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, 4 insertions, 2 deletions

diff --git a/fs/btrfs/transaction.c b/fs/btrfs/transaction.c
index 2b15daa3a9f2..29755593de65 100644
--- a/fs/btrfs/transaction.c
+++ b/fs/btrfs/transaction.c
@@ -239,7 +239,9 @@ struct dirty_root {
         struct btrfs_root *latest_root;
 };
 
-int btrfs_add_dead_root(struct btrfs_root *root, struct list_head *dead_list)
+int btrfs_add_dead_root(struct btrfs_root *root,
+                        struct btrfs_root *latest,
+                        struct list_head *dead_list)
 {
         struct dirty_root *dirty;
 
@@ -247,6 +249,7 @@ int btrfs_add_dead_root(struct btrfs_root *root, struct list_head *dead_list)
         if (!dirty)
                 return -ENOMEM;
         dirty->root = root;
+        dirty->latest_root = latest;
         list_add(&dirty->list, dead_list);
         return 0;
 }
@@ -412,7 +415,6 @@ static int drop_dirty_roots(struct btrfs_root *tree_root,
 
                 while(1) {
                         trans = btrfs_start_transaction(tree_root, 1);
-
                         ret = btrfs_drop_snapshot(trans, dirty->root);
                         if (ret != -EAGAIN) {
                                 break;