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

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Message-ID: <6599ad830610310922p61913cdaqb441a2cb718420a9@mail.gmail.com>
Date:	Tue, 31 Oct 2006 09:22:25 -0800
From:	"Paul Menage" <menage@...gle.com>
To:	balbir@...ibm.com
Cc:	dev@...nvz.org, vatsa@...ibm.com, 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
Subject: Re: [ckrm-tech] RFC: Memory Controller

On 10/31/06, Balbir Singh <balbir@...ibm.com> wrote:
>
> I am still a little concerned about how limit size changes will be implemented.
> Will the cpuset "mems" field change to reflect the changed limits?

That's how we've been doing it - increasing limits is easy, shrinking
them is harder ...

> > Page cache control is actually more essential that RSS control, in our
> > experience - it's pretty easy to track RSS values from userspace, and
> > react reasonably quickly to kill things that go over their limit, but
> > determining page cache usage (i.e. determining which job on the system
> > is flooding the page cache with dirty buffers) is pretty much
> > impossible currently.
> >
>
> Hmm... interesting. Why do you think its impossible, what are the kinds of
> issues you've run into?
>

Issues such as:

- determining from userspace how much of the page cache is really
"free" memory that can be given out to new jobs without impacting the
performance of existing jobs

- determining which job on the system is flooding the page cache with
dirty buffers

- accounting the active pagecache usage of a job as part of its memory
footprint (if a process is only 1MB large but is seeking randomly
through a 1GB file, treating it as only using/needing 1MB isn't
practical).

Paul
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