[PATCH v2 10/16] btrfs: handle deletions from remapped block group

[Mark Harmstone <mark@harmstone.com>]

Handle the case where we free an extent from a block group that has the
REMAPPED flag set. Because the remap tree is orthogonal to the extent
tree, for data this may be within any number of identity remaps or
actual remaps. If we're freeing a metadata node, this will be wholly
inside one or the other.

btrfs_remove_extent_from_remap_tree() searches the remap tree for the
remaps that cover the range in question, then calls
remove_range_from_remap_tree() for each one, to punch a hole in the
remap and adjust the free-space tree.

For an identity remap, remove_range_from_remap_tree() will adjust the
block group's `identity_remap_count` if this changes. If it reaches
zero we call last_identity_remap_gone(), which removes the chunk's
stripes and device extents - it is now fully remapped.

The changes which involve the block group's ro flag are because the
REMAPPED flag itself prevents a block group from having any new
allocations within it, and so we don't need to account for this
separately.

Signed-off-by: Mark Harmstone <mark@harmstone.com>
---
 fs/btrfs/block-group.c |  82 ++++---
 fs/btrfs/block-group.h |   1 +
 fs/btrfs/disk-io.c     |   1 +
 fs/btrfs/extent-tree.c |  28 ++-
 fs/btrfs/fs.h          |   1 +
 fs/btrfs/relocation.c  | 510 +++++++++++++++++++++++++++++++++++++++++
 fs/btrfs/relocation.h  |   3 +
 fs/btrfs/volumes.c     |  56 +++--
 fs/btrfs/volumes.h     |   6 +
 9 files changed, 630 insertions(+), 58 deletions(-)

diff --git a/fs/btrfs/block-group.c b/fs/btrfs/block-group.c
index 8c28f829547e..7a0524138235 100644
--- a/fs/btrfs/block-group.c
+++ b/fs/btrfs/block-group.c
@@ -1068,6 +1068,32 @@ static int remove_block_group_item(struct btrfs_trans_handle *trans,
 	return ret;
 }
 
+void btrfs_remove_bg_from_sinfo(struct btrfs_block_group *block_group)
+{
+	int factor = btrfs_bg_type_to_factor(block_group->flags);
+
+	spin_lock(&block_group->space_info->lock);
+
+	if (btrfs_test_opt(block_group->fs_info, ENOSPC_DEBUG)) {
+		WARN_ON(block_group->space_info->total_bytes
+			< block_group->length);
+		WARN_ON(block_group->space_info->bytes_readonly
+			< block_group->length - block_group->zone_unusable);
+		WARN_ON(block_group->space_info->bytes_zone_unusable
+			< block_group->zone_unusable);
+		WARN_ON(block_group->space_info->disk_total
+			< block_group->length * factor);
+	}
+	block_group->space_info->total_bytes -= block_group->length;
+	block_group->space_info->bytes_readonly -=
+		(block_group->length - block_group->zone_unusable);
+	btrfs_space_info_update_bytes_zone_unusable(block_group->space_info,
+						    -block_group->zone_unusable);
+	block_group->space_info->disk_total -= block_group->length * factor;
+
+	spin_unlock(&block_group->space_info->lock);
+}
+
 int btrfs_remove_block_group(struct btrfs_trans_handle *trans,
 			     struct btrfs_chunk_map *map)
 {
@@ -1079,7 +1105,6 @@ int btrfs_remove_block_group(struct btrfs_trans_handle *trans,
 	struct kobject *kobj = NULL;
 	int ret;
 	int index;
-	int factor;
 	struct btrfs_caching_control *caching_ctl = NULL;
 	bool remove_map;
 	bool remove_rsv = false;
@@ -1088,7 +1113,7 @@ int btrfs_remove_block_group(struct btrfs_trans_handle *trans,
 	if (!block_group)
 		return -ENOENT;
 
-	BUG_ON(!block_group->ro);
+	BUG_ON(!block_group->ro && !(block_group->flags & BTRFS_BLOCK_GROUP_REMAPPED));
 
 	trace_btrfs_remove_block_group(block_group);
 	/*
@@ -1100,7 +1125,6 @@ int btrfs_remove_block_group(struct btrfs_trans_handle *trans,
 				  block_group->length);
 
 	index = btrfs_bg_flags_to_raid_index(block_group->flags);
-	factor = btrfs_bg_type_to_factor(block_group->flags);
 
 	/* make sure this block group isn't part of an allocation cluster */
 	cluster = &fs_info->data_alloc_cluster;
@@ -1224,26 +1248,11 @@ int btrfs_remove_block_group(struct btrfs_trans_handle *trans,
 
 	spin_lock(&block_group->space_info->lock);
 	list_del_init(&block_group->ro_list);
-
-	if (btrfs_test_opt(fs_info, ENOSPC_DEBUG)) {
-		WARN_ON(block_group->space_info->total_bytes
-			< block_group->length);
-		WARN_ON(block_group->space_info->bytes_readonly
-			< block_group->length - block_group->zone_unusable);
-		WARN_ON(block_group->space_info->bytes_zone_unusable
-			< block_group->zone_unusable);
-		WARN_ON(block_group->space_info->disk_total
-			< block_group->length * factor);
-	}
-	block_group->space_info->total_bytes -= block_group->length;
-	block_group->space_info->bytes_readonly -=
-		(block_group->length - block_group->zone_unusable);
-	btrfs_space_info_update_bytes_zone_unusable(block_group->space_info,
-						    -block_group->zone_unusable);
-	block_group->space_info->disk_total -= block_group->length * factor;
-
 	spin_unlock(&block_group->space_info->lock);
 
+	if (!(block_group->flags & BTRFS_BLOCK_GROUP_REMAPPED))
+		btrfs_remove_bg_from_sinfo(block_group);
+
 	/*
 	 * Remove the free space for the block group from the free space tree
 	 * and the block group's item from the extent tree before marking the
@@ -1539,6 +1548,7 @@ void btrfs_delete_unused_bgs(struct btrfs_fs_info *fs_info)
 	while (!list_empty(&fs_info->unused_bgs)) {
 		u64 used;
 		int trimming;
+		bool made_ro = false;
 
 		block_group = list_first_entry(&fs_info->unused_bgs,
 					       struct btrfs_block_group,
@@ -1575,7 +1585,8 @@ void btrfs_delete_unused_bgs(struct btrfs_fs_info *fs_info)
 
 		spin_lock(&space_info->lock);
 		spin_lock(&block_group->lock);
-		if (btrfs_is_block_group_used(block_group) || block_group->ro ||
+		if (btrfs_is_block_group_used(block_group) ||
+		    (block_group->ro && !(block_group->flags & BTRFS_BLOCK_GROUP_REMAPPED)) ||
 		    list_is_singular(&block_group->list)) {
 			/*
 			 * We want to bail if we made new allocations or have
@@ -1617,9 +1628,10 @@ void btrfs_delete_unused_bgs(struct btrfs_fs_info *fs_info)
 		 * needing to allocate extents from the block group.
 		 */
 		used = btrfs_space_info_used(space_info, true);
-		if ((space_info->total_bytes - block_group->length < used &&
+		if (((space_info->total_bytes - block_group->length < used &&
 		     block_group->zone_unusable < block_group->length) ||
-		    has_unwritten_metadata(block_group)) {
+		    has_unwritten_metadata(block_group)) &&
+			!(block_group->flags & BTRFS_BLOCK_GROUP_REMAPPED)) {
 			spin_unlock(&block_group->lock);
 
 			/*
@@ -1638,8 +1650,14 @@ void btrfs_delete_unused_bgs(struct btrfs_fs_info *fs_info)
 		spin_unlock(&block_group->lock);
 		spin_unlock(&space_info->lock);
 
-		/* We don't want to force the issue, only flip if it's ok. */
-		ret = inc_block_group_ro(block_group, 0);
+		if (!(block_group->flags & BTRFS_BLOCK_GROUP_REMAPPED)) {
+			/* We don't want to force the issue, only flip if it's ok. */
+			ret = inc_block_group_ro(block_group, 0);
+			made_ro = true;
+		} else {
+			ret = 0;
+		}
+
 		up_write(&space_info->groups_sem);
 		if (ret < 0) {
 			ret = 0;
@@ -1648,7 +1666,8 @@ void btrfs_delete_unused_bgs(struct btrfs_fs_info *fs_info)
 
 		ret = btrfs_zone_finish(block_group);
 		if (ret < 0) {
-			btrfs_dec_block_group_ro(block_group);
+			if (made_ro)
+				btrfs_dec_block_group_ro(block_group);
 			if (ret == -EAGAIN) {
 				btrfs_link_bg_list(block_group, &retry_list);
 				ret = 0;
@@ -1663,7 +1682,8 @@ void btrfs_delete_unused_bgs(struct btrfs_fs_info *fs_info)
 		trans = btrfs_start_trans_remove_block_group(fs_info,
 						     block_group->start);
 		if (IS_ERR(trans)) {
-			btrfs_dec_block_group_ro(block_group);
+			if (made_ro)
+				btrfs_dec_block_group_ro(block_group);
 			ret = PTR_ERR(trans);
 			goto next;
 		}
@@ -1673,7 +1693,8 @@ void btrfs_delete_unused_bgs(struct btrfs_fs_info *fs_info)
 		 * just delete them, we don't care about them anymore.
 		 */
 		if (!clean_pinned_extents(trans, block_group)) {
-			btrfs_dec_block_group_ro(block_group);
+			if (made_ro)
+				btrfs_dec_block_group_ro(block_group);
 			goto end_trans;
 		}
 
@@ -1687,7 +1708,8 @@ void btrfs_delete_unused_bgs(struct btrfs_fs_info *fs_info)
 		spin_lock(&fs_info->discard_ctl.lock);
 		if (!list_empty(&block_group->discard_list)) {
 			spin_unlock(&fs_info->discard_ctl.lock);
-			btrfs_dec_block_group_ro(block_group);
+			if (made_ro)
+				btrfs_dec_block_group_ro(block_group);
 			btrfs_discard_queue_work(&fs_info->discard_ctl,
 						 block_group);
 			goto end_trans;
diff --git a/fs/btrfs/block-group.h b/fs/btrfs/block-group.h
index ecc89701b2ea..0433b0127ed8 100644
--- a/fs/btrfs/block-group.h
+++ b/fs/btrfs/block-group.h
@@ -336,6 +336,7 @@ int btrfs_add_new_free_space(struct btrfs_block_group *block_group,
 struct btrfs_trans_handle *btrfs_start_trans_remove_block_group(
 				struct btrfs_fs_info *fs_info,
 				const u64 chunk_offset);
+void btrfs_remove_bg_from_sinfo(struct btrfs_block_group *block_group);
 int btrfs_remove_block_group(struct btrfs_trans_handle *trans,
 			     struct btrfs_chunk_map *map);
 void btrfs_delete_unused_bgs(struct btrfs_fs_info *fs_info);
diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
index 563aea5e3b1b..d92d08316322 100644
--- a/fs/btrfs/disk-io.c
+++ b/fs/btrfs/disk-io.c
@@ -2907,6 +2907,7 @@ void btrfs_init_fs_info(struct btrfs_fs_info *fs_info)
 	mutex_init(&fs_info->chunk_mutex);
 	mutex_init(&fs_info->transaction_kthread_mutex);
 	mutex_init(&fs_info->cleaner_mutex);
+	mutex_init(&fs_info->remap_mutex);
 	mutex_init(&fs_info->ro_block_group_mutex);
 	init_rwsem(&fs_info->commit_root_sem);
 	init_rwsem(&fs_info->cleanup_work_sem);
diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
index c1b96c728fe6..ca3f6d6bb5ba 100644
--- a/fs/btrfs/extent-tree.c
+++ b/fs/btrfs/extent-tree.c
@@ -40,6 +40,7 @@
 #include "orphan.h"
 #include "tree-checker.h"
 #include "raid-stripe-tree.h"
+#include "relocation.h"
 
 #undef SCRAMBLE_DELAYED_REFS
 
@@ -2999,7 +3000,8 @@ u64 btrfs_get_extent_owner_root(struct btrfs_fs_info *fs_info,
 }
 
 static int do_free_extent_accounting(struct btrfs_trans_handle *trans,
-				     u64 bytenr, struct btrfs_squota_delta *delta)
+				     u64 bytenr, struct btrfs_squota_delta *delta,
+				     bool remapped)
 {
 	int ret;
 	u64 num_bytes = delta->num_bytes;
@@ -3027,10 +3029,16 @@ static int do_free_extent_accounting(struct btrfs_trans_handle *trans,
 		return ret;
 	}
 
-	ret = btrfs_add_to_free_space_tree(trans, bytenr, num_bytes);
-	if (ret) {
-		btrfs_abort_transaction(trans, ret);
-		return ret;
+	/*
+	 * If remapped, FST has already been taken care of in
+	 * remove_range_from_remap_tree().
+	 */
+	if (!remapped) {
+		ret = btrfs_add_to_free_space_tree(trans, bytenr, num_bytes);
+		if (ret) {
+			btrfs_abort_transaction(trans, ret);
+			return ret;
+		}
 	}
 
 	ret = btrfs_update_block_group(trans, bytenr, num_bytes, false);
@@ -3396,7 +3404,15 @@ static int __btrfs_free_extent(struct btrfs_trans_handle *trans,
 		}
 		btrfs_release_path(path);
 
-		ret = do_free_extent_accounting(trans, bytenr, &delta);
+		/* returns 1 on success and 0 on no-op */
+		ret = btrfs_remove_extent_from_remap_tree(trans, path, bytenr,
+							  num_bytes);
+		if (ret < 0) {
+			btrfs_abort_transaction(trans, ret);
+			goto out;
+		}
+
+		ret = do_free_extent_accounting(trans, bytenr, &delta, ret);
 	}
 	btrfs_release_path(path);
 
diff --git a/fs/btrfs/fs.h b/fs/btrfs/fs.h
index 6ea96e76655e..dbb7de95241b 100644
--- a/fs/btrfs/fs.h
+++ b/fs/btrfs/fs.h
@@ -547,6 +547,7 @@ struct btrfs_fs_info {
 	struct mutex transaction_kthread_mutex;
 	struct mutex cleaner_mutex;
 	struct mutex chunk_mutex;
+	struct mutex remap_mutex;
 
 	/*
 	 * This is taken to make sure we don't set block groups ro after the
diff --git a/fs/btrfs/relocation.c b/fs/btrfs/relocation.c
index e1f1da9336e7..03a1246af678 100644
--- a/fs/btrfs/relocation.c
+++ b/fs/btrfs/relocation.c
@@ -37,6 +37,7 @@
 #include "super.h"
 #include "tree-checker.h"
 #include "raid-stripe-tree.h"
+#include "free-space-tree.h"
 
 /*
  * Relocation overview
@@ -3884,6 +3885,148 @@ static const char *stage_to_string(enum reloc_stage stage)
 	return "unknown";
 }
 
+static void adjust_block_group_remap_bytes(struct btrfs_trans_handle *trans,
+					   struct btrfs_block_group *bg,
+					   s64 diff)
+{
+	struct btrfs_fs_info *fs_info = trans->fs_info;
+	bool bg_already_dirty = true;
+
+	bg->remap_bytes += diff;
+
+	if (bg->used == 0 && bg->remap_bytes == 0)
+		btrfs_mark_bg_unused(bg);
+
+	spin_lock(&trans->transaction->dirty_bgs_lock);
+	if (list_empty(&bg->dirty_list)) {
+		list_add_tail(&bg->dirty_list, &trans->transaction->dirty_bgs);
+		bg_already_dirty = false;
+		btrfs_get_block_group(bg);
+	}
+	spin_unlock(&trans->transaction->dirty_bgs_lock);
+
+	/* Modified block groups are accounted for in the delayed_refs_rsv. */
+	if (!bg_already_dirty)
+		btrfs_inc_delayed_refs_rsv_bg_updates(fs_info);
+}
+
+static int remove_chunk_stripes(struct btrfs_trans_handle *trans,
+				struct btrfs_chunk_map *chunk,
+				struct btrfs_path *path)
+{
+	struct btrfs_fs_info *fs_info = trans->fs_info;
+	struct btrfs_key key;
+	struct extent_buffer *leaf;
+	struct btrfs_chunk *c;
+	int ret;
+
+	key.objectid = BTRFS_FIRST_CHUNK_TREE_OBJECTID;
+	key.type = BTRFS_CHUNK_ITEM_KEY;
+	key.offset = chunk->start;
+
+	ret = btrfs_search_slot(trans, fs_info->chunk_root, &key, path,
+				0, 1);
+	if (ret) {
+		if (ret == 1) {
+			btrfs_release_path(path);
+			ret = -ENOENT;
+		}
+		return ret;
+	}
+
+	leaf = path->nodes[0];
+
+	c = btrfs_item_ptr(leaf, path->slots[0], struct btrfs_chunk);
+	btrfs_set_chunk_num_stripes(leaf, c, 0);
+
+	btrfs_truncate_item(trans, path, offsetof(struct btrfs_chunk, stripe),
+			    1);
+
+	btrfs_mark_buffer_dirty(trans, leaf);
+
+	btrfs_release_path(path);
+
+	return 0;
+}
+
+static int last_identity_remap_gone(struct btrfs_trans_handle *trans,
+				    struct btrfs_chunk_map *chunk,
+				    struct btrfs_block_group *bg,
+				    struct btrfs_path *path)
+{
+	int ret;
+
+	ret = btrfs_remove_dev_extents(trans, chunk);
+	if (ret)
+		return ret;
+
+	mutex_lock(&trans->fs_info->chunk_mutex);
+
+	for (unsigned int i = 0; i < chunk->num_stripes; i++) {
+		ret = btrfs_update_device(trans, chunk->stripes[i].dev);
+		if (ret) {
+			mutex_unlock(&trans->fs_info->chunk_mutex);
+			return ret;
+		}
+	}
+
+	mutex_unlock(&trans->fs_info->chunk_mutex);
+
+	write_lock(&trans->fs_info->mapping_tree_lock);
+	btrfs_chunk_map_device_clear_bits(chunk, CHUNK_ALLOCATED);
+	write_unlock(&trans->fs_info->mapping_tree_lock);
+
+	btrfs_remove_bg_from_sinfo(bg);
+
+	ret = remove_chunk_stripes(trans, chunk, path);
+	if (ret)
+		return ret;
+
+	return 0;
+}
+
+static int adjust_identity_remap_count(struct btrfs_trans_handle *trans,
+				       struct btrfs_path *path,
+				       struct btrfs_block_group *bg, int delta)
+{
+	struct btrfs_fs_info *fs_info = trans->fs_info;
+	struct btrfs_chunk_map *chunk;
+	bool bg_already_dirty = true;
+	int ret;
+
+	WARN_ON(delta < 0 && -delta > bg->identity_remap_count);
+
+	bg->identity_remap_count += delta;
+
+	spin_lock(&trans->transaction->dirty_bgs_lock);
+	if (list_empty(&bg->dirty_list)) {
+		list_add_tail(&bg->dirty_list, &trans->transaction->dirty_bgs);
+		bg_already_dirty = false;
+		btrfs_get_block_group(bg);
+	}
+	spin_unlock(&trans->transaction->dirty_bgs_lock);
+
+	/* Modified block groups are accounted for in the delayed_refs_rsv. */
+	if (!bg_already_dirty)
+		btrfs_inc_delayed_refs_rsv_bg_updates(fs_info);
+
+	if (bg->identity_remap_count != 0)
+		return 0;
+
+	chunk = btrfs_find_chunk_map(fs_info, bg->start, 1);
+	if (!chunk)
+		return -ENOENT;
+
+	ret = last_identity_remap_gone(trans, chunk, bg, path);
+	if (ret)
+		goto end;
+
+	ret = 0;
+end:
+	btrfs_free_chunk_map(chunk);
+	return ret;
+}
+
 int btrfs_translate_remap(struct btrfs_fs_info *fs_info, u64 *logical,
 			  u64 *length, bool nolock)
 {
@@ -4504,3 +4647,370 @@ u64 btrfs_get_reloc_bg_bytenr(const struct btrfs_fs_info *fs_info)
 		logical = fs_info->reloc_ctl->block_group->start;
 	return logical;
 }
+
+static int remove_range_from_remap_tree(struct btrfs_trans_handle *trans,
+					struct btrfs_path *path,
+					struct btrfs_block_group *bg,
+					u64 bytenr, u64 num_bytes)
+{
+	int ret;
+	struct btrfs_fs_info *fs_info = trans->fs_info;
+	struct extent_buffer *leaf = path->nodes[0];
+	struct btrfs_key key, new_key;
+	struct btrfs_remap *remap_ptr = NULL, remap;
+	struct btrfs_block_group *dest_bg = NULL;
+	u64 end, new_addr = 0, remap_start, remap_length, overlap_length;
+	bool is_identity_remap;
+
+	end = bytenr + num_bytes;
+
+	btrfs_item_key_to_cpu(leaf, &key, path->slots[0]);
+
+	is_identity_remap = key.type == BTRFS_IDENTITY_REMAP_KEY;
+
+	remap_start = key.objectid;
+	remap_length = key.offset;
+
+	if (!is_identity_remap) {
+		remap_ptr = btrfs_item_ptr(leaf, path->slots[0],
+					   struct btrfs_remap);
+		new_addr = btrfs_remap_address(leaf, remap_ptr);
+
+		dest_bg = btrfs_lookup_block_group(fs_info, new_addr);
+	}
+
+	if (bytenr == remap_start && num_bytes >= remap_length) {
+		/* Remove entirely. */
+
+		ret = btrfs_del_item(trans, fs_info->remap_root, path);
+		if (ret)
+			goto end;
+
+		btrfs_release_path(path);
+
+		overlap_length = remap_length;
+
+		if (!is_identity_remap) {
+			/* Remove backref. */
+
+			key.objectid = new_addr;
+			key.type = BTRFS_REMAP_BACKREF_KEY;
+			key.offset = remap_length;
+
+			ret = btrfs_search_slot(trans, fs_info->remap_root,
+						&key, path, -1, 1);
+			if (ret) {
+				if (ret == 1) {
+					btrfs_release_path(path);
+					ret = -ENOENT;
+				}
+				goto end;
+			}
+
+			ret = btrfs_del_item(trans, fs_info->remap_root, path);
+
+			btrfs_release_path(path);
+
+			if (ret)
+				goto end;
+
+			adjust_block_group_remap_bytes(trans, dest_bg,
+						       -remap_length);
+		} else {
+			ret = adjust_identity_remap_count(trans, path, bg, -1);
+			if (ret)
+				goto end;
+		}
+	} else if (bytenr == remap_start) {
+		/* Remove beginning. */
+
+		new_key.objectid = end;
+		new_key.type = key.type;
+		new_key.offset = remap_length + remap_start - end;
+
+		btrfs_set_item_key_safe(trans, path, &new_key);
+		btrfs_mark_buffer_dirty(trans, leaf);
+
+		overlap_length = num_bytes;
+
+		if (!is_identity_remap) {
+			btrfs_set_remap_address(leaf, remap_ptr,
+						new_addr + end - remap_start);
+			btrfs_release_path(path);
+
+			/* Adjust backref. */
+
+			key.objectid = new_addr;
+			key.type = BTRFS_REMAP_BACKREF_KEY;
+			key.offset = remap_length;
+
+			ret = btrfs_search_slot(trans, fs_info->remap_root,
+						&key, path, -1, 1);
+			if (ret) {
+				if (ret == 1) {
+					btrfs_release_path(path);
+					ret = -ENOENT;
+				}
+				goto end;
+			}
+
+			leaf = path->nodes[0];
+
+			new_key.objectid = new_addr + end - remap_start;
+			new_key.type = BTRFS_REMAP_BACKREF_KEY;
+			new_key.offset = remap_length + remap_start - end;
+
+			btrfs_set_item_key_safe(trans, path, &new_key);
+
+			remap_ptr = btrfs_item_ptr(leaf, path->slots[0],
+						   struct btrfs_remap);
+			btrfs_set_remap_address(leaf, remap_ptr, end);
+
+			btrfs_mark_buffer_dirty(trans, path->nodes[0]);
+
+			btrfs_release_path(path);
+
+			adjust_block_group_remap_bytes(trans, dest_bg,
+						       -num_bytes);
+		}
+	} else if (bytenr + num_bytes < remap_start + remap_length) {
+		/* Remove middle. */
+
+		new_key.objectid = remap_start;
+		new_key.type = key.type;
+		new_key.offset = bytenr - remap_start;
+
+		btrfs_set_item_key_safe(trans, path, &new_key);
+		btrfs_mark_buffer_dirty(trans, leaf);
+
+		new_key.objectid = end;
+		new_key.offset = remap_start + remap_length - end;
+
+		btrfs_release_path(path);
+
+		overlap_length = num_bytes;
+
+		if (!is_identity_remap) {
+			/* Add second remap entry. */
+
+			ret = btrfs_insert_empty_item(trans, fs_info->remap_root,
+						path, &new_key,
+						sizeof(struct btrfs_remap));
+			if (ret)
+				goto end;
+
+			btrfs_set_stack_remap_address(&remap,
+						new_addr + end - remap_start);
+
+			write_extent_buffer(path->nodes[0], &remap,
+				btrfs_item_ptr_offset(path->nodes[0], path->slots[0]),
+				sizeof(struct btrfs_remap));
+
+			btrfs_release_path(path);
+
+			/* Shorten backref entry. */
+
+			key.objectid = new_addr;
+			key.type = BTRFS_REMAP_BACKREF_KEY;
+			key.offset = remap_length;
+
+			ret = btrfs_search_slot(trans, fs_info->remap_root,
+						&key, path, -1, 1);
+			if (ret) {
+				if (ret == 1) {
+					btrfs_release_path(path);
+					ret = -ENOENT;
+				}
+				goto end;
+			}
+
+			new_key.objectid = new_addr;
+			new_key.type = BTRFS_REMAP_BACKREF_KEY;
+			new_key.offset = bytenr - remap_start;
+
+			btrfs_set_item_key_safe(trans, path, &new_key);
+			btrfs_mark_buffer_dirty(trans, path->nodes[0]);
+
+			btrfs_release_path(path);
+
+			/* Add second backref entry. */
+
+			new_key.objectid = new_addr + end - remap_start;
+			new_key.type = BTRFS_REMAP_BACKREF_KEY;
+			new_key.offset = remap_start + remap_length - end;
+
+			ret = btrfs_insert_empty_item(trans, fs_info->remap_root,
+						path, &new_key,
+						sizeof(struct btrfs_remap));
+			if (ret)
+				goto end;
+
+			btrfs_set_stack_remap_address(&remap, end);
+
+			write_extent_buffer(path->nodes[0], &remap,
+				btrfs_item_ptr_offset(path->nodes[0], path->slots[0]),
+				sizeof(struct btrfs_remap));
+
+			btrfs_release_path(path);
+
+			adjust_block_group_remap_bytes(trans, dest_bg,
+						       -num_bytes);
+		} else {
+			/* Add second identity remap entry. */
+
+			ret = btrfs_insert_empty_item(trans, fs_info->remap_root,
+						      path, &new_key, 0);
+			if (ret)
+				goto end;
+
+			btrfs_release_path(path);
+
+			ret = adjust_identity_remap_count(trans, path, bg, 1);
+			if (ret)
+				goto end;
+		}
+	} else {
+		/* Remove end. */
+
+		new_key.objectid = remap_start;
+		new_key.type = key.type;
+		new_key.offset = bytenr - remap_start;
+
+		btrfs_set_item_key_safe(trans, path, &new_key);
+		btrfs_mark_buffer_dirty(trans, leaf);
+
+		btrfs_release_path(path);
+
+		overlap_length = remap_start + remap_length - bytenr;
+
+		if (!is_identity_remap) {
+			/* Shorten backref entry. */
+
+			key.objectid = new_addr;
+			key.type = BTRFS_REMAP_BACKREF_KEY;
+			key.offset = remap_length;
+
+			ret = btrfs_search_slot(trans, fs_info->remap_root,
+						&key, path, -1, 1);
+			if (ret) {
+				if (ret == 1) {
+					btrfs_release_path(path);
+					ret = -ENOENT;
+				}
+				goto end;
+			}
+
+			new_key.objectid = new_addr;
+			new_key.type = BTRFS_REMAP_BACKREF_KEY;
+			new_key.offset = bytenr - remap_start;
+
+			btrfs_set_item_key_safe(trans, path, &new_key);
+			btrfs_mark_buffer_dirty(trans, path->nodes[0]);
+
+			btrfs_release_path(path);
+
+			adjust_block_group_remap_bytes(trans, dest_bg,
+					bytenr - remap_start - remap_length);
+		}
+	}
+
+	if (!is_identity_remap) {
+		ret = btrfs_add_to_free_space_tree(trans,
+					     bytenr - remap_start + new_addr,
+					     overlap_length);
+		if (ret)
+			goto end;
+	}
+
+	ret = overlap_length;
+
+end:
+	if (dest_bg)
+		btrfs_put_block_group(dest_bg);
+
+	return ret;
+}
+
+/*
+ * Returns 1 if remove_range_from_remap_tree() has been called successfully,
+ * 0 if block group wasn't remapped, and a negative number on error.
+ */
+int btrfs_remove_extent_from_remap_tree(struct btrfs_trans_handle *trans,
+					struct btrfs_path *path,
+					u64 bytenr, u64 num_bytes)
+{
+	struct btrfs_fs_info *fs_info = trans->fs_info;
+	struct btrfs_key key, found_key;
+	struct extent_buffer *leaf;
+	struct btrfs_block_group *bg;
+	int ret, length;
+
+	if (!(btrfs_super_incompat_flags(fs_info->super_copy) &
+	      BTRFS_FEATURE_INCOMPAT_REMAP_TREE))
+		return 0;
+
+	bg = btrfs_lookup_block_group(fs_info, bytenr);
+	if (!bg)
+		return 0;
+
+	mutex_lock(&fs_info->remap_mutex);
+
+	if (!(bg->flags & BTRFS_BLOCK_GROUP_REMAPPED)) {
+		mutex_unlock(&fs_info->remap_mutex);
+		btrfs_put_block_group(bg);
+		return 0;
+	}
+
+	do {
+		key.objectid = bytenr;
+		key.type = (u8)-1;
+		key.offset = (u64)-1;
+
+		ret = btrfs_search_slot(trans, fs_info->remap_root, &key, path,
+					-1, 1);
+		if (ret < 0)
+			goto end;
+
+		leaf = path->nodes[0];
+
+		if (path->slots[0] == 0) {
+			ret = -ENOENT;
+			goto end;
+		}
+
+		path->slots[0]--;
+
+		btrfs_item_key_to_cpu(leaf, &found_key, path->slots[0]);
+
+		if (found_key.type != BTRFS_IDENTITY_REMAP_KEY &&
+		    found_key.type != BTRFS_REMAP_KEY) {
+			ret = -ENOENT;
+			goto end;
+		}
+
+		if (bytenr < found_key.objectid ||
+		    bytenr >= found_key.objectid + found_key.offset) {
+			ret = -ENOENT;
+			goto end;
+		}
+
+		length = remove_range_from_remap_tree(trans, path, bg, bytenr,
+						      num_bytes);
+		if (length < 0) {
+			ret = length;
+			goto end;
+		}
+
+		bytenr += length;
+		num_bytes -= length;
+	} while (num_bytes > 0);
+
+	ret = 1;
+
+end:
+	mutex_unlock(&fs_info->remap_mutex);
+
+	btrfs_put_block_group(bg);
+	btrfs_release_path(path);
+	return ret;
+}
diff --git a/fs/btrfs/relocation.h b/fs/btrfs/relocation.h
index a653c42a25a3..4b0bb34b3fc1 100644
--- a/fs/btrfs/relocation.h
+++ b/fs/btrfs/relocation.h
@@ -33,5 +33,8 @@ bool btrfs_should_ignore_reloc_root(const struct btrfs_root *root);
 u64 btrfs_get_reloc_bg_bytenr(const struct btrfs_fs_info *fs_info);
 int btrfs_translate_remap(struct btrfs_fs_info *fs_info, u64 *logical,
 			  u64 *length, bool nolock);
+int btrfs_remove_extent_from_remap_tree(struct btrfs_trans_handle *trans,
+					struct btrfs_path *path,
+					u64 bytenr, u64 num_bytes);
 
 #endif
diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
index a2c49cb8bfc6..fc2b3e7de32e 100644
--- a/fs/btrfs/volumes.c
+++ b/fs/btrfs/volumes.c
@@ -2941,8 +2941,8 @@ int btrfs_init_new_device(struct btrfs_fs_info *fs_info, const char *device_path
 	return ret;
 }
 
-static noinline int btrfs_update_device(struct btrfs_trans_handle *trans,
-					struct btrfs_device *device)
+int btrfs_update_device(struct btrfs_trans_handle *trans,
+			struct btrfs_device *device)
 {
 	int ret;
 	struct btrfs_path *path;
@@ -3246,25 +3246,13 @@ static int remove_chunk_item(struct btrfs_trans_handle *trans,
 	return btrfs_free_chunk(trans, chunk_offset);
 }
 
-int btrfs_remove_chunk(struct btrfs_trans_handle *trans, u64 chunk_offset)
+int btrfs_remove_dev_extents(struct btrfs_trans_handle *trans,
+			     struct btrfs_chunk_map *map)
 {
 	struct btrfs_fs_info *fs_info = trans->fs_info;
-	struct btrfs_chunk_map *map;
+	struct btrfs_fs_devices *fs_devices = fs_info->fs_devices;
 	u64 dev_extent_len = 0;
 	int i, ret = 0;
-	struct btrfs_fs_devices *fs_devices = fs_info->fs_devices;
-
-	map = btrfs_get_chunk_map(fs_info, chunk_offset, 1);
-	if (IS_ERR(map)) {
-		/*
-		 * This is a logic error, but we don't want to just rely on the
-		 * user having built with ASSERT enabled, so if ASSERT doesn't
-		 * do anything we still error out.
-		 */
-		DEBUG_WARN("errr %ld reading chunk map at offset %llu",
-			   PTR_ERR(map), chunk_offset);
-		return PTR_ERR(map);
-	}
 
 	/*
 	 * First delete the device extent items from the devices btree.
@@ -3285,7 +3273,7 @@ int btrfs_remove_chunk(struct btrfs_trans_handle *trans, u64 chunk_offset)
 		if (ret) {
 			mutex_unlock(&fs_devices->device_list_mutex);
 			btrfs_abort_transaction(trans, ret);
-			goto out;
+			return ret;
 		}
 
 		if (device->bytes_used > 0) {
@@ -3305,6 +3293,30 @@ int btrfs_remove_chunk(struct btrfs_trans_handle *trans, u64 chunk_offset)
 	}
 	mutex_unlock(&fs_devices->device_list_mutex);
 
+	return 0;
+}
+
+int btrfs_remove_chunk(struct btrfs_trans_handle *trans, u64 chunk_offset)
+{
+	struct btrfs_fs_info *fs_info = trans->fs_info;
+	struct btrfs_chunk_map *map;
+	int ret;
+
+	map = btrfs_get_chunk_map(fs_info, chunk_offset, 1);
+	if (IS_ERR(map)) {
+		/*
+		 * This is a logic error, but we don't want to just rely on the
+		 * user having built with ASSERT enabled, so if ASSERT doesn't
+		 * do anything we still error out.
+		 */
+		ASSERT(0);
+		return PTR_ERR(map);
+	}
+
+	ret = btrfs_remove_dev_extents(trans, map);
+	if (ret)
+		goto out;
+
 	/*
 	 * We acquire fs_info->chunk_mutex for 2 reasons:
 	 *
@@ -5448,7 +5460,7 @@ static void chunk_map_device_set_bits(struct btrfs_chunk_map *map, unsigned int
 	}
 }
 
-static void chunk_map_device_clear_bits(struct btrfs_chunk_map *map, unsigned int bits)
+void btrfs_chunk_map_device_clear_bits(struct btrfs_chunk_map *map, unsigned int bits)
 {
 	for (int i = 0; i < map->num_stripes; i++) {
 		struct btrfs_io_stripe *stripe = &map->stripes[i];
@@ -5465,7 +5477,7 @@ void btrfs_remove_chunk_map(struct btrfs_fs_info *fs_info, struct btrfs_chunk_ma
 	write_lock(&fs_info->mapping_tree_lock);
 	rb_erase_cached(&map->rb_node, &fs_info->mapping_tree);
 	RB_CLEAR_NODE(&map->rb_node);
-	chunk_map_device_clear_bits(map, CHUNK_ALLOCATED);
+	btrfs_chunk_map_device_clear_bits(map, CHUNK_ALLOCATED);
 	write_unlock(&fs_info->mapping_tree_lock);
 
 	/* Once for the tree reference. */
@@ -5501,7 +5513,7 @@ int btrfs_add_chunk_map(struct btrfs_fs_info *fs_info, struct btrfs_chunk_map *m
 		return -EEXIST;
 	}
 	chunk_map_device_set_bits(map, CHUNK_ALLOCATED);
-	chunk_map_device_clear_bits(map, CHUNK_TRIMMED);
+	btrfs_chunk_map_device_clear_bits(map, CHUNK_TRIMMED);
 	write_unlock(&fs_info->mapping_tree_lock);
 
 	return 0;
@@ -5866,7 +5878,7 @@ void btrfs_mapping_tree_free(struct btrfs_fs_info *fs_info)
 		map = rb_entry(node, struct btrfs_chunk_map, rb_node);
 		rb_erase_cached(&map->rb_node, &fs_info->mapping_tree);
 		RB_CLEAR_NODE(&map->rb_node);
-		chunk_map_device_clear_bits(map, CHUNK_ALLOCATED);
+		btrfs_chunk_map_device_clear_bits(map, CHUNK_ALLOCATED);
 		/* Once for the tree ref. */
 		btrfs_free_chunk_map(map);
 		cond_resched_rwlock_write(&fs_info->mapping_tree_lock);
diff --git a/fs/btrfs/volumes.h b/fs/btrfs/volumes.h
index 430be12fd5e7..64b34710b68b 100644
--- a/fs/btrfs/volumes.h
+++ b/fs/btrfs/volumes.h
@@ -789,6 +789,8 @@ u64 btrfs_calc_stripe_length(const struct btrfs_chunk_map *map);
 int btrfs_nr_parity_stripes(u64 type);
 int btrfs_chunk_alloc_add_chunk_item(struct btrfs_trans_handle *trans,
 				     struct btrfs_block_group *bg);
+int btrfs_remove_dev_extents(struct btrfs_trans_handle *trans,
+			     struct btrfs_chunk_map *map);
 int btrfs_remove_chunk(struct btrfs_trans_handle *trans, u64 chunk_offset);
 
 #ifdef CONFIG_BTRFS_FS_RUN_SANITY_TESTS
@@ -900,6 +902,10 @@ bool btrfs_repair_one_zone(struct btrfs_fs_info *fs_info, u64 logical);
 
 bool btrfs_pinned_by_swapfile(struct btrfs_fs_info *fs_info, void *ptr);
 const u8 *btrfs_sb_fsid_ptr(const struct btrfs_super_block *sb);
+int btrfs_update_device(struct btrfs_trans_handle *trans,
+			struct btrfs_device *device);
+void btrfs_chunk_map_device_clear_bits(struct btrfs_chunk_map *map,
+				       unsigned int bits);
 
 #ifdef CONFIG_BTRFS_FS_RUN_SANITY_TESTS
 struct btrfs_io_context *alloc_btrfs_io_context(struct btrfs_fs_info *fs_info,
-- 
2.49.1