btrfs: move out now unused BG from the reclaim list

An unused block group is easy to remove to free up space and should be
reclaimed fast. Such block group can often already be a target of the
reclaim process. As we check list_empty(&bg->bg_list), we keep it in the
reclaim list. That block group is never reclaimed until the file system
is filled e.g. up to 75%.

Instead, we can move unused block group to the unused list and delete it
fast.

Fixes: 18bb8bbf13c1 ("btrfs: zoned: automatically reclaim zones")
CC: stable@vger.kernel.org # 5.15+
Reviewed-by: Filipe Manana <fdmanana@suse.com>
Reviewed-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Signed-off-by: Naohiro Aota <naohiro.aota@wdc.com>
Signed-off-by: David Sterba <dsterba@suse.com>

diff --git a/fs/btrfs/block-group.c b/fs/btrfs/block-group.c
index 18305f5c74c9318279d965a302b5f4279aa881d2..616507596671f20d83d7db98069761130b8fe5f1 100644 (file)
--- a/fs/btrfs/block-group.c
+++ b/fs/btrfs/block-group.c
@@ -1633,11 +1633,14 @@ void btrfs_mark_bg_unused(struct btrfs_block_group *bg)
 {
        struct btrfs_fs_info *fs_info = bg->fs_info;
 
+       trace_btrfs_add_unused_block_group(bg);
        spin_lock(&fs_info->unused_bgs_lock);
        if (list_empty(&bg->bg_list)) {
                btrfs_get_block_group(bg);
-               trace_btrfs_add_unused_block_group(bg);
                list_add_tail(&bg->bg_list, &fs_info->unused_bgs);
+       } else {
+               /* Pull out the block group from the reclaim_bgs list. */
+               list_move_tail(&bg->bg_list, &fs_info->unused_bgs);
        }
        spin_unlock(&fs_info->unused_bgs_lock);
 }