linux-kernel - Re: notes on volatile write caches vs fdatasync

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Message-ID: <4A96DDE0.9090306@garzik.org>
Date:	Thu, 27 Aug 2009 15:26:24 -0400
From:	Jeff Garzik <jeff@...zik.org>
To:	Christoph Hellwig <hch@....de>
CC:	Jan Kara <jack@...e.cz>, linux-fsdevel@...r.kernel.org,
	linux-kernel@...r.kernel.org, chris.mason@...cle.com,
	tytso@....edu, adilger@....com, swhiteho@...hat.com,
	konishi.ryusuke@....ntt.co.jp, mfasheh@...e.com,
	joel.becker@...cle.com
Subject: Re: notes on volatile write caches vs fdatasync

On 08/27/2009 02:49 PM, Christoph Hellwig wrote:
> On Thu, Aug 27, 2009 at 03:02:52PM +0200, Jan Kara wrote:
>>    I've noticed this as well when we were tracking some problems Pavel
>> Machek found with his USB stick. I even wrote a patch at the time
>>    http://osdir.com/ml/linux-ext4/2009-01/msg00015.html
>> but it somehow died out. Now, the situation should be simpler with
>> fsync paths cleaned up... BTW: People wanted this to be configurable per
>> block device which probably makes sence...
>
> Yeah, that patch is pretty ugly.  We need to do these cache flushes
> in ->fsync (and ->sync_fs if any filesystem really doesn't guarantee to
> issue  transaction there after data has been written).  Adding it
> to simple_fsync too sounds good to me.

Agreed.  That was the direction I was heading with my patch[1].  Last 
feedback I got on that was needing to add a knob to optionally disable 
this new cache-flush behavior.

	Jeff



[1] http://lkml.org/lkml/2009/3/27/366
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