linux-kernel - Re: [PATCH v7 2/2] mm: replace hardcoded 3% with admin_reserve

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Date:	Sun, 07 Apr 2013 08:48:04 +0800
From:	Simon Jeons <simon.jeons@...il.com>
To:	Andrew Shewmaker <agshew@...il.com>
CC:	Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org, alan@...rguk.ukuu.org.uk,
	ric.masonn@...il.com
Subject: Re: [PATCH v7 2/2] mm: replace hardcoded 3% with admin_reserve_pages
 knob

Hi Andrew,
On 04/05/2013 11:02 PM, Andrew Shewmaker wrote:
> On Wed, Apr 3, 2013 at 9:50 PM, Simon Jeons <simon.jeons@...il.com> wrote:
>>> FAQ
>>>
> ...
>>>    * How do you calculate a minimum useful reserve?
>>>
>>>      A user or the admin needs enough memory to login and perform
>>>      recovery operations, which includes, at a minimum:
>>>
>>>      sshd or login + bash (or some other shell) + top (or ps, kill, etc.)
>>>
>>>      For overcommit 'guess', we can sum resident set sizes (RSS).
>>>      On x86_64 this is about 8MB.
>>>
>>>      For overcommit 'never', we can take the max of their virtual sizes
>>> (VSZ)
>>>      and add the sum of their RSS.
>>>      On x86_64 this is about 128MB.
>>
>> 1.Why has this different between guess and never?
> The default, overcommit 'guess' mode, only needs a reserve for
> what the recovery programs will typically use. Overcommit 'never'
> mode will only successfully launch an app when it can fulfill all of
> its requested memory allocations--even if the app only uses a
> fraction of what it asks for.

VSZ has already cover RSS, is it? why account RSS again?

>
>> 2.You just test x86/x86_64, other platforms also will use memory overcommit,
>> did you test them?
> No, I haven't. Unfortunately, I don't currently have any other platforms to test
> with. I'll see what I can do.
>
> Thanks,
>
> Andrew

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