[PATCH v2 3/3] btrfs: Don't set SHAREABLE flag for data reloc tree

[Qu Wenruo <wqu@suse.com>]

SHAREABLE flag is set for subvolumes because users can create snapshot
for subvolumes, thus sharing tree blocks of them.

But data reloc tree are not exposed to user space, as it's only an
internal tree for data relocation, thus it doesn't need the full path
replacement treat at all.

This patch will make data reloc tree just a non-shareable tree, and add
btrfs_fs_info::data_reloc_root for data reloc tree, so relocation code can
grab it from fs_info directly.

This would slightly improve tree relocation, as now data reloc tree
can go through regular COW routine to get relocated, without bothering
the complex tree reloc tree routine.

Signed-off-by: Qu Wenruo <wqu@suse.com>
---
 fs/btrfs/ctree.h      |  1 +
 fs/btrfs/disk-io.c    | 14 +++++++++++++-
 fs/btrfs/relocation.c | 17 ++++++-----------
 3 files changed, 20 insertions(+), 12 deletions(-)

diff --git a/fs/btrfs/ctree.h b/fs/btrfs/ctree.h
index 65c09aea4cb9..d3be34316677 100644
--- a/fs/btrfs/ctree.h
+++ b/fs/btrfs/ctree.h
@@ -582,6 +582,7 @@ struct btrfs_fs_info {
 	struct btrfs_root *quota_root;
 	struct btrfs_root *uuid_root;
 	struct btrfs_root *free_space_root;
+	struct btrfs_root *data_reloc_root;
 
 	/* the log root tree is a directory of all the other log roots */
 	struct btrfs_root *log_root_tree;
diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
index 76b165ad497f..fced949b150c 100644
--- a/fs/btrfs/disk-io.c
+++ b/fs/btrfs/disk-io.c
@@ -1419,7 +1419,8 @@ static int btrfs_init_fs_root(struct btrfs_root *root)
 	if (ret)
 		goto fail;
 
-	if (root->root_key.objectid != BTRFS_TREE_LOG_OBJECTID) {
+	if (root->root_key.objectid != BTRFS_TREE_LOG_OBJECTID &&
+	    root->root_key.objectid != BTRFS_DATA_RELOC_TREE_OBJECTID) {
 		set_bit(BTRFS_ROOT_SHAREABLE, &root->state);
 		btrfs_check_and_init_root_item(&root->root_item);
 	}
@@ -1525,6 +1526,7 @@ void btrfs_free_fs_info(struct btrfs_fs_info *fs_info)
 	btrfs_put_root(fs_info->uuid_root);
 	btrfs_put_root(fs_info->free_space_root);
 	btrfs_put_root(fs_info->fs_root);
+	btrfs_put_root(fs_info->data_reloc_root);
 	btrfs_check_leaked_roots(fs_info);
 	btrfs_extent_buffer_leak_debug_check(fs_info);
 	kfree(fs_info->super_copy);
@@ -1981,6 +1983,7 @@ static void free_root_pointers(struct btrfs_fs_info *info, bool free_chunk_root)
 	free_root_extent_buffers(info->quota_root);
 	free_root_extent_buffers(info->uuid_root);
 	free_root_extent_buffers(info->fs_root);
+	free_root_extent_buffers(info->data_reloc_root);
 	if (free_chunk_root)
 		free_root_extent_buffers(info->chunk_root);
 	free_root_extent_buffers(info->free_space_root);
@@ -2287,6 +2290,15 @@ static int btrfs_read_roots(struct btrfs_fs_info *fs_info)
 	set_bit(BTRFS_ROOT_TRACK_DIRTY, &root->state);
 	fs_info->csum_root = root;
 
+	location.objectid = BTRFS_DATA_RELOC_TREE_OBJECTID;
+	root = btrfs_get_fs_root(fs_info, &location, true);
+	if (IS_ERR(root)) {
+		ret = PTR_ERR(root);
+		goto out;
+	}
+	set_bit(BTRFS_ROOT_TRACK_DIRTY, &root->state);
+	fs_info->data_reloc_root = root;
+
 	location.objectid = BTRFS_QUOTA_TREE_OBJECTID;
 	root = btrfs_read_tree_root(tree_root, &location);
 	if (!IS_ERR(root)) {
diff --git a/fs/btrfs/relocation.c b/fs/btrfs/relocation.c
index 437b782c57e6..9afc1a6928cf 100644
--- a/fs/btrfs/relocation.c
+++ b/fs/btrfs/relocation.c
@@ -3470,14 +3470,12 @@ struct inode *create_reloc_inode(struct btrfs_fs_info *fs_info,
 {
 	struct inode *inode = NULL;
 	struct btrfs_trans_handle *trans;
-	struct btrfs_root *root;
+	struct btrfs_root *root = btrfs_grab_root(fs_info->data_reloc_root);
 	struct btrfs_key key;
 	u64 objectid;
 	int err = 0;
 
-	root = read_fs_root(fs_info, BTRFS_DATA_RELOC_TREE_OBJECTID);
-	if (IS_ERR(root))
-		return ERR_CAST(root);
+	ASSERT(root);
 
 	trans = btrfs_start_transaction(root, 6);
 	if (IS_ERR(trans)) {
@@ -3870,13 +3868,10 @@ int btrfs_recover_relocation(struct btrfs_root *root)
 
 	if (err == 0) {
 		/* cleanup orphan inode in data relocation tree */
-		fs_root = read_fs_root(fs_info, BTRFS_DATA_RELOC_TREE_OBJECTID);
-		if (IS_ERR(fs_root)) {
-			err = PTR_ERR(fs_root);
-		} else {
-			err = btrfs_orphan_cleanup(fs_root);
-			btrfs_put_root(fs_root);
-		}
+		fs_root = btrfs_grab_root(fs_info->data_reloc_root);
+		ASSERT(fs_root);
+		err = btrfs_orphan_cleanup(fs_root);
+		btrfs_put_root(fs_root);
 	}
 	return err;
 }
-- 
2.26.2