From 2a0f7f5769992bae5b3f97157fd80b2b943be485 Mon Sep 17 00:00:00 2001
From: Li Zefan <lizf@cn.fujitsu.com>
Date: Mon, 10 Oct 2011 15:43:34 -0400
Subject: [PATCH] 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>
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