Commit 2a0f7f57 authored Oct 10, 2011 by Li Zefan Committed by Chris Mason Oct 10, 2011

Btrfs: fix recursive auto-defrag



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 <lizf@cn.fujitsu.com>
Signed-off-by: Chris Mason <chris.mason@oracle.com>

parent b6316429

fs/btrfs/ioctl.c

+7 −0

Original line number	Diff line number	Diff line
		@@ -1055,6 +1055,13 @@ 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