linux-kernel - Re: [RFC][PATCH 1/4] Memory controller soft limit documentation

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Date:	Tue, 13 Jan 2009 17:45:54 -0800
From:	Paul Menage <menage@...gle.com>
To:	Balbir Singh <balbir@...ux.vnet.ibm.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Sudhir Kumar <skumar@...ux.vnet.ibm.com>,
	YAMAMOTO Takashi <yamamoto@...inux.co.jp>, lizf@...fujitsu.com,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	David Rientjes <rientjes@...gle.com>,
	Pavel Emelianov <xemul@...nvz.org>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Subject: Re: [RFC][PATCH 1/4] Memory controller soft limit documentation

On Wed, Jan 7, 2009 at 10:41 AM, Balbir Singh <balbir@...ux.vnet.ibm.com> wrote:
> -7. TODO
> +7. Soft limits
> +
> +Soft limits allow for greater sharing of memory. The idea behind soft limits
> +is to allow control groups to use as much of the memory as needed, provided
> +
> +a. There is no memory contention
> +b. They do not exceed their hard limit
> +
> +When the system detects memory contention (through do_try_to_free_pages(),
> +while allocating), control groups are pushed back to their soft limits if
> +possible. If the soft limit of each control group is very high, they are
> +pushed back as much as possible to make sure that one control group does not
> +starve the others.

Can you give an example here of how to implement the following setup:

- we have a high-priority latency-sensitive server job A and a bunch
of low-priority batch jobs B, C and D

- each job *may* need up to 2GB of memory, but generally each tends to
use <1GB of memory

- we want to run all four jobs on a 4GB machine

- we don't want A to ever have to wait for memory to be reclaimed (as
it's serving latency-sensitive queries), so the kernel should be
squashing B/C/D down *before* memory actually runs out.

Is this possible with the proposed hard/soft limit setup? Or do we
need some additional support for keeping a pool of pre-reserved free
memory available?

Paul
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