linux-kernel - Re: [PATCH] oom_kill: use rss value instead of vm size for badness

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Date:	Thu, 29 Oct 2009 18:16:50 +0900
From:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To:	David Rientjes <rientjes@...gle.com>
Cc:	linux-mm@...ck.org, linux-kernel@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	Hugh Dickins <hugh.dickins@...cali.co.uk>,
	Andrea Arcangeli <aarcange@...hat.com>, vedran.furac@...il.com,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
Subject: Re: [PATCH] oom_kill: use rss value instead of vm size for badness

On Thu, 29 Oct 2009 02:01:49 -0700 (PDT)
David Rientjes <rientjes@...gle.com> wrote:
> > yes, then I wrote "as start point". There are many environments.
> 
> And this environment has a particularly bad result.
> yes, then I wrote "as start point". There are many environments.

In my understanding, 2nd, 3rd candidates are not important. If both of
total_vm and RSS catches the same process as 1st candidate, it's ok.
(i.e. If killed, oom situation will go away.)


> > ya, I'm now considering to drop file_rss from calculation.
> > 
> > some reasons.
> > 
> >   - file caches remaining in memory at OOM tend to have some trouble to remove it.
> >   - file caches tend to be shared.
> >   - if file caches are from shmem, we never be able to drop them if no swap/swapfull.
> > 
> > Maybe we'll have better result.
> > 
> 
> That sounds more appropriate.
> 
> I'm surprised you still don't see a value in using the peak VM and RSS 
> sizes, though, as part of your formula as it would indicate the proportion 
> of memory resident in RAM at the time of oom.
> 
I'll use swap_usage instead of peak VM size as bonus.

  anon_rss + swap_usage/2 ? or some.

My first purpose is not to kill not-guilty process at random.
If memory eater is killed, it's reasnoable.

In my consideration

  - "Killing a process because of OOM" is something bad, but not avoidable.

  - We don't need to do compliated/too-wise calculation for killing a process.
    "The worst one is memory-eater!" is easy to understand to users and admins.

  - We have oom_adj, now. User can customize it if he run _important_ memory eater.

  - But fork-bomb doesn't seem memory eater if we see each process.
    We need some cares.

  Then,
  - I'd like to drop file_rss.
  - I'd like to take swap_usage into acccount.
  - I'd like to remove cpu_time bonus. runtime bonus is much more important.
  - I'd like to remove penalty from children. To do that, fork-bomb detector
    is necessary.
  - nice bonus is bad. (We have oom_adj instead of this.) It should be
    if (task_nice(p) < 0)
	points /= 2;
    But we have "root user" bonus already. We can remove this line.

After above, much more simple selection, easy-to-understand,  will be done.

Thanks,
-Kame

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