linux-kernel - Re: [PATCH v4 2/2] mm: allow to set overcommit ratio more precisely

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Message-Id: <20131105155319.732dcbefb162c2ee4716ef9d@linux-foundation.org>
Date:	Tue, 5 Nov 2013 15:53:19 -0800
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Jerome Marchand <jmarchan@...hat.com>
Cc:	linux-mm@...ck.org, linux-kernel@...r.kernel.org,
	dave.hansen@...el.com
Subject: Re: [PATCH v4 2/2] mm: allow to set overcommit ratio more precisely

On Fri, 18 Oct 2013 14:56:59 +0200 Jerome Marchand <jmarchan@...hat.com> wrote:

> Some applications that run on HPC clusters are designed around the
> availability of RAM and the overcommit ratio is fine tuned to get the
> maximum usage of memory without swapping. With growing memory, the 1%
> of all RAM grain provided by overcommit_ratio has become too coarse
> for these workload (on a 2TB machine it represents no less than
> 20GB).
> 
> This patch adds the new overcommit_ratio_ppm sysctl variable that
> allow to set overcommit ratio with a part per million precision.
> The old overcommit_ratio variable can still be used to set and read
> the ratio with a 1% precision. That way, overcommit_ratio interface
> isn't broken in any way that I can imagine.

The way we've permanently squished this mistake in the past is to
switch to "bytes".  See /proc/sys/vm/*bytes.

Would that approach work in this case?
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