linux-kernel - Re: [PATCH] mm: add config option to select the initial overcommit mode

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Message-ID: <20160513095230.GI20141@dhcp22.suse.cz>
Date:	Fri, 13 May 2016 11:52:30 +0200
From:	Michal Hocko <mhocko@...nel.org>
To:	Mason <slash.tmp@...e.fr>
Cc:	Sebastian Frias <sf84@...oste.net>, linux-mm@...ck.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] mm: add config option to select the initial overcommit
 mode

On Fri 13-05-16 10:44:30, Mason wrote:
> On 13/05/2016 10:04, Michal Hocko wrote:
> 
> > On Tue 10-05-16 13:56:30, Sebastian Frias wrote:
> > [...]
> >> NOTE: I understand that the overcommit mode can be changed dynamically thru
> >> sysctl, but on embedded systems, where we know in advance that overcommit
> >> will be disabled, there's no reason to postpone such setting.
> > 
> > To be honest I am not particularly happy about yet another config
> > option. At least not without a strong reason (the one above doesn't
> > sound that way). The config space is really large already.
> > So why a later initialization matters at all? Early userspace shouldn't
> > consume too much address space to blow up later, no?
> 
> One thing I'm not quite clear on is: why was the default set
> to over-commit on?

Because many applications simply rely on large and sparsely used address
space, I guess. That's why the default is GUESS where we ignore the
cumulative charges and simply check the current state and blow up only
when the current request is way too large.
-- 
Michal Hocko
SUSE Labs