+}
+
+static struct dm_buffer *__alloc_buffer_wait(struct dm_bufio_client *c, enum new_flag nf)
+{
+	struct dm_buffer *b = __alloc_buffer_wait_no_callback(c, nf);
+
+	if (!b)
+		return NULL;
+
+	if (c->alloc_callback)
+		c->alloc_callback(b);
+
+	return b;
+}
+
+/*
+ * Free a buffer and wake other threads waiting for free buffers.
+ */
+static void __free_buffer_wake(struct dm_buffer *b)
+{
+	struct dm_bufio_client *c = b->c;
+
+	if (!c->need_reserved_buffers)
+		free_buffer(b);
+	else {
+		list_add(&b->lru_list, &c->reserved_buffers);
+		c->need_reserved_buffers--;
+	}
+
+	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)
+{
+	struct dm_buffer *b, *tmp;
+
+	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)) {
+			__relink_lru(b, LIST_CLEAN);
+			continue;
+		}
+
+		if (no_wait && test_bit(B_WRITING, &b->state))
+			return;
+
+		__write_dirty_buffer(b, write_list);
+		cond_resched();
+	}
+}
+
+/*
+ * Check if we're over watermark.
+ * If we are over threshold_buffers, start freeing buffers.
+ * If we're over "limit_buffers", block until we get under the limit.
+ */
+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)
+		__write_dirty_buffers_async(c, 1, write_list);
+}
+
+/*----------------------------------------------------------------
+ * Getting a buffer
+ *--------------------------------------------------------------*/
+
+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)
+{
+	struct dm_buffer *b, *new_b = NULL;
+
+	*need_submit = 0;
+
+	b = __find(c, block);
+	if (b)
+		goto found_buffer;
+
+	if (nf == NF_GET)
+		return NULL;
+
+	new_b = __alloc_buffer_wait(c, nf);
+	if (!new_b)
+		return NULL;
+
+	/*
+	 * We've had a period where the mutex was unlocked, so need to
+	 * recheck the buffer tree.
+	 */
+	b = __find(c, block);
+	if (b) {
+		__free_buffer_wake(new_b);
+		goto found_buffer;
+	}
+
+	__check_watermark(c, write_list);
+
+	b = new_b;
+	b->hold_count = 1;
+	b->read_error = 0;
+	b->write_error = 0;
+	__link_buffer(b, block, LIST_CLEAN);
+
+	if (nf == NF_FRESH) {
+		b->state = 0;
+		return b;
+	}
+
+	b->state = 1 << B_READING;
+	*need_submit = 1;
+
+	return b;
+
+found_buffer:
+	if (nf == NF_PREFETCH)
+		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)))
+		return NULL;
+
+	b->hold_count++;
+	__relink_lru(b, test_bit(B_DIRTY, &b->state) ||
+		     test_bit(B_WRITING, &b->state));
+	return b;
+}
+
+/*
+ * The endio routine for reading: set the error, clear the bit and wake up
+ * anyone waiting on the buffer.
+ */
+static void read_endio(struct dm_buffer *b, blk_status_t status)
+{
+	b->read_error = status;
+
+	BUG_ON(!test_bit(B_READING, &b->state));
+
+	smp_mb__before_atomic();
+	clear_bit(B_READING, &b->state);
+	smp_mb__after_atomic();
+
+	wake_up_bit(&b->state, B_READING);
+}
+
+/*
+ * A common routine for dm_bufio_new and dm_bufio_read.  Operation of these
+ * functions is similar except that dm_bufio_new doesn't read the
+ * buffer from the disk (assuming that the caller overwrites all the data
+ * and uses dm_bufio_mark_buffer_dirty to write new data back).
+ */
+static void *new_read(struct dm_bufio_client *c, sector_t block,
+		      enum new_flag nf, struct dm_buffer **bp)
+{
+	int need_submit;
+	struct dm_buffer *b;
+
+	LIST_HEAD(write_list);
+
+	dm_bufio_lock(c);
+	b = __bufio_new(c, block, nf, &need_submit, &write_list);
+#ifdef CONFIG_DM_DEBUG_BLOCK_STACK_TRACING
+	if (b && b->hold_count == 1)
+		buffer_record_stack(b);
+#endif
+	dm_bufio_unlock(c);
+
+	__flush_write_list(&write_list);
+
+	if (!b)
+		return NULL;
+
+	if (need_submit)
+		submit_io(b, REQ_OP_READ, read_endio);
+
+	wait_on_bit_io(&b->state, B_READING, TASK_UNINTERRUPTIBLE);
+
+	if (b->read_error) {
+		int error = blk_status_to_errno(b->read_error);
+
+		dm_bufio_release(b);
+
+		return ERR_PTR(error);
+	}
+
+	*bp = b;
+
+	return b->data;
+}
+
+void *dm_bufio_get(struct dm_bufio_client *c, sector_t block,
+		   struct dm_buffer **bp)
+{
+	return new_read(c, block, NF_GET, bp);
+}
+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());
+
+	return new_read(c, block, NF_READ, bp);
+}
+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());
+
+	return new_read(c, block, NF_FRESH, bp);
+}
+EXPORT_SYMBOL_GPL(dm_bufio_new);
+
+void dm_bufio_prefetch(struct dm_bufio_client *c,
+		       sector_t block, unsigned int n_blocks)
+{
+	struct blk_plug plug;
+
+	LIST_HEAD(write_list);
+
+	BUG_ON(dm_bufio_in_request());
+
+	blk_start_plug(&plug);
+	dm_bufio_lock(c);
+
+	for (; n_blocks--; block++) {
+		int need_submit;
+		struct dm_buffer *b;
+		b = __bufio_new(c, block, NF_PREFETCH, &need_submit,
+				&write_list);
+		if (unlikely(!list_empty(&write_list))) {
+			dm_bufio_unlock(c);
+			blk_finish_plug(&plug);
+			__flush_write_list(&write_list);
+			blk_start_plug(&plug);
+			dm_bufio_lock(c);
+		}
+		if (unlikely(b != NULL)) {
+			dm_bufio_unlock(c);
+
+			if (need_submit)
+				submit_io(b, REQ_OP_READ, read_endio);
+			dm_bufio_release(b);
+
+			cond_resched();
+
+			if (!n_blocks)
+				goto flush_plug;
+			dm_bufio_lock(c);
+		}
+	}
+
+	dm_bufio_unlock(c);
+
+flush_plug:
+	blk_finish_plug(&plug);
+}
+EXPORT_SYMBOL_GPL(dm_bufio_prefetch);
+
+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)) {
+			__unlink_buffer(b);
+			__free_buffer_wake(b);
+		}
+	}
+
+	dm_bufio_unlock(c);
+}
+EXPORT_SYMBOL_GPL(dm_bufio_release);
+
+void dm_bufio_mark_partial_buffer_dirty(struct dm_buffer *b,
+					unsigned int start, unsigned int end)
+{
+	struct dm_bufio_client *c = b->c;
+
+	BUG_ON(start >= end);
+	BUG_ON(end > b->c->block_size);
+
+	dm_bufio_lock(c);
+
+	BUG_ON(test_bit(B_READING, &b->state));
+
+	if (!test_and_set_bit(B_DIRTY, &b->state)) {
+		b->dirty_start = start;
+		b->dirty_end = end;
+		__relink_lru(b, LIST_DIRTY);
+	} else {
+		if (start < b->dirty_start)
+			b->dirty_start = start;
+		if (end > b->dirty_end)
+			b->dirty_end = end;
+	}
+
+	dm_bufio_unlock(c);
+}
+EXPORT_SYMBOL_GPL(dm_bufio_mark_partial_buffer_dirty);
+
+void dm_bufio_mark_buffer_dirty(struct dm_buffer *b)
+{
+	dm_bufio_mark_partial_buffer_dirty(b, 0, b->c->block_size);
+}
+EXPORT_SYMBOL_GPL(dm_bufio_mark_buffer_dirty);
+
+void dm_bufio_write_dirty_buffers_async(struct dm_bufio_client *c)
+{
+	LIST_HEAD(write_list);
+
+	BUG_ON(dm_bufio_in_request());
+
+	dm_bufio_lock(c);
+	__write_dirty_buffers_async(c, 0, &write_list);
+	dm_bufio_unlock(c);
+	__flush_write_list(&write_list);
+}
+EXPORT_SYMBOL_GPL(dm_bufio_write_dirty_buffers_async);
+
+/*
+ * For performance, it is essential that the buffers are written asynchronously
+ * and simultaneously (so that the block layer can merge the writes) and then
+ * waited upon.
+ *
+ * Finally, we flush hardware disk cache.
+ */
+int dm_bufio_write_dirty_buffers(struct dm_bufio_client *c)
+{
+	int a, f;
+	unsigned long buffers_processed = 0;
+	struct dm_buffer *b, *tmp;
+
+	LIST_HEAD(write_list);
+
+	dm_bufio_lock(c);
+	__write_dirty_buffers_async(c, 0, &write_list);
+	dm_bufio_unlock(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++;
+
+		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 (!test_bit(B_DIRTY, &b->state) &&
+		    !test_bit(B_WRITING, &b->state))
+			__relink_lru(b, LIST_CLEAN);
+
+		cond_resched();
+
+		/*
+		 * 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;
+	}
+	wake_up(&c->free_buffer_wait);
+	dm_bufio_unlock(c);
+
+	a = xchg(&c->async_write_error, 0);
+	f = dm_bufio_issue_flush(c);
+	if (a)
+		return a;
+
+	return f;
+}
+EXPORT_SYMBOL_GPL(dm_bufio_write_dirty_buffers);
+
+/*
+ * Use dm-io to send an empty barrier to flush the device.
+ */
+int dm_bufio_issue_flush(struct dm_bufio_client *c)
+{
+	struct dm_io_request io_req = {
+		.bi_opf = REQ_OP_WRITE | REQ_PREFLUSH | REQ_SYNC,
+		.mem.type = DM_IO_KMEM,
+		.mem.ptr.addr = NULL,
+		.client = c->dm_io,
+	};
+	struct dm_io_region io_reg = {
+		.bdev = c->bdev,
+		.sector = 0,
+		.count = 0,
+	};
+
+	BUG_ON(dm_bufio_in_request());
+
+	return dm_io(&io_req, 1, &io_reg, NULL);
+}
+EXPORT_SYMBOL_GPL(dm_bufio_issue_flush);
+
+/*
+ * Use dm-io to send a discard request to flush the device.
+ */
+int dm_bufio_issue_discard(struct dm_bufio_client *c, sector_t block, sector_t count)
+{
+	struct dm_io_request io_req = {
+		.bi_opf = REQ_OP_DISCARD | REQ_SYNC,
+		.mem.type = DM_IO_KMEM,
+		.mem.ptr.addr = NULL,
+		.client = c->dm_io,
+	};
+	struct dm_io_region io_reg = {
+		.bdev = c->bdev,
+		.sector = block_to_sector(c, block),
+		.count = block_to_sector(c, count),
+	};
+
+	BUG_ON(dm_bufio_in_request());
+
+	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)
+{
+	struct dm_bufio_client *c = b->c;
+	struct dm_buffer *new;
+
+	BUG_ON(dm_bufio_in_request());
+
+	dm_bufio_lock(c);
+
+retry:
+	new = __find(c, new_block);
+	if (new) {
+		if (new->hold_count) {
+			__wait_for_free_buffer(c);
+			goto retry;
+		}
+
+		/*
+		 * 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);
+	}
+}
+
+/*
+ * Free the given buffer.
+ *
+ * This is just a hint, if the buffer is in use or dirty, this function
+ * does nothing.
+ */
+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);
+
+	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)
+{
+	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;
+	}
+
+}
+EXPORT_SYMBOL_GPL(dm_bufio_forget_buffers);
+
+void dm_bufio_set_minimum_buffers(struct dm_bufio_client *c, unsigned int n)
+{
+	c->minimum_buffers = n;
+}
+EXPORT_SYMBOL_GPL(dm_bufio_set_minimum_buffers);
+
+unsigned int dm_bufio_get_block_size(struct dm_bufio_client *c)
+{
+	return c->block_size;
+}
+EXPORT_SYMBOL_GPL(dm_bufio_get_block_size);
+
+sector_t dm_bufio_get_device_size(struct dm_bufio_client *c)
+{
+	sector_t s = bdev_nr_sectors(c->bdev);
+	if (s >= c->start)
+		s -= c->start;
+	else
+		s = 0;
+	if (likely(c->sectors_per_block_bits >= 0))
+		s >>= c->sectors_per_block_bits;
+	else
+		sector_div(s, c->block_size >> SECTOR_SHIFT);
+	return s;
+}
+EXPORT_SYMBOL_GPL(dm_bufio_get_device_size);
+
+struct dm_io_client *dm_bufio_get_dm_io_client(struct dm_bufio_client *c)
+{
+	return c->dm_io;
+}
+EXPORT_SYMBOL_GPL(dm_bufio_get_dm_io_client);
+
+sector_t dm_bufio_get_block_number(struct dm_buffer *b)
+{
+	return b->block;
+}
+EXPORT_SYMBOL_GPL(dm_bufio_get_block_number);
+
+void *dm_bufio_get_block_data(struct dm_buffer *b)
+{
+	return b->data;
+}
+EXPORT_SYMBOL_GPL(dm_bufio_get_block_data);
+
+void *dm_bufio_get_aux_data(struct dm_buffer *b)
+{
+	return b + 1;
+}
+EXPORT_SYMBOL_GPL(dm_bufio_get_aux_data);
+
+struct dm_bufio_client *dm_bufio_get_client(struct dm_buffer *b)
+{
+	return b->c;
+}
+EXPORT_SYMBOL_GPL(dm_bufio_get_client);
+
+static void drop_buffers(struct dm_bufio_client *c)
+{
+	struct dm_buffer *b;
+	int i;
+	bool warned = false;
+
+	BUG_ON(dm_bufio_in_request());
+
+	/*
+	 * An optimization so that the buffers are not written one-by-one.
+	 */
+	dm_bufio_write_dirty_buffers_async(c);
+
+	dm_bufio_lock(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
+		}
+
+#ifdef CONFIG_DM_DEBUG_BLOCK_STACK_TRACING
+	while ((b = __get_unclaimed_buffer(c)))
+		__free_buffer_wake(b);
+#endif
+
+	for (i = 0; i < LIST_SIZE; i++)
+		BUG_ON(!list_empty(&c->lru[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);
+	if (likely(c->sectors_per_block_bits >= 0))
+		retain_bytes >>= c->sectors_per_block_bits + SECTOR_SHIFT;
+	else
+		retain_bytes /= c->block_size;
+	return retain_bytes;
+}
+
+static void __scan(struct dm_bufio_client *c)
+{
+	int l;
+	struct dm_buffer *b, *tmp;
+	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);
+
+	for (l = 0; l < LIST_SIZE; l++) {
+		list_for_each_entry_safe_reverse(b, tmp, &c->lru[l], lru_list) {
+			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++;
+			}
+			cond_resched();
+		}
+	}
+}
+
+static void shrink_work(struct work_struct *w)
+{
+	struct dm_bufio_client *c = container_of(w, struct dm_bufio_client, shrink_work);
+
+	dm_bufio_lock(c);
+	__scan(c);
+	dm_bufio_unlock(c);
+}
+
+static unsigned long dm_bufio_shrink_scan(struct shrinker *shrink, struct shrink_control *sc)
+{
+	struct dm_bufio_client *c;
+
+	c = container_of(shrink, struct dm_bufio_client, shrinker);
+	atomic_long_add(sc->nr_to_scan, &c->need_shrink);
+	queue_work(dm_bufio_wq, &c->shrink_work);
+
+	return sc->nr_to_scan;
+}
+
+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 retain_target = get_retain_buffers(c);
+	unsigned long queued_for_cleanup = atomic_long_read(&c->need_shrink);
+
+	if (unlikely(count < retain_target))
+		count = 0;
+	else
+		count -= retain_target;
+
+	if (unlikely(count < queued_for_cleanup))
+		count = 0;
+	else
+		count -= queued_for_cleanup;
+
+	return count;
+}
+
+/*
+ * Create the buffering interface
+ */
+struct dm_bufio_client *dm_bufio_client_create(struct block_device *bdev, unsigned int block_size,
+					       unsigned int reserved_buffers, unsigned int aux_size,
+					       void (*alloc_callback)(struct dm_buffer *),
+					       void (*write_callback)(struct dm_buffer *),
+					       unsigned int flags)
+{
+	int r;
+	struct dm_bufio_client *c;
+	unsigned int i;
+	char slab_name[27];
+
+	if (!block_size || block_size & ((1 << SECTOR_SHIFT) - 1)) {
+		DMERR("%s: block size not specified or is not multiple of 512b", __func__);
+		r = -EINVAL;
+		goto bad_client;
+	}
+
+	c = kzalloc(sizeof(*c), GFP_KERNEL);
+	if (!c) {
+		r = -ENOMEM;
+		goto bad_client;
+	}
+	c->buffer_tree = RB_ROOT;
+
+	c->bdev = bdev;
+	c->block_size = block_size;
+	if (is_power_of_2(block_size))
+		c->sectors_per_block_bits = __ffs(block_size) - SECTOR_SHIFT;
+	else
+		c->sectors_per_block_bits = -1;
+
+	c->alloc_callback = alloc_callback;
+	c->write_callback = write_callback;
+
+	if (flags & DM_BUFIO_CLIENT_NO_SLEEP) {
+		c->no_sleep = true;
+		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);
+	c->need_reserved_buffers = reserved_buffers;
+
+	dm_bufio_set_minimum_buffers(c, DM_BUFIO_MIN_BUFFERS);
+
+	init_waitqueue_head(&c->free_buffer_wait);
+	c->async_write_error = 0;
+
+	c->dm_io = dm_io_client_create();
+	if (IS_ERR(c->dm_io)) {
+		r = PTR_ERR(c->dm_io);
+		goto bad_dm_io;
+	}
+
+	if (block_size <= KMALLOC_MAX_SIZE &&
+	    (block_size < PAGE_SIZE || !is_power_of_2(block_size))) {
+		unsigned int align = min(1U << __ffs(block_size), (unsigned int)PAGE_SIZE);
+		snprintf(slab_name, sizeof slab_name, "dm_bufio_cache-%u", block_size);
+		c->slab_cache = kmem_cache_create(slab_name, block_size, align,
+						  SLAB_RECLAIM_ACCOUNT, NULL);
+		if (!c->slab_cache) {
+			r = -ENOMEM;
+			goto bad;
+		}
+	}
+	if (aux_size)
+		snprintf(slab_name, sizeof slab_name, "dm_bufio_buffer-%u", aux_size);
+	else
+		snprintf(slab_name, sizeof slab_name, "dm_bufio_buffer");
+	c->slab_buffer = kmem_cache_create(slab_name, sizeof(struct dm_buffer) + aux_size,
+					   0, SLAB_RECLAIM_ACCOUNT, NULL);
+	if (!c->slab_buffer) {
+		r = -ENOMEM;
+		goto bad;
+	}
+
+	while (c->need_reserved_buffers) {
+		struct dm_buffer *b = alloc_buffer(c, GFP_KERNEL);
+
+		if (!b) {
+			r = -ENOMEM;
+			goto bad;
+		}
+		__free_buffer_wake(b);
+	}
+
+	INIT_WORK(&c->shrink_work, shrink_work);
+	atomic_long_set(&c->need_shrink, 0);
+
+	c->shrinker.count_objects = dm_bufio_shrink_count;
+	c->shrinker.scan_objects = dm_bufio_shrink_scan;
+	c->shrinker.seeks = 1;
+	c->shrinker.batch = 0;
+	r = register_shrinker(&c->shrinker, "dm-bufio:(%u:%u)",
+			      MAJOR(bdev->bd_dev), MINOR(bdev->bd_dev));
+	if (r)
+		goto bad;
+
+	mutex_lock(&dm_bufio_clients_lock);
+	dm_bufio_client_count++;
+	list_add(&c->client_list, &dm_bufio_all_clients);
+	__cache_size_refresh();
+	mutex_unlock(&dm_bufio_clients_lock);
+
+	return c;
+
+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);
+		free_buffer(b);
+	}
+	kmem_cache_destroy(c->slab_cache);
+	kmem_cache_destroy(c->slab_buffer);
+	dm_io_client_destroy(c->dm_io);
+bad_dm_io:
+	mutex_destroy(&c->lock);
+	if (c->no_sleep)
+		static_branch_dec(&no_sleep_enabled);
+	kfree(c);
+bad_client:
+	return ERR_PTR(r);
+}
+EXPORT_SYMBOL_GPL(dm_bufio_client_create);
+
+/*
+ * Free the buffering interface.
+ * It is required that there are no references on any buffers.
+ */
+void dm_bufio_client_destroy(struct dm_bufio_client *c)
+{
+	unsigned int i;
+
+	drop_buffers(c);
+
+	unregister_shrinker(&c->shrinker);
+	flush_work(&c->shrink_work);
+
+	mutex_lock(&dm_bufio_clients_lock);
+
+	list_del(&c->client_list);
+	dm_bufio_client_count--;
+	__cache_size_refresh();
+
+	mutex_unlock(&dm_bufio_clients_lock);
+
+	BUG_ON(!RB_EMPTY_ROOT(&c->buffer_tree));
+	BUG_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);
+		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]);
+
+	for (i = 0; i < LIST_SIZE; i++)
+		BUG_ON(c->n_buffers[i]);
+
+	kmem_cache_destroy(c->slab_cache);
+	kmem_cache_destroy(c->slab_buffer);
+	dm_io_client_destroy(c->dm_io);
+	mutex_destroy(&c->lock);
+	if (c->no_sleep)
+		static_branch_dec(&no_sleep_enabled);
+	kfree(c);
+}
+EXPORT_SYMBOL_GPL(dm_bufio_client_destroy);
+
+void dm_bufio_client_reset(struct dm_bufio_client *c)
+{
+	drop_buffers(c);
+	flush_work(&c->shrink_work);
+}
+EXPORT_SYMBOL_GPL(dm_bufio_client_reset);
+
+void dm_bufio_set_sector_offset(struct dm_bufio_client *c, sector_t start)
+{
+	c->start = 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);
+
+	if (max_age > UINT_MAX / HZ)
+		max_age = UINT_MAX / HZ;
+
+	return max_age * HZ;
+}
+
+static bool older_than(struct dm_buffer *b, unsigned long age_hz)
+{
+	return time_after_eq(jiffies, b->last_accessed + age_hz);
+}
+
+static void __evict_old_buffers(struct dm_bufio_client *c, unsigned long age_hz)
+{
+	struct dm_buffer *b, *tmp;
+	unsigned long retain_target = get_retain_buffers(c);
+	unsigned long count;
+	LIST_HEAD(write_list);
+
+	dm_bufio_lock(c);
+
+	__check_watermark(c, &write_list);
+	if (unlikely(!list_empty(&write_list))) {
+		dm_bufio_unlock(c);
+		__flush_write_list(&write_list);
+		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();
+	}
+
+	dm_bufio_unlock(c);
+}
+
+static void do_global_cleanup(struct work_struct *w)
+{
+	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;
+
+	mutex_lock(&dm_bufio_clients_lock);
+
+	while (1) {
+		cond_resched();
+
+		spin_lock(&global_spinlock);
+		if (unlikely(dm_bufio_current_allocated <= threshold))
+			break;
+
+		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;
+		}
+
+		current_client = b->c;
+		if (unlikely(current_client != locked_client)) {
+			if (locked_client)
+				dm_bufio_unlock(locked_client);
+
+			if (!dm_bufio_trylock(current_client)) {
+				spin_unlock(&global_spinlock);
+				dm_bufio_lock(current_client);
+				locked_client = current_client;
+				continue;
+			}
+
+			locked_client = current_client;
+		}
+
+		spin_unlock(&global_spinlock);
+
+		if (unlikely(!__try_evict_buffer(b, GFP_KERNEL))) {
+			spin_lock(&global_spinlock);
+			list_move(&b->global_list, &global_queue);
+			spin_unlock(&global_spinlock);
+		}
+	}
+
+	spin_unlock(&global_spinlock);
+
+	if (locked_client)
+		dm_bufio_unlock(locked_client);
+
+	mutex_unlock(&dm_bufio_clients_lock);
+}
+
+static void cleanup_old_buffers(void)
+{
+	unsigned long max_age_hz = get_max_age_hz();
+	struct dm_bufio_client *c;
+
+	mutex_lock(&dm_bufio_clients_lock);
+
+	__cache_size_refresh();
+
+	list_for_each_entry(c, &dm_bufio_all_clients, client_list)
+		__evict_old_buffers(c, max_age_hz);
+
+	mutex_unlock(&dm_bufio_clients_lock);
+}
+
+static void work_fn(struct work_struct *w)
+{
+	cleanup_old_buffers();
+
+	queue_delayed_work(dm_bufio_wq, &dm_bufio_cleanup_old_work,
+			   DM_BUFIO_WORK_TIMER_SECS * HZ);
+}
+
+/*----------------------------------------------------------------
+ * Module setup
+ *--------------------------------------------------------------*/
+
+/*
+ * This is called only once for the whole dm_bufio module.
+ * It initializes memory limit.
+ */
+static int __init dm_bufio_init(void)
+{
+	__u64 mem;
+
+	dm_bufio_allocated_kmem_cache = 0;
+	dm_bufio_allocated_get_free_pages = 0;
+	dm_bufio_allocated_vmalloc = 0;
+	dm_bufio_current_allocated = 0;
+
+	mem = (__u64)mult_frac(totalram_pages() - totalhigh_pages(),
+			       DM_BUFIO_MEMORY_PERCENT, 100) << PAGE_SHIFT;
+
+	if (mem > ULONG_MAX)
+		mem = ULONG_MAX;
+
+#ifdef CONFIG_MMU
+	if (mem > mult_frac(VMALLOC_TOTAL, DM_BUFIO_VMALLOC_PERCENT, 100))
+		mem = mult_frac(VMALLOC_TOTAL, DM_BUFIO_VMALLOC_PERCENT, 100);
+#endif
+
+	dm_bufio_default_cache_size = mem;
+
+	mutex_lock(&dm_bufio_clients_lock);
+	__cache_size_refresh();
+	mutex_unlock(&dm_bufio_clients_lock);
+
+	dm_bufio_wq = alloc_workqueue("dm_bufio_cache", WQ_MEM_RECLAIM, 0);
+	if (!dm_bufio_wq)
+		return -ENOMEM;
+
+	INIT_DELAYED_WORK(&dm_bufio_cleanup_old_work, work_fn);
+	INIT_WORK(&dm_bufio_replacement_work, do_global_cleanup);
+	queue_delayed_work(dm_bufio_wq, &dm_bufio_cleanup_old_work,
+			   DM_BUFIO_WORK_TIMER_SECS * HZ);
+
+	return 0;
+}
+
+/*
+ * This is called once when unloading the dm_bufio module.
+ */
+static void __exit dm_bufio_exit(void)
+{
+	int bug = 0;
+
+	cancel_delayed_work_sync(&dm_bufio_cleanup_old_work);
+	destroy_workqueue(dm_bufio_wq);
+
+	if (dm_bufio_client_count) {
+		DMCRIT("%s: dm_bufio_client_count leaked: %d",
+			__func__, dm_bufio_client_count);
+		bug = 1;
+	}
+
+	if (dm_bufio_current_allocated) {
+		DMCRIT("%s: dm_bufio_current_allocated leaked: %lu",
+			__func__, dm_bufio_current_allocated);
+		bug = 1;
+	}
+
+	if (dm_bufio_allocated_get_free_pages) {
+		DMCRIT("%s: dm_bufio_allocated_get_free_pages leaked: %lu",
+		       __func__, dm_bufio_allocated_get_free_pages);
+		bug = 1;
+	}
+
+	if (dm_bufio_allocated_vmalloc) {
+		DMCRIT("%s: dm_bufio_vmalloc leaked: %lu",
+		       __func__, dm_bufio_allocated_vmalloc);
+		bug = 1;
+	}
+
+	BUG_ON(bug);
+}
+
+module_init(dm_bufio_init)
+module_exit(dm_bufio_exit)
+
+module_param_named(max_cache_size_bytes, dm_bufio_cache_size, ulong, S_IRUGO | S_IWUSR);
+MODULE_PARM_DESC(max_cache_size_bytes, "Size of metadata cache");
+
+module_param_named(max_age_seconds, dm_bufio_max_age, uint, S_IRUGO | S_IWUSR);
+MODULE_PARM_DESC(max_age_seconds, "Max age of a buffer in seconds");
+
+module_param_named(retain_bytes, dm_bufio_retain_bytes, ulong, S_IRUGO | S_IWUSR);
+MODULE_PARM_DESC(retain_bytes, "Try to keep at least this many bytes cached in memory");
+
+module_param_named(peak_allocated_bytes, dm_bufio_peak_allocated, ulong, S_IRUGO | S_IWUSR);
+MODULE_PARM_DESC(peak_allocated_bytes, "Tracks the maximum allocated memory");
+
+module_param_named(allocated_kmem_cache_bytes, dm_bufio_allocated_kmem_cache, ulong, S_IRUGO);
+MODULE_PARM_DESC(allocated_kmem_cache_bytes, "Memory allocated with kmem_cache_alloc");
+
+module_param_named(allocated_get_free_pages_bytes, dm_bufio_allocated_get_free_pages, ulong, S_IRUGO);
+MODULE_PARM_DESC(allocated_get_free_pages_bytes, "Memory allocated with get_free_pages");
+
+module_param_named(allocated_vmalloc_bytes, dm_bufio_allocated_vmalloc, ulong, S_IRUGO);
+MODULE_PARM_DESC(allocated_vmalloc_bytes, "Memory allocated with vmalloc");
+
+module_param_named(current_allocated_bytes, dm_bufio_current_allocated, ulong, S_IRUGO);
+MODULE_PARM_DESC(current_allocated_bytes, "Memory currently used by the cache");
+
+MODULE_AUTHOR("Mikulas Patocka <dm-devel@redhat.com>");
+MODULE_DESCRIPTION(DM_NAME " buffered I/O library");
+MODULE_LICENSE("GPL");