linux-kernel - Re: [PATCH, RFC] mm: Implement RLIMIT

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Date:	Tue, 11 Jun 2013 17:53:20 -0400
From:	Jörn Engel <joern@...fs.org>
To:	Johannes Weiner <hannes@...xchg.org>
Cc:	linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH, RFC] mm: Implement RLIMIT_RSS

On Tue, 11 June 2013 17:16:01 -0400, Johannes Weiner wrote:
> On Tue, Jun 11, 2013 at 02:29:21PM -0400, Jörn Engel wrote:
> > I've seen a couple of instances where people try to impose a vsize
> > limit simply because there is no rss limit in Linux.  The vsize limit
> > is a horrible approximation and even this patch seems to be an
> > improvement.
> > 
> > Would there be strong opposition to actually supporting RLIMIT_RSS?
> 
> This is trivial to exploit by creating the mappings first and
> populating them later, so while it may cover some use cases, it does
> not have the protection against malicious programs aspect that all the
> other rlimits have.

Hm.  The use case I have is that an application wants to limit itself.
It is effectively a special assert to catch memory leaks and the like.
So malicious programs are not my immediate concern.

Of course the moment Linux supports RLIMIT_RSS people will use it to
limit malicious programs, no matter how many scary warning we put in.

> The right place to enforce the limit is at the point of memory
> allocation, which raises the question what to do when the limit is
> exceeded in a page fault.  Reclaim from the process's memory?  Kill
> it?
> 
> I guess the answer to these questions is "memory cgroups", so that's
> why there is no real motivation to implement RLIMIT_RSS separately...

Lack of opposition would be enough for me.  But I guess we need a bit
more for a mergeable patch than I did and I only did the existing
patch because it seemed easy, not because it is important.  Will keep
the patch in my junk code folder for now.

Jörn

--
A surrounded army must be given a way out.
-- Sun Tzu
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