linux-kernel - Re: [PATCH 9/9] ext3: do not throttle metadata and journal IO

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Date:	Wed, 22 Apr 2009 10:21:53 +0900
From:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Cc:	Andrea Righi <righi.andrea@...il.com>, randy.dunlap@...cle.com,
	Carl Henrik Lunde <chlunde@...g.uio.no>,
	Jens Axboe <jens.axboe@...cle.com>, eric.rannaud@...il.com,
	Balbir Singh <balbir@...ux.vnet.ibm.com>,
	fernando@....ntt.co.jp, dradford@...ehost.com,
	Gui@...p1.linux-foundation.org, agk@...rceware.org,
	subrata@...ux.vnet.ibm.com, Paul Menage <menage@...gle.com>,
	Theodore Tso <tytso@....edu>, akpm@...ux-foundation.org,
	containers@...ts.linux-foundation.org,
	linux-kernel@...r.kernel.org, dave@...ux.vnet.ibm.com,
	matt@...ehost.com, roberto@...it.it, ngupta@...gle.com
Subject: Re: [PATCH 9/9] ext3: do not throttle metadata and journal IO

On Wed, 22 Apr 2009 09:33:49 +0900
KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com> wrote:


> > And this should be probably strictly connected to the IO controller. If
> > we throttle or delay the dispatching/submission of some IO requests
> > without throttling the dirty pages rate a cgroup could completely waste
> > its own available memory with dirty (hard and slow to reclaim) pages.
> > 
> > That is in part the approach I used in io-throttle v12, adding a hook in
> > balance_dirty_pages_ratelimited_nr() to throttle the current task when
> > cgroup's IO limit are exceeded. Argh!
> > 
> > So, another proposal could be to re-add in io-throttle v14 the old hook
> > also in balance_dirty_pages_ratelimited_nr().
> > 
> > In this way io-throttle would:
> > 
> > - use page_cgroup infrastructure and page_cgroup->flags to encode the
> >   cgroup id that firstly dirtied a generic page
> > - account and opportunely throttle sync and writeback IO requests in
> >   submit_bio()
> > - at the same time throttle the tasks in
> >   balance_dirty_pages_ratelimited_nr() if the cgroup they belong has
> >   exhausted the IO BW (or quota, share, etc. in case of proportional BW
> >   limit)
> > 
> 
> IMHO, io-controller should just work as I/O subsystem as bdi. Now, per-bdi dirty_ratio
> is suppoted and it seems to work well.  
> 
> Can't we write a function like  bdi_writeout_fraction() ?;
> It will be a simple choice.
> 
One more thing, if you want dirty_ratio for throttoling I/O not for supporing page reclaim,
Something like task_dirty_limit() will be apporpriate.

Thanks,
-Kame

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