btrfs: move out now unused BG from the reclaim list

[ Upstream commit a9f189716cf15913c453299d72f69c51a9b0f86b ]

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>
Signed-off-by: Sasha Levin <sashal@kernel.org>

diff --git a/fs/btrfs/block-group.c b/fs/btrfs/block-group.c
index d24cef671c1aa02b0fa05bd51f8cbe2437d3d0f0..4ca6828586af50fc6ff33f78fa71b031c42e08bd 100644 (file)
--- a/fs/btrfs/block-group.c
+++ b/fs/btrfs/block-group.c
@@ -1475,11 +1475,14 @@ 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);
 }