linux-kernel - Re: 2.6.36 io bring the system to its knees

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Message-Id: <1289401148-sup-3632@think>
Date:	Wed, 10 Nov 2010 10:00:36 -0500
From:	Chris Mason <chris.mason@...cle.com>
To:	Christoph Hellwig <hch@...radead.org>
Cc:	Theodore Tso <tytso@....edu>, Dave Chinner <david@...morbit.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Jens Axboe <axboe@...nel.dk>, dave b <db.pub.mail@...il.com>,
	Sanjoy Mahajan <sanjoy@...n.edu>,
	Jesper Juhl <jj@...osbits.net>, Ingo Molnar <mingo@...e.hu>,
	Pekka Enberg <penberg@...nel.org>,
	Aidar Kultayev <the.aidar@...il.com>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	linux-mm <linux-mm@...ck.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Nick Piggin <npiggin@...e.de>,
	Arjan van de Ven <arjan@...radead.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Corrado Zoccolo <czoccolo@...il.com>,
	Shaohua Li <shaohua.li@...el.com>,
	Steven Barrett <damentz@...il.com>
Subject: Re: 2.6.36 io bring the system to its knees

Excerpts from Christoph Hellwig's message of 2010-11-10 09:57:12 -0500:
> On Wed, Nov 10, 2010 at 09:33:29AM -0500, Theodore Tso wrote:
> > The chance that this occurs using data=writeback in ext4 is much less, BTW, because with delayed allocation we delay updating the inode until right before we write the block.  I have a plan for changing things so that we write the data blocks *first* and then update the metadata blocks second, which will mean that ext4 data=ordered will go away entirely, and we'll get both the safety and as well as avoiding the forced data page writeouts during journal commits.
> 
> That's the scheme used by XFS and btrfs in one form or another.  Chris
> also had a patch to implement it for ext3, which unfortunately fell
> under the floor.

It probably still applies, but by the time I had it stable I realized
that ext4 was really a better place to fix this stuff.  ext3 is what it
is (good and bad), and a big change like my data=guarded code probably
isn't the best way to help.

-chris
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