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authorYan, Zheng <zheng.yan@oracle.com>2009-09-21 15:55:59 -0400
committerChris Mason <chris.mason@oracle.com>2009-09-21 15:55:59 -0400
commit1c4850e21df8b441164d910bc611ef46a01d5d75 (patch)
treeaeccbf3495421d1343bbe08cb824ac1ae6764e43 /fs/btrfs/transaction.c
parentb917b7c3be50435fa8257591b964934e917f2d45 (diff)
Btrfs: speed up snapshot dropping
This patch contains two changes to avoid unnecessary tree block reads during snapshot dropping. First, check tree block's reference count and flags before reading the tree block. if reference count > 1 and there is no need to update backrefs, we can avoid reading the tree block. Second, save when snapshot was created in root_key.offset. we can compare block pointer's generation with snapshot's creation generation during updating backrefs. If a given block was created before snapshot was created, the snapshot can't be the tree block's owner. So we can avoid reading the block. Signed-off-by: Yan Zheng <zheng.yan@oracle.com> Signed-off-by: Chris Mason <chris.mason@oracle.com>
Diffstat (limited to 'fs/btrfs/transaction.c')
-rw-r--r--fs/btrfs/transaction.c3
1 files changed, 2 insertions, 1 deletions
diff --git a/fs/btrfs/transaction.c b/fs/btrfs/transaction.c
index 6ed6186f51c..94f816cb6e3 100644
--- a/fs/btrfs/transaction.c
+++ b/fs/btrfs/transaction.c
@@ -720,7 +720,8 @@ static noinline int create_pending_snapshot(struct btrfs_trans_handle *trans,
memcpy(new_root_item, &root->root_item, sizeof(*new_root_item));
key.objectid = objectid;
- key.offset = 0;
+ /* record when the snapshot was created in key.offset */
+ key.offset = trans->transid;
btrfs_set_key_type(&key, BTRFS_ROOT_ITEM_KEY);
old = btrfs_lock_root_node(root);