[PATCH v7 12/16] btrfs: replace identity remaps with actual remaps when doing relocations

[Mark Harmstone <mark@harmstone.com>]

Add a function do_remap_tree_reloc(), which does the actual work of
doing a relocation using the remap tree.

In a loop we call do_remap_reloc_trans(), which searches for the first
identity remap for the block group. We call btrfs_reserve_extent() to
find space elsewhere for it, and read the data into memory and write it
to the new location. We then carve out the identity remap and replace it
with an actual remap, which points to the new location in which to look.

Once the last identity remap has been removed we call
last_identity_remap_gone(), which, as with deletions, removes the
chunk's stripes and device extents.

Signed-off-by: Mark Harmstone <mark@harmstone.com>
Reviewed-by: Boris Burkov <boris@bur.io>
---
 fs/btrfs/relocation.c | 336 ++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 336 insertions(+)

diff --git a/fs/btrfs/relocation.c b/fs/btrfs/relocation.c
index 3c486894b6b4..2e1a87ab0509 100644
--- a/fs/btrfs/relocation.c
+++ b/fs/btrfs/relocation.c
@@ -4640,6 +4640,61 @@ static int create_remap_tree_entries(struct btrfs_trans_handle *trans,
 	return ret;
 }
 
+static int find_next_identity_remap(struct btrfs_trans_handle *trans,
+				    struct btrfs_path *path, u64 bg_end,
+				    u64 last_start, u64 *start,
+				    u64 *length)
+{
+	int ret;
+	struct btrfs_key key, found_key;
+	struct btrfs_root *remap_root = trans->fs_info->remap_root;
+	struct extent_buffer *leaf;
+
+	key.objectid = last_start;
+	key.type = BTRFS_IDENTITY_REMAP_KEY;
+	key.offset = 0;
+
+	ret = btrfs_search_slot(trans, remap_root, &key, path, 0, 0);
+	if (ret < 0)
+		goto out;
+
+	leaf = path->nodes[0];
+	while (true) {
+		if (path->slots[0] >= btrfs_header_nritems(leaf)) {
+			ret = btrfs_next_leaf(remap_root, path);
+
+			if (ret != 0) {
+				if (ret == 1)
+					ret = -ENOENT;
+				goto out;
+			}
+
+			leaf = path->nodes[0];
+		}
+
+		btrfs_item_key_to_cpu(leaf, &found_key, path->slots[0]);
+
+		if (found_key.objectid >= bg_end) {
+			ret = -ENOENT;
+			goto out;
+		}
+
+		if (found_key.type == BTRFS_IDENTITY_REMAP_KEY) {
+			*start = found_key.objectid;
+			*length = found_key.offset;
+			ret = 0;
+			goto out;
+		}
+
+		path->slots[0]++;
+	}
+
+out:
+	btrfs_release_path(path);
+
+	return ret;
+}
+
 static int remove_chunk_stripes(struct btrfs_trans_handle *trans,
 				struct btrfs_chunk_map *chunk,
 				struct btrfs_path *path)
@@ -4785,6 +4840,96 @@ static void adjust_identity_remap_count(struct btrfs_trans_handle *trans,
 		btrfs_mark_bg_fully_remapped(bg, trans);
 }
 
+static int add_remap_entry(struct btrfs_trans_handle *trans,
+			   struct btrfs_path *path,
+			   struct btrfs_block_group *src_bg, u64 old_addr,
+			   u64 new_addr, u64 length)
+{
+	struct btrfs_fs_info *fs_info = trans->fs_info;
+	struct btrfs_key key, new_key;
+	int ret;
+	int identity_count_delta = 0;
+
+	key.objectid = old_addr;
+	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;
+
+	if (path->slots[0] == 0) {
+		ret = -ENOENT;
+		goto end;
+	}
+
+	path->slots[0]--;
+
+	btrfs_item_key_to_cpu(path->nodes[0], &key, path->slots[0]);
+
+	if (key.type != BTRFS_IDENTITY_REMAP_KEY ||
+	    key.objectid > old_addr ||
+	    key.objectid + key.offset <= old_addr) {
+		ret = -ENOENT;
+		goto end;
+	}
+
+	/* Shorten or delete identity mapping entry. */
+
+	if (key.objectid == old_addr) {
+		ret = btrfs_del_item(trans, fs_info->remap_root, path);
+		if (ret)
+			goto end;
+
+		identity_count_delta--;
+	} else {
+		new_key.objectid = key.objectid;
+		new_key.type = BTRFS_IDENTITY_REMAP_KEY;
+		new_key.offset = old_addr - key.objectid;
+
+		btrfs_set_item_key_safe(trans, path, &new_key);
+	}
+
+	btrfs_release_path(path);
+
+	/* Create new remap entry. */
+
+	ret = add_remap_item(trans, path, new_addr, length, old_addr);
+	if (ret)
+		goto end;
+
+	/* Add entry for remainder of identity mapping, if necessary. */
+
+	if (key.objectid + key.offset != old_addr + length) {
+		new_key.objectid = old_addr + length;
+		new_key.type = BTRFS_IDENTITY_REMAP_KEY;
+		new_key.offset = key.objectid + key.offset - old_addr - length;
+
+		ret = btrfs_insert_empty_item(trans, fs_info->remap_root,
+					      path, &new_key, 0);
+		if (ret)
+			goto end;
+
+		btrfs_release_path(path);
+
+		identity_count_delta++;
+	}
+
+	/* Add backref. */
+
+	ret = add_remap_backref_item(trans, path, new_addr, length, old_addr);
+	if (ret)
+		goto end;
+
+	if (identity_count_delta != 0)
+		adjust_identity_remap_count(trans, src_bg, identity_count_delta);
+
+end:
+	btrfs_release_path(path);
+
+	return ret;
+}
+
 static int mark_chunk_remapped(struct btrfs_trans_handle *trans,
 			       struct btrfs_path *path, uint64_t start)
 {
@@ -4834,6 +4979,189 @@ static int mark_chunk_remapped(struct btrfs_trans_handle *trans,
 	return ret;
 }
 
+static int do_remap_reloc_trans(struct btrfs_fs_info *fs_info,
+				struct btrfs_block_group *src_bg,
+				struct btrfs_path *path, u64 *last_start)
+{
+	struct btrfs_trans_handle *trans;
+	struct btrfs_root *extent_root;
+	struct btrfs_key ins;
+	struct btrfs_block_group *dest_bg = NULL;
+	u64 start, remap_length, length, new_addr, min_size;
+	int ret;
+	bool no_more = false;
+	bool is_data = src_bg->flags & BTRFS_BLOCK_GROUP_DATA;
+	bool made_reservation = false, bg_needs_free_space;
+	struct btrfs_space_info *sinfo = src_bg->space_info;
+
+	extent_root = btrfs_extent_root(fs_info, src_bg->start);
+
+	trans = btrfs_start_transaction(extent_root, 0);
+	if (IS_ERR(trans))
+		return PTR_ERR(trans);
+
+	mutex_lock(&fs_info->remap_mutex);
+
+	ret = find_next_identity_remap(trans, path, src_bg->start + src_bg->length,
+				       *last_start, &start, &remap_length);
+	if (ret == -ENOENT) {
+		no_more = true;
+		goto next;
+	} else if (ret) {
+		mutex_unlock(&fs_info->remap_mutex);
+		btrfs_end_transaction(trans);
+		return ret;
+	}
+
+	/* Try to reserve enough space for block. */
+
+	spin_lock(&sinfo->lock);
+	btrfs_space_info_update_bytes_may_use(sinfo, remap_length);
+	spin_unlock(&sinfo->lock);
+
+	if (is_data)
+		min_size = fs_info->sectorsize;
+	else
+		min_size = fs_info->nodesize;
+
+	/*
+	 * We're using btrfs_reserve_extent() to allocate a contiguous
+	 * logical address range, but this will become a remap item rather than
+	 * an extent in the extent tree.
+	 *
+	 * Short allocations are fine: it means that we chop off the beginning
+	 * of the identity remap that we're processing, and will tackle the
+	 * rest of it the next time round.
+	 */
+	ret = btrfs_reserve_extent(fs_info->fs_root, remap_length,
+				   remap_length, min_size,
+				   0, 0, &ins, is_data, false);
+	if (ret) {
+		spin_lock(&sinfo->lock);
+		btrfs_space_info_update_bytes_may_use(sinfo, -remap_length);
+		spin_unlock(&sinfo->lock);
+
+		mutex_unlock(&fs_info->remap_mutex);
+		btrfs_end_transaction(trans);
+		return ret;
+	}
+
+	made_reservation = true;
+
+	new_addr = ins.objectid;
+	length = ins.offset;
+
+	if (!is_data && !IS_ALIGNED(length, fs_info->nodesize)) {
+		u64 new_length = ALIGN_DOWN(length, fs_info->nodesize);
+
+		btrfs_free_reserved_extent(fs_info, new_addr + new_length,
+					   length - new_length, 0);
+
+		length = new_length;
+	}
+
+	dest_bg = btrfs_lookup_block_group(fs_info, new_addr);
+
+	mutex_lock(&dest_bg->free_space_lock);
+	bg_needs_free_space = test_bit(BLOCK_GROUP_FLAG_NEEDS_FREE_SPACE,
+				       &dest_bg->runtime_flags);
+	mutex_unlock(&dest_bg->free_space_lock);
+
+	if (bg_needs_free_space) {
+		ret = btrfs_add_block_group_free_space(trans, dest_bg);
+		if (ret)
+			goto fail;
+	}
+
+	ret = do_copy(fs_info, start, new_addr, length);
+	if (ret)
+		goto fail;
+
+	ret = btrfs_remove_from_free_space_tree(trans, new_addr, length);
+	if (ret)
+		goto fail;
+
+	ret = add_remap_entry(trans, path, src_bg, start, new_addr, length);
+	if (ret) {
+		btrfs_add_to_free_space_tree(trans, new_addr, length);
+		goto fail;
+	}
+
+	adjust_block_group_remap_bytes(trans, dest_bg, length);
+	btrfs_free_reserved_bytes(dest_bg, length, 0);
+
+	spin_lock(&sinfo->lock);
+	sinfo->bytes_readonly += length;
+	spin_unlock(&sinfo->lock);
+
+next:
+	if (dest_bg)
+		btrfs_put_block_group(dest_bg);
+
+	if (made_reservation)
+		btrfs_dec_block_group_reservations(fs_info, new_addr);
+
+	mutex_unlock(&fs_info->remap_mutex);
+
+	if (src_bg->identity_remap_count == 0) {
+		bool mark_fully_remapped = false;
+
+		spin_lock(&src_bg->lock);
+
+		if (!src_bg->fully_remapped) {
+			mark_fully_remapped = true;
+			src_bg->fully_remapped = true;
+		}
+
+		spin_unlock(&src_bg->lock);
+
+		if (mark_fully_remapped)
+			btrfs_mark_bg_fully_remapped(src_bg, trans);
+	}
+
+	ret = btrfs_end_transaction(trans);
+	if (ret)
+		return ret;
+
+	if (no_more)
+		return 1;
+
+	*last_start = start;
+
+	return 0;
+
+fail:
+	if (dest_bg)
+		btrfs_put_block_group(dest_bg);
+
+	btrfs_free_reserved_extent(fs_info, new_addr, length, 0);
+
+	mutex_unlock(&fs_info->remap_mutex);
+	btrfs_end_transaction(trans);
+
+	return ret;
+}
+
+static int do_remap_reloc(struct btrfs_fs_info *fs_info,
+			  struct btrfs_path *path, struct btrfs_block_group *bg)
+{
+	u64 last_start;
+	int ret;
+
+	last_start = bg->start;
+
+	while (true) {
+		ret = do_remap_reloc_trans(fs_info, bg, path, &last_start);
+		if (ret) {
+			if (ret == 1)
+				ret = 0;
+			break;
+		}
+	}
+
+	return ret;
+}
+
 int btrfs_translate_remap(struct btrfs_fs_info *fs_info, u64 *logical,
 			  u64 *length)
 {
@@ -5127,6 +5455,14 @@ int btrfs_relocate_block_group(struct btrfs_fs_info *fs_info, u64 group_start,
 		}
 
 		ret = start_block_group_remapping(fs_info, path, bg);
+		if (ret)
+			goto out;
+
+		ret = do_remap_reloc(fs_info, path, rc->block_group);
+		if (ret)
+			goto out;
+
+		btrfs_delete_unused_bgs(fs_info);
 	} else {
 		ret = do_nonremap_reloc(fs_info, verbose, rc);
 	}
-- 
2.51.0