From: Chris Mason <chris.mason@oracle.com>
To: Li Zefan <lizf@cn.fujitsu.com>
Cc: "linux-btrfs@vger.kernel.org" <linux-btrfs@vger.kernel.org>
Subject: Re: [PATCH] Btrfs: fix recursive auto-defrag
Date: Thu, 6 Oct 2011 11:53:34 -0400 [thread overview]
Message-ID: <20111006155334.GC5716@shiny.elevennetworks.com> (raw)
In-Reply-To: <4E8D230A.4040801@cn.fujitsu.com>
On Thu, Oct 06, 2011 at 11:39:54AM +0800, Li Zefan wrote:
> 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.
Really nice and small fix. I'll definitely send this for 3.1
-chris
prev parent reply other threads:[~2011-10-06 15:53 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-10-06 3:39 [PATCH] Btrfs: fix recursive auto-defrag Li Zefan
2011-10-06 14:14 ` David Sterba
2011-10-06 15:53 ` Chris Mason [this message]
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