linux-kernel - Re: [PATCH 2/2] mm: add overcommit

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Date:	Mon, 19 Aug 2013 09:55:03 -0700
From:	Dave Hansen <dave.hansen@...el.com>
To:	Jerome Marchand <jmarchan@...hat.com>
CC:	linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] mm: add overcommit_kbytes sysctl variable

On 08/19/2013 08:17 AM, Jerome Marchand 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_kbytes sysctl variable that allow a
> much finer grain.

Instead of introducing yet another tunable, why don't we just make the
ratio that comes in from the user more fine-grained?

	sysctl overcommit_ratio=0.2

We change the internal 'sysctl_overcommit_ratio' to store tenths or
hundreths of a percent (or whatever), then parse the input as two
integers.  I don't think we need fully correct floating point parsing
and rounding here, so it shouldn't be too much of a chore.  It'd
probably end up being less code than you have as it stands.
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