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

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Date:	Tue, 17 May 2016 10:24:20 +0200
From:	Sebastian Frias <sf84@...oste.net>
To:	One Thousand Gnomes <gnomes@...rguk.ukuu.org.uk>
CC:	Michal Hocko <mhocko@...nel.org>, Mason <slash.tmp@...e.fr>,
	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

Hi Alan,

On 05/13/2016 05:43 PM, One Thousand Gnomes wrote:
>> But wouldn't those affect a given process at at time?
>> Does that means that the OOM-killer is woken up to kill process X when those situations arise on process Y?
> 
> Not sure I understand the question.

I'm sorry for the "at at time" typo.
What I meant was that situations you described "Stakc expansion failure is not reportable. Copy on write failure is not reportable and so on.", should affect one process at the time, in that case:
1) either process X with the COW failure happens could die
2) either random process Y dies so that COW failure on process X can be handled.

Do you know why was 2) chosen over 1)?

> 
>> Also, under what conditions would copy-on-write fail?
> 
> When you have no memory or swap pages free and you touch a COW page that
> is currently shared. At that point there is no resource to back to the
> copy so something must die - either the process doing the copy or
> something else.

Exactly, and why does "killing something else" makes more sense (or was chosen over) "killing the process doing the copy"?

Best regards,

Sebastian