Re: [RFC][PATCH] oom_kill: avoid depends on total_vm and use real RSS/swap value for oom_score (Re: Memory overcommit

[KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>]

On Tue, 27 Oct 2009 18:39:07 +0000 (GMT)
Hugh Dickins <hugh.dickins@tiscali.co.uk> wrote:

> On Tue, 27 Oct 2009, KAMEZAWA Hiroyuki wrote:
> > Now, oom-killer's score uses mm->total_vm as its base value.
> > But, in these days, applications like GUI program tend to use
> > much shared libraries and total_vm grows too high even when
> > pages are not fully mapped.
> > 
> > For example, running a program "mmap" which allocates 1 GBbytes of
> > anonymous memory, oom_score top 10 on system will be..
> > 
> >  score  PID     name
> >  89924	3938	mixer_applet2
> >  90210	3942	tomboy
> >  94753	3936	clock-applet
> >  101994	3919	pulseaudio
> >  113525	4028	gnome-terminal
> >  127340	1	init
> >  128177	3871	nautilus
> >  151003	11515	bash
> >  256944	11653	mmap <-----------------use 1G of anon
> >  425561	3829	gnome-session
> > 
> > No one believes gnome-session is more guilty than "mmap".
> > 
> > Instead of total_vm, we should use anon/file/swap usage of a process, I think.
> > This patch adds mm->swap_usage and calculate oom_score based on
> >   anon_rss + file_rss + swap_usage.
> > Considering usual applications, this will be much better information than
> > total_vm. After this patch, the score on my desktop is
> > 
> > score   PID     name
> > 4033	3176	gnome-panel
> > 4077	3113	xinit
> > 4526	3190	python
> > 4820	3161	gnome-settings-
> > 4989	3289	gnome-terminal
> > 7105	3271	tomboy
> > 8427	3177	nautilus
> > 17549	3140	gnome-session
> > 128501	3299	bash
> > 256106	3383	mmap
> > 
> > This order is not bad, I think.
> > 
> > Note: This adss new counter...then new cost is added.
> 
> I've often thought we ought to supply such a swap_usage statistic;
> and show it in /proc/pid/statsomething, presumably VmSwap in
> /proc/pid/status, even an additional field on the end of statm.
> 
Hm, ok. I'll divide this patch into

   - replace total_vm with anon_rss + file_rsss (everyone will agree this.)
   - add swap usage accounting
   - show it via /proc (may need discuss about its style.)
   - use the value at oom calculation (need discuss)

> A slight new cost, yes: doesn't matter at the swapping end, but
> would slightly impact fork and exit - I do hope we can afford it,
> because I think it should have been available all along.
> 
fork()/exit() uses batched counting. Then, we don't see overhead.


> I've not checked your patch in detail; but I do agree that basing
> OOM (physical memory) decisions on total_vm (virtual memory) has
> seemed weird, so it's well worth trying this approach.  Whether swap
> should be included along with rss isn't quite clear to me: I'm not
> saying you're wrong, not at all, just that it's not quite obvious.
> 
yes. It just comes from heuristics. It will need discuss/investigation/theory.


> I've several observations to make about bad OOM kill decisions,
> but it's probably better that I make them in the original
> "Memory overcommit" thread, rather than divert this thread.
> 

Thanks,
-Kame


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