linux-kernel - Re: high iowait problem(Bug 12309 on bugzilla.kernel.org)

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Message-Id: <20100419143102.38f37fe9.akpm@linux-foundation.org>
Date:	Mon, 19 Apr 2010 14:31:02 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Steven B <damentz@...il.com>
Cc:	Frank Ren <frankrq2009@....com>, mingo <mingo@...e.hu>,
	"a.p.zijlstra" <a.p.zijlstra@...llo.nl>,
	"jens.axboe" <jens.axboe@...cle.com>, linux-kernel@...r.kernel.org,
	stable@...nel.org, dm-devel@...hat.com,
	Alasdair G Kergon <agk@...hat.com>,
	"Martin K. Petersen" <martin.petersen@...cle.com>
Subject: Re: high iowait problem(Bug 12309 on bugzilla.kernel.org)

On Thu, 15 Apr 2010 00:58:05 -0500
Steven B <damentz@...il.com> wrote:

> Hi Andrew,
> 
> > So something between 2.6.32.3 and 2.6.32.8 inclusive rebroke the
> > kernel. __That's useful info.
> >
> > Looking at the changelogs, the only thing I can immediately see in the
> > block-core area is
> >
> > : commit cb723ba5d03bf719dbc7409b4d67572d4472ef8b
> > : Author: Dmitry Monakhov <dmonakhov@...nvz.org>
> > : Date: __ Wed Jan 27 22:44:36 2010 +0300
> > :
> > : __ __ block: fix bio_add_page for non trivial merge_bvec_fn case
> >
> > which seems unlikely.
> >
> > I'm seeing just one device-mapper change whcih went in over that
> > timeframe:
> >
> > : commit e0f5cfa7c18b411634e73923841eccd3a4c0ce7f
> > : Author: Martin K. Petersen <martin.petersen@...cle.com>
> > : Date: __ Mon Jan 11 03:21:50 2010 -0500
> > :
> > : __ __ DM: Fix device mapper topology stacking
> >
> >
> 
> Although I can't provide any big details, I went through the commits between
> 2.6.32.2 and 2.6.32.8 and as many things that could affect IO and reverted
> them from my 2.6.33.2 kernel.
> 
> Here's my list of commits I reverted that seemed to improve performance locally
> running a 2.6.33.2 kernel.
> 
> cb723ba5d03bf719dbc7409b4d67572d4472ef8b (this one you suspected)
> block: fix bio_add_page for non trivial merge_bvec_fn case
> 
> b2ea8cb9c8f1937cb80b9beb50548a05bfc37819
> vmscan: do not evict inactive pages when skipping an active list scan
> 
> e4dd8ca5be771aa706b0797b3284328bb595bfa1
> fasync: split 'fasync_helper()' into separate add/remove functions
> 
> Though, I was hoping you guys could identify which one of these is
> the real culprit.

Can you go through and revert them individually please?
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