btrfs: clean snapshots one by one

Each time pick one dead root from the list and let the caller know if
it's needed to continue. This should improve responsiveness during
umount and balance which at some point waits for cleaning all currently
queued dead roots.

A new dead root is added to the end of the list, so the snapshots
disappear in the order of deletion.

The snapshot cleaning work is now done only from the cleaner thread and the
others wake it if needed.

Signed-off-by: David Sterba <dsterba@suse.cz>
Signed-off-by: Josef Bacik <jbacik@fusionio.com>

1 files changed, 8 insertions, 0 deletions

diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
index 7505856df9f3..be09157ff91b 100644
--- a/fs/btrfs/extent-tree.c
+++ b/fs/btrfs/extent-tree.c
@@ -7286,6 +7286,8 @@ static noinline int walk_up_tree(struct btrfs_trans_handle *trans,
  * reference count by one. if update_ref is true, this function
  * also make sure backrefs for the shared block and all lower level
  * blocks are properly updated.
+ *
+ * If called with for_reloc == 0, may exit early with -EAGAIN
  */
 int btrfs_drop_snapshot(struct btrfs_root *root,
                          struct btrfs_block_rsv *block_rsv, int update_ref,
@@ -7386,6 +7388,12 @@ int btrfs_drop_snapshot(struct btrfs_root *root,
         wc->reada_count = BTRFS_NODEPTRS_PER_BLOCK(root);
 
         while (1) {
+                if (!for_reloc && btrfs_fs_closing(root->fs_info)) {
+                        pr_debug("btrfs: drop snapshot early exit\n");
+                        err = -EAGAIN;
+                        goto out_end_trans;
+                }
+
                 ret = walk_down_tree(trans, root, path, wc);
                 if (ret < 0) {
                         err = ret;