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>

5 files changed, 25 insertions, 12 deletions

diff --git a/fs/btrfs/ctree.h b/fs/btrfs/ctree.h
index 03e1c4ad341b..6d6e94b63803 100644
--- a/fs/btrfs/ctree.h
+++ b/fs/btrfs/ctree.h
@@ -1148,7 +1148,8 @@ int btrfs_update_root(struct btrfs_trans_handle *trans, struct btrfs_root
                       *item);
 int btrfs_find_last_root(struct btrfs_root *root, u64 objectid, struct
                          btrfs_root_item *item, struct btrfs_key *key);
-int btrfs_find_dead_roots(struct btrfs_root *root);
+int btrfs_find_dead_roots(struct btrfs_root *root, u64 objectid,
+                          struct btrfs_root *latest_root);
 /* dir-item.c */
 int btrfs_insert_dir_item(struct btrfs_trans_handle *trans, struct btrfs_root
                           *root, const char *name, int name_len, u64 dir,
diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
index 6c953a0e0aa3..4296839eea1a 100644
--- a/fs/btrfs/disk-io.c
+++ b/fs/btrfs/disk-io.c
@@ -426,6 +426,10 @@ struct btrfs_root *btrfs_read_fs_root(struct btrfs_fs_info *fs_info,
                 return ERR_PTR(ret);
         }
 
+        ret = btrfs_find_dead_roots(fs_info->tree_root,
+                                    root->root_key.objectid, root);
+        BUG_ON(ret);
+
         return root;
 }
 
@@ -522,11 +526,6 @@ struct btrfs_root *open_ctree(struct super_block *sb)
         btrfs_read_block_groups(extent_root);
 
         fs_info->generation = btrfs_super_generation(disk_super) + 1;
-        ret = btrfs_find_dead_roots(tree_root);
-        if (ret) {
-                mutex_unlock(&fs_info->fs_mutex);
-                goto fail_tree_root;
-        }
         mutex_unlock(&fs_info->fs_mutex);
         return tree_root;
 
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;
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;
diff --git a/fs/btrfs/transaction.h b/fs/btrfs/transaction.h
index e451783a1a4d..4bc328cbb24c 100644
--- a/fs/btrfs/transaction.h
+++ b/fs/btrfs/transaction.h
@@ -78,7 +78,8 @@ void btrfs_transaction_flush_work(struct btrfs_root *root);
 void btrfs_transaction_queue_work(struct btrfs_root *root, int delay);
 void btrfs_init_transaction_sys(void);
 void btrfs_exit_transaction_sys(void);
-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);
 int btrfs_defrag_dirty_roots(struct btrfs_fs_info *info);
 int btrfs_defrag_root(struct btrfs_root *root, int cacheonly);
 int btrfs_clean_old_snapshots(struct btrfs_root *root);