linux-kernel - Re: Too many I/O controller patches

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Date:	Tue, 05 Aug 2008 19:01:13 +0900 (JST)
From:	Hirokazu Takahashi <taka@...inux.co.jp>
To:	righi.andrea@...il.com
Cc:	dave@...ux.vnet.ibm.com, xen-devel@...ts.xensource.com,
	containers@...ts.linux-foundation.org,
	linux-kernel@...r.kernel.org,
	virtualization@...ts.linux-foundation.org, dm-devel@...hat.com,
	agk@...rceware.org
Subject: Re: Too many I/O controller patches

Hi,

> > Hi, Andrea,
> > 
> > I'm working with Ryo on dm-ioband and other stuff.
> > 
> >>> On Mon, 2008-08-04 at 20:22 +0200, Andrea Righi wrote:
> >>>> But I'm not yet convinced that limiting the IO writes at the device
> >>>> mapper layer is the best solution. IMHO it would be better to throttle
> >>>> applications' writes when they're dirtying pages in the page cache (the
> >>>> io-throttle way), because when the IO requests arrive to the device
> >>>> mapper it's too late (we would only have a lot of dirty pages that are
> >>>> waiting to be flushed to the limited block devices, and maybe this could
> >>>> lead to OOM conditions). IOW dm-ioband is doing this at the wrong level
> >>>> (at least for my requirements). Ryo, correct me if I'm wrong or if I've
> >>>> not understood the dm-ioband approach.
> >>> The avoid-lots-of-page-dirtying problem sounds like a hard one.  But, if
> >>> you look at this in combination with the memory controller, they would
> >>> make a great team.
> >>>
> >>> The memory controller keeps you from dirtying more than your limit of
> >>> pages (and pinning too much memory) even if the dm layer is doing the
> >>> throttling and itself can't throttle the memory usage.
> >> mmh... but in this way we would just move the OOM inside the cgroup,
> >> that is a nice improvement, but the main problem is not resolved...
> > 
> > The concept of dm-ioband includes it should be used with cgroup memory
> > controller as well as the bio cgroup. The memory controller is supposed
> > to control memory allocation and dirty-page ratio inside each cgroup.
> > 
> > Some guys of cgroup memory controller team just started to implement
> > the latter mechanism. They try to make each cgroup have a threshold
> > to limit the number of dirty pages in the group.
> 
> Interesting, they also post a patch or RFC?

You can take a look at the thread start from
http://www.ussg.iu.edu/hypermail/linux/kernel/0807.1/0472.html,
whose subject is "[PATCH][RFC] dirty balancing for cgroups."

This project has just started, so it would be a good time to
discuss it with them.

Thanks,
Hirokazu Takahashi.

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