linux-kernel - Re: [PATCH] Repeated fork() causes SLAB to grow without bound

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Date:	Tue, 18 Nov 2014 21:48:00 -0500
From:	Rik van Riel <riel@...hat.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
CC:	Michel Lespinasse <walken@...gle.com>,
	Hugh Dickins <hughd@...gle.com>,
	Andrea Arcangeli <aarcange@...hat.com>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	Tim Hartrick <tim@...ecast.com>, Michal Hocko <mhocko@...e.cz>
Subject: Re: [PATCH] Repeated fork() causes SLAB to grow without bound

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On 11/18/2014 03:19 PM, Andrew Morton wrote:
> On Mon, 17 Nov 2014 21:41:57 -0500 Rik van Riel <riel@...hat.com>
> wrote:
> 

>> That way people can understand what the code does simply by
>> looking at the changelog - no need to go find old linux-kernel
>> mailing list threads.
> 
> Yes please, there's a ton of stuff here which we should attempt to 
> capture.
> 
> https://lkml.org/lkml/2012/8/15/765 is useful.
> 
> I'm assuming that with the "foo < 5" hack, an application which
> forked 5 times then did a lot of work would still trigger the
> "catastrophic issue at page reclaim time" issue which Rik
> identified at https://lkml.org/lkml/2012/8/20/265?

It's not "forking 5 times", it is "forking >>5 generations deep".

There are a few programs that do that, but it does not appear
that they are forking servers like apache or sendmail (which
fork from the 2nd generation, and then sometimes again to exec
a helper from the 4th generation).

> There are real-world workloads which are triggering this slab
> growth problem, yes?  (Detail them in the changelog, please).

There are, but the overlap between "forks >>5 generations deep"
and "forks a bajillion child processes" appears to be zero.

- -- 
All rights reversed
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