[PATCH] btrfs: relocation: Remove is_cowonly_root()

[PATCH] btrfs: relocation: Remove is_cowonly_root()

[Qu Wenruo]

This function is only used in read_fs_root(), which is just a wrapper of
btrfs_get_fs_root().

For all the mentioned essential roots except log root tree,
btrfs_get_fs_root() has its own quick path to grab them from fs_info
directly, thus no need for key.offset modification.

For subvolume trees, btrfs_get_fs_root() with key.offset == -1 is
completely fine.

For log trees and log root tree, it's impossible to hit them, as for
relocation all backrefs are fetched from commit root, which never
records log tree blocks.

Log tree blocks either get freed in regular transaction commit, or
replayed at mount time. At runtime we should never hit an backref for
log tree in extent tree.

Signed-off-by: Qu Wenruo <wqu@suse.com>
---
 fs/btrfs/relocation.c | 20 +-------------------
 1 file changed, 1 insertion(+), 19 deletions(-)

diff --git a/fs/btrfs/relocation.c b/fs/btrfs/relocation.c
index 9c68c0e42898..207442557ac4 100644
--- a/fs/btrfs/relocation.c
+++ b/fs/btrfs/relocation.c
@@ -505,21 +505,6 @@ static struct btrfs_root *find_reloc_root(struct reloc_control *rc,
 	return root;
 }
 
-static int is_cowonly_root(u64 root_objectid)
-{
-	if (root_objectid == BTRFS_ROOT_TREE_OBJECTID ||
-	    root_objectid == BTRFS_EXTENT_TREE_OBJECTID ||
-	    root_objectid == BTRFS_CHUNK_TREE_OBJECTID ||
-	    root_objectid == BTRFS_DEV_TREE_OBJECTID ||
-	    root_objectid == BTRFS_TREE_LOG_OBJECTID ||
-	    root_objectid == BTRFS_CSUM_TREE_OBJECTID ||
-	    root_objectid == BTRFS_UUID_TREE_OBJECTID ||
-	    root_objectid == BTRFS_QUOTA_TREE_OBJECTID ||
-	    root_objectid == BTRFS_FREE_SPACE_TREE_OBJECTID)
-		return 1;
-	return 0;
-}
-
 static struct btrfs_root *read_fs_root(struct btrfs_fs_info *fs_info,
 					u64 root_objectid)
 {
@@ -527,10 +512,7 @@ static struct btrfs_root *read_fs_root(struct btrfs_fs_info *fs_info,
 
 	key.objectid = root_objectid;
 	key.type = BTRFS_ROOT_ITEM_KEY;
-	if (is_cowonly_root(root_objectid))
-		key.offset = 0;
-	else
-		key.offset = (u64)-1;
+	key.offset = (u64)-1;
 
 	return btrfs_get_fs_root(fs_info, &key, false);
 }
-- 
2.25.0

Re: [PATCH] btrfs: relocation: Remove is_cowonly_root()

[Josef Bacik]

On 2/12/20 2:43 AM, Qu Wenruo wrote:
> This function is only used in read_fs_root(), which is just a wrapper of
> btrfs_get_fs_root().
> 
> For all the mentioned essential roots except log root tree,
> btrfs_get_fs_root() has its own quick path to grab them from fs_info
> directly, thus no need for key.offset modification.
> 
> For subvolume trees, btrfs_get_fs_root() with key.offset == -1 is
> completely fine.
> 
> For log trees and log root tree, it's impossible to hit them, as for
> relocation all backrefs are fetched from commit root, which never
> records log tree blocks.
> 
> Log tree blocks either get freed in regular transaction commit, or
> replayed at mount time. At runtime we should never hit an backref for
> log tree in extent tree.
> 
> Signed-off-by: Qu Wenruo <wqu@suse.com>

Reviewed-by: Josef Bacik <josef@toxicpanda.com>

Thanks,

Josef

Re: [PATCH] btrfs: relocation: Remove is_cowonly_root()

[David Sterba]

On Wed, Feb 12, 2020 at 03:43:31PM +0800, Qu Wenruo wrote:
> This function is only used in read_fs_root(), which is just a wrapper of
> btrfs_get_fs_root().
> 
> For all the mentioned essential roots except log root tree,
> btrfs_get_fs_root() has its own quick path to grab them from fs_info
> directly, thus no need for key.offset modification.
> 
> For subvolume trees, btrfs_get_fs_root() with key.offset == -1 is
> completely fine.
> 
> For log trees and log root tree, it's impossible to hit them, as for
> relocation all backrefs are fetched from commit root, which never
> records log tree blocks.
> 
> Log tree blocks either get freed in regular transaction commit, or
> replayed at mount time. At runtime we should never hit an backref for
> log tree in extent tree.
> 
> Signed-off-by: Qu Wenruo <wqu@suse.com>

Added to misc-next, thanks.