linux-kernel - Re: [ckrm-tech] RFC: Memory Controller

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Message-ID: <45471510.4070407@in.ibm.com>
Date:	Tue, 31 Oct 2006 14:49:12 +0530
From:	Balbir Singh <balbir@...ibm.com>
To:	Pavel Emelianov <xemul@...nvz.org>
CC:	vatsa@...ibm.com, dev@...nvz.org, sekharan@...ibm.com,
	ckrm-tech@...ts.sourceforge.net, haveblue@...ibm.com,
	linux-kernel@...r.kernel.org, pj@....com, matthltc@...ibm.com,
	dipankar@...ibm.com, rohitseth@...gle.com, menage@...gle.com,
	linux-mm@...ck.org, Vaidyanathan S <svaidy@...ibm.com>
Subject: Re: [ckrm-tech] RFC: Memory Controller

Pavel Emelianov wrote:
> [snip]
> 
>>> But in general I agree, these are the three important resources for
>>> accounting and control
>> I missed out to mention, I hope you were including the page cache in
>> your definition of reclaimable memory.
> 
> As far as page cache is concerned my opinion is the following.
> (If I misunderstood you, please correct me.)
> 
> Page cache is designed to keep in memory as much pages as
> possible to optimize performance. If we start limiting the page
> cache usage we cut the performance. What is to be controlled is
> _used_ resources (touched pages, opened file descriptors, mapped
> areas, etc), but not the cached ones. I see nothing bad if the
> page that belongs to a file, but is not used by ANY task in BC,
> stays in memory. I think this is normal. If kernel wants it may
> push this page out easily it won't event need to try_to_unmap()
> it. So cached pages must not be accounted.
> 

The idea behind limiting the page cache is this

1. Lets say one container fills up the page cache.
2. The other containers will not be able to allocate memory (even
though they are within their limits) without the overhead of having
to flush the page cache and freeing up occupied cache. The kernel
will have to pageout() the dirty pages in the page cache.

Since it is easy to push the page out (as you said), it should be
easy to impose a limit on the page cache usage of a container.

> 
> I've also noticed that you've [snip]-ed on one of my questions.
> 
>  > How would you allocate memory on NUMA in advance?
> 
> Please, clarify this.

I am not quite sure I understand the question. Could you please rephrase
it and highlight some of the difficulty?

-- 

	Balbir Singh,
	Linux Technology Center,
	IBM Software Labs
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