From mboxrd@z Thu Jan 1 00:00:00 1970 From: Li Zefan Subject: [PATCH] Btrfs: fix recursive auto-defrag Date: Thu, 06 Oct 2011 11:39:54 +0800 Message-ID: <4E8D230A.4040801@cn.fujitsu.com> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 To: "linux-btrfs@vger.kernel.org" Return-path: List-ID: Follow those steps: # mount -o autodefrag /dev/sda7 /mnt # dd if=/dev/urandom of=/mnt/tmp bs=200K count=1 # sync # dd if=/dev/urandom of=/mnt/tmp bs=8K count=1 conv=notrunc and then it'll go into a loop: writeback -> defrag -> writeback ... It's because writeback writes [8K, 200K] and then writes [0, 8K]. I tried to make writeback know if the pages are dirtied by defrag, but the patch was a bit intrusive. Here I simply set writeback_index when we defrag a file. Signed-off-by: Li Zefan --- fs/btrfs/ioctl.c | 7 +++++++ 1 files changed, 7 insertions(+), 0 deletions(-) diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c index 970977a..7a10f94 100644 --- a/fs/btrfs/ioctl.c +++ b/fs/btrfs/ioctl.c @@ -1047,6 +1047,13 @@ int btrfs_defrag_file(struct inode *inode, struct file *file, if (!max_to_defrag) max_to_defrag = last_index - 1; + /* + * make writeback starts from i, so the defrag range can be + * written sequentially. + */ + if (i < inode->i_mapping->writeback_index) + inode->i_mapping->writeback_index = i; + while (i <= last_index && defrag_count < max_to_defrag) { /* * make sure we stop running if someone unmounts -- 1.7.3.1