Btrfs: avoid tree log commit when there are no changes
rpm has a habit of running fdatasync when the file hasn't
changed. We already detect if a file hasn't been changed
in the current transaction but it might have been sent to
the tree-log in this transaction and not changed since
the last call to fsync.
In this case, we want to avoid a tree log sync, which includes
a number of synchronous writes and barriers. This commit
extends the existing tracking of the last transaction to change
a file to also track the last sub-transaction.
The end result is that rpm -ivh and -Uvh are roughly twice as fast,
and on par with ext3.
Signed-off-by: Chris Mason <chris.mason@oracle.com>
diff --git a/fs/btrfs/file.c b/fs/btrfs/file.c
index 53fb1c9..4599113e 100644
--- a/fs/btrfs/file.c
+++ b/fs/btrfs/file.c
@@ -1087,8 +1087,10 @@
btrfs_end_transaction(trans, root);
else
btrfs_commit_transaction(trans, root);
- } else {
+ } else if (ret != BTRFS_NO_LOG_SYNC) {
btrfs_commit_transaction(trans, root);
+ } else {
+ btrfs_end_transaction(trans, root);
}
}
if (file->f_flags & O_DIRECT) {
@@ -1138,6 +1140,13 @@
int ret = 0;
struct btrfs_trans_handle *trans;
+
+ /* we wait first, since the writeback may change the inode */
+ root->log_batch++;
+ /* the VFS called filemap_fdatawrite for us */
+ btrfs_wait_ordered_range(inode, 0, (u64)-1);
+ root->log_batch++;
+
/*
* check the transaction that last modified this inode
* and see if its already been committed
@@ -1145,6 +1154,11 @@
if (!BTRFS_I(inode)->last_trans)
goto out;
+ /*
+ * if the last transaction that changed this file was before
+ * the current transaction, we can bail out now without any
+ * syncing
+ */
mutex_lock(&root->fs_info->trans_mutex);
if (BTRFS_I(inode)->last_trans <=
root->fs_info->last_trans_committed) {
@@ -1154,13 +1168,6 @@
}
mutex_unlock(&root->fs_info->trans_mutex);
- root->log_batch++;
- filemap_fdatawrite(inode->i_mapping);
- btrfs_wait_ordered_range(inode, 0, (u64)-1);
- root->log_batch++;
-
- if (datasync && !(inode->i_state & I_DIRTY_PAGES))
- goto out;
/*
* ok we haven't committed the transaction yet, lets do a commit
*/
@@ -1189,14 +1196,18 @@
*/
mutex_unlock(&dentry->d_inode->i_mutex);
- if (ret > 0) {
- ret = btrfs_commit_transaction(trans, root);
- } else {
- ret = btrfs_sync_log(trans, root);
- if (ret == 0)
- ret = btrfs_end_transaction(trans, root);
- else
+ if (ret != BTRFS_NO_LOG_SYNC) {
+ if (ret > 0) {
ret = btrfs_commit_transaction(trans, root);
+ } else {
+ ret = btrfs_sync_log(trans, root);
+ if (ret == 0)
+ ret = btrfs_end_transaction(trans, root);
+ else
+ ret = btrfs_commit_transaction(trans, root);
+ }
+ } else {
+ ret = btrfs_end_transaction(trans, root);
}
mutex_lock(&dentry->d_inode->i_mutex);
out:
