Btrfs: Do snapshot deletion in smaller chunks.
Before, snapshot deletion was a single atomic unit. This caused considerable
lock contention and required an unbounded amount of space. Now,
the drop_progress field in the root item is used to indicate how far along
snapshot deletion is, and to resume where it left off.
Signed-off-by: Chris Mason <chris.mason@oracle.com>
diff --git a/fs/btrfs/ctree.c b/fs/btrfs/ctree.c
index 19a30b7..aa824e2 100644
--- a/fs/btrfs/ctree.c
+++ b/fs/btrfs/ctree.c
@@ -659,9 +659,16 @@
struct buffer_head *b;
struct buffer_head *cow_buf;
struct btrfs_node *c;
+ struct btrfs_root_item *root_item = &root->root_item;
int slot;
int ret;
int level;
+ u8 lowest_level = 0;
+
+ if (btrfs_root_refs(root_item) == 0 && root->ref_cows) {
+ lowest_level = root_item->drop_level;
+ WARN_ON(ins_len || cow);
+ }
WARN_ON(p->nodes[0] != NULL);
WARN_ON(!mutex_is_locked(&root->fs_info->fs_mutex));
@@ -718,6 +725,9 @@
slot = p->slots[level];
BUG_ON(btrfs_header_nritems(&c->header) == 1);
}
+ /* this is only true while dropping a snapshot */
+ if (level == lowest_level)
+ break;
b = read_tree_block(root, btrfs_node_blockptr(c, slot));
} else {
struct btrfs_leaf *l = (struct btrfs_leaf *)c;