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

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Date:	Tue, 23 Jun 2009 20:19:45 +0900 (JST)
From:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
To:	Jens Axboe <jens.axboe@...cle.com>
Cc:	kosaki.motohiro@...fujitsu.com,
	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.

Yes, I know current behavior is not perfectly optimal.
but I haven't seen it cause serious issue.

Then, I guess you have big degression workload, yes? if so, I hope to see it.


> > 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?

Hopefully both. honestly I haven't understand your main worryed issue.



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