linux-kernel - Re: additional oom-killer tuneable worth submitting?

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Message-ID: <9a8748490612071050q60b378c4ldf039140ffd721be@mail.gmail.com>
Date:	Thu, 7 Dec 2006 19:50:49 +0100
From:	"Jesper Juhl" <jesper.juhl@...il.com>
To:	"Chris Friesen" <cfriesen@...tel.com>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: additional oom-killer tuneable worth submitting?

A few questions below.

On 07/12/06, Chris Friesen <cfriesen@...tel.com> wrote:
>
> The kernel currently has a way to adjust the oom-killer score via
> /proc/<pid>/oomadj.
>
> However, to adjust this effectively requires knowledge of the scores of
> all the other processes on the system.
>
> I'd like to float an idea (which we've implemented and been using for
> some time) where the semantics are slightly different:
>
> We add a new "oom_thresh" member to the task struct.
> We introduce a new proc entry "/proc/<pid>/oomthresh" to control it.
>

How does "oomthresh" and "oomadj" affect each other?

> The "oom-thresh" value maps to the max expected memory consumption for
> that process.  As long as a process uses less memory than the specified
> threshold, then it is immune to the oom-killer.
>

Default "oomthresh" value for a new process is 0 (zero) I assume -
right?  If not, then I'd suggest that it should be.

What happens when a process fork()s? Does the child enherit the
parents "oomthresh" value?

Would it make sense to make "oomthresh" apply to process groups
instead of processes?

> On an embedded platform this allows the designer to engineer the system
> and protect critical apps based on their expected memory consumption.
> If one of those apps goes crazy and starts chewing additional memory
> then it becomes vulnerable to the oom killer while the other apps remain
> protected.
>

What happens in the case where the OOM killer really, really needs to
kill one or more processes since there is not a single drop of memory
available, but all processes are below their configured thresholds?

> If a patch for the above feature was submitted, would there be any
> chance of getting it included?  Maybe controlled by a config option?

Impossible to know without posting the patch for review :)

-- 
Jesper Juhl <jesper.juhl@...il.com>
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