linux-kernel - Re: [PATCH 2/2 v2] mm: allow to set overcommit ratio more precisely

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Message-ID: <5229949C.6090904@redhat.com>
Date:	Fri, 06 Sep 2013 10:38:52 +0200
From:	Jerome Marchand <jmarchan@...hat.com>
To:	Pavel Machek <pavel@....cz>
CC:	Dave Hansen <dave.hansen@...el.com>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2 v2] mm: allow to set overcommit ratio more precisely

On 09/06/2013 12:11 AM, Pavel Machek wrote:
> hi!
> 
>>>> 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.
>>>
>>> Looks like a pretty sane solution.  Could you also make a Documentation/
>>> update, please?
>>
>> Damn! I forgot. Will do.
> 
> Actually... would something like overcommit_bytes be better interface? overcommit_pages?
> 
> If system would normally allow allocating "n" pages, with overcommit
> it would allow allocating "n + overcommit_pages" pages. That seems
> like right granularity...
> 

I don't know what do you mean by "normally".
Anyway, I've considered that option: my concern about mixing absolute and
proportional values is that they would diverge if the amount of ram varies
(e.g. memory hotplug or virt baloon driver).
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