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

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Message-ID: <CAF-E8XFQFm9GrBnkax+TiByUPHxp=Ukp1LcuAWjYL0OeLE1Saw@mail.gmail.com>
Date:	Fri, 5 Apr 2013 09:02:29 -0600
From:	Andrew Shewmaker <agshew@...il.com>
To:	Simon Jeons <simon.jeons@...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

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.

> 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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