Btrfs: Find and remove dead roots the first time a root is loaded.

Dead roots are trees left over after a crash, and they were either in the
process of being removed or were waiting to be removed when the box crashed.
Before, a search of the entire tree of root pointers was done on mount
looking for dead roots.  Now, the search is done the first time we load
a root.

This makes mount faster when there are a large number of snapshots, and it
enables the block accounting code to properly update the block counts on
the latest root as old versions of the root are reaped after a crash.

Signed-off-by: Chris Mason <chris.mason@oracle.com>

1 files changed, 13 insertions, 3 deletions

diff --git a/fs/btrfs/root-tree.c b/fs/btrfs/root-tree.c
index 402f67821c14..3b5926dfbeba 100644
--- a/fs/btrfs/root-tree.c
+++ b/fs/btrfs/root-tree.c
@@ -93,7 +93,8 @@ int btrfs_insert_root(struct btrfs_trans_handle *trans, struct btrfs_root
         return ret;
 }
 
-int btrfs_find_dead_roots(struct btrfs_root *root)
+int btrfs_find_dead_roots(struct btrfs_root *root, u64 objectid,
+                          struct btrfs_root *latest)
 {
         struct btrfs_root *dead_root;
         struct btrfs_item *item;
@@ -105,7 +106,7 @@ int btrfs_find_dead_roots(struct btrfs_root *root)
         struct btrfs_leaf *leaf;
         int slot;
 
-        key.objectid = 0;
+        key.objectid = objectid;
         key.flags = 0;
         btrfs_set_key_type(&key, BTRFS_ROOT_ITEM_KEY);
         key.offset = 0;
@@ -131,15 +132,24 @@ int btrfs_find_dead_roots(struct btrfs_root *root)
                 btrfs_disk_key_to_cpu(&key, &item->key);
                 if (btrfs_key_type(&key) != BTRFS_ROOT_ITEM_KEY)
                         goto next;
+
+                if (key.objectid < objectid)
+                        goto next;
+
+                if (key.objectid > objectid)
+                        break;
+
                 ri = btrfs_item_ptr(leaf, slot, struct btrfs_root_item);
                 if (btrfs_root_refs(ri) != 0)
                         goto next;
+
                 dead_root = btrfs_read_fs_root_no_radix(root->fs_info, &key);
                 if (IS_ERR(dead_root)) {
                         ret = PTR_ERR(dead_root);
                         goto err;
                 }
-                ret = btrfs_add_dead_root(dead_root,
+
+                ret = btrfs_add_dead_root(dead_root, latest,
                                           &root->fs_info->dead_roots);
                 if (ret)
                         goto err;