linux-kernel - Re: merging the per-bdi writeback patchset

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Message-ID: <20090623105645.GX31415@kernel.dk>
Date:	Tue, 23 Jun 2009 12:56:46 +0200
From:	Jens Axboe <jens.axboe@...cle.com>
To:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Linux Kernel <linux-kernel@...r.kernel.org>, hch@...radead.org
Subject: Re: merging the per-bdi writeback patchset

On Tue, Jun 23 2009, KOSAKI Motohiro wrote:
> Hi
> 
> > On Tue, Jun 23 2009, Andrew Morton wrote:
> > > On Tue, 23 Jun 2009 10:11:56 +0200 Jens Axboe <jens.axboe@...cle.com> wrote:
> > > 
> > > > Things are looking good for this patchset and it's been in -next for
> > > > almost a week without any reports of problems. So I'd like to merge it
> > > > for 2.6.31 if at all possible. Any objections?
> > > 
> > > erk.  I was rather expecting I'd have time to have a look at it all.
> > 
> > OK, we can wait if we have to, just trying to avoid having to keep this
> > fresh for one full cycle. I have posted this patchset 11 times though
> > over months, so it's not like it's a new piece of work :-)
> > 
> > > It's unclear to me actually _why_ the performance changes which were
> > > observed have actually occurred.  In fact it's a bit unclear (to me)
> > > why the patchset was written and what it sets out to achieve :(
> > 
> > It started out trying to get rid of the pdflush uneven writeout. If you
> > look at various pdflush intensive workloads, even on a single disk you
> > often have 5 or more pdflush threads working the same device. It's just
> > not optimal. Another issue was starvation with request allocation. Given
> > that pdflush does non-blocking writes (it has to, by design), pdflush
> > can potentially be starved if someone else is working the device.
> 
> Can you please make reproduce program and post mesurement result?
> I hope to mesure the same program on my box.

For which issue? Lumpy writeout can often be observed just by doing
buffered writes to a bunch of files.

> Plus, Can you please write more vervose patch description? your patch is a
> bit harder review.

OK, I can probably improve on that. Do you mean the general description
of the patchset, or some of the individual patches?

-- 
Jens Axboe

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