From: Filipe Manana <fdmanana@suse.com>
Date: Thu, 29 Jul 2021 18:52:46 +0100
Git-commit: 8be2ba2e0e11ade6ab96d8887dbb12abbd3540f4
Patch-mainline: v5.15-rc1
References: bsc#1197915
Subject: [PATCH] btrfs: avoid unnecessarily logging directories that had no
changes
There are several cases where when logging an inode we need to log its
parent directories or logging subdirectories when logging a directory.
There are cases however where we end up logging a directory even if it was
not changed in the current transaction, no dentries added or removed since
the last transaction. While this is harmless from a functional point of
view, it is a waste time as it brings no advantage.
One example where this is triggered is the following:
$ mkfs.btrfs -f /dev/sdc
$ mount /dev/sdc /mnt
$ mkdir /mnt/A
$ mkdir /mnt/B
$ mkdir /mnt/C
$ touch /mnt/A/foo
$ ln /mnt/A/foo /mnt/B/bar
$ ln /mnt/A/foo /mnt/C/baz
$ sync
$ rm -f /mnt/A/foo
$ xfs_io -c "fsync" /mnt/B/bar
This last fsync ends up logging directories A, B and C, however we only
need to log directory A, as B and C were not changed since the last
transaction commit.
So fix this by changing need_log_inode(), to return false in case the
given inode is a directory and has a ->last_trans value smaller than the
current transaction's ID.
Signed-off-by: Filipe Manana <fdmanana@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
---
fs/btrfs/tree-log.c | 7 +++++++
1 file changed, 7 insertions(+)
diff --git a/fs/btrfs/tree-log.c b/fs/btrfs/tree-log.c
index 1ce7e4480256..a1aaa1b8bd5c 100644
--- a/fs/btrfs/tree-log.c
+++ b/fs/btrfs/tree-log.c
@@ -5613,6 +5613,13 @@ static int btrfs_log_inode(struct btrfs_trans_handle *trans,
static bool need_log_inode(struct btrfs_trans_handle *trans,
struct btrfs_inode *inode)
{
+ /*
+ * If a directory was not modified, no dentries added or removed, we can
+ * and should avoid logging it.
+ */
+ if (S_ISDIR(inode->vfs_inode.i_mode) && inode->last_trans < trans->transid)
+ return false;
+
/*
* If this inode does not have new/updated/deleted xattrs since the last
* time it was logged and is flagged as logged in the current transaction,
--
2.26.2