linux-kernel - Re: [patch] mm: oom_kill: revert 3% system memory bonus for privileged tasks

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Message-ID: <alpine.DEB.2.02.1401212050340.8512@chino.kir.corp.google.com>
Date:	Tue, 21 Jan 2014 20:53:07 -0800 (PST)
From:	David Rientjes <rientjes@...gle.com>
To:	Johannes Weiner <hannes@...xchg.org>
cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Michal Hocko <mhocko@...e.cz>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: [patch] mm: oom_kill: revert 3% system memory bonus for privileged
 tasks

On Thu, 16 Jan 2014, Johannes Weiner wrote:

> > Unfortunately, I think this could potentially be too much of a bonus.  On 
> > your same 32GB machine, if a root process is using 18GB and a user process 
> > is using 14GB, the user process ends up getting selected while the current 
> > discount of 3% still selects the root process.
> > 
> > I do like the idea of scaling this bonus depending on points, however.  I 
> > think it would be better if we could scale the discount but also limit it 
> > to some sane value.
> 
> I just reverted to the /= 4 because we had that for a long time and it
> seemed to work.  I don't really mind either way as long as we get rid
> of that -3%.  Do you have a suggestion?
> 

How about simply using 3% of the root process's points so that root 
processes get some bonus compared to non-root processes with the same 
memory usage and it's scaled to the usage rather than amount of available 
memory?

So rather than points /= 4, we do

	if (has_capability_noaudit(p, CAP_SYS_ADMIN))
		points -= (points * 3) / 100;

instead.  Sound good?
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