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

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Date:	Tue,  5 Aug 2008 11:31:47 +0200 (MEST)
From:	Andrea Righi <righi.andrea@...il.com>
To:	Hirokazu Takahashi <taka@...inux.co.jp>
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

Hirokazu Takahashi wrote:
> 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?

-Andrea
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