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

[KAMEZAWA Hiroyuki]

On Thu, 29 Oct 2009 01:31:59 -0700 (PDT)
David Rientjes <rientjes@xxxxxxxxxx> wrote:

> On Thu, 29 Oct 2009, KAMEZAWA Hiroyuki wrote:
> 
> > From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx>
> > 
> > It's reported that OOM-Killer kills Gnone/KDE at first...
> > And yes, we can reproduce it easily.
> > 
> > Now, oom-killer uses mm->total_vm as its base value. But in recent
> > applications, there are a big gap between VM size and RSS size.
> > Because
> >   - Applications attaches much dynamic libraries. (Gnome, KDE, etc...)
> >   - Applications may alloc big VM area but use small part of them.
> >     (Java, and multi-threaded applications has this tendency because
> >      of default-size of stack.)
> > 
> > I think using mm->total_vm as score for oom-kill is not good.
> > By the same reason, overcommit memory can't work as expected.
> > (In other words, if we depends on total_vm, using overcommit more positive
> >  is a good choice.)
> > 
> > This patch uses mm->anon_rss/file_rss as base value for calculating badness.
> > 
> > Following is changes to OOM score(badness) on an environment with 1.6G memory
> > plus memory-eater(500M & 1G).
> > 
> > Top 10 of badness score. (The highest one is the first candidate to be killed)
> > Before
> > badness program
> > 91228	gnome-settings-
> > 94210	clock-applet
> > 103202	mixer_applet2
> > 106563	tomboy
> > 112947	gnome-terminal
> > 128944	mmap              <----------- 500M malloc
> > 129332	nautilus
> > 215476	bash              <----------- parent of 2 mallocs.
> > 256944	mmap              <----------- 1G malloc
> > 423586	gnome-session
> > 
> > After
> > badness 
> > 1911	mixer_applet2
> > 1955	clock-applet
> > 1986	xinit
> > 1989	gnome-session
> > 2293	nautilus
> > 2955	gnome-terminal
> > 4113	tomboy
> > 104163	mmap             <----------- 500M malloc.
> > 168577	bash             <----------- parent of 2 mallocs
> > 232375	mmap             <----------- 1G malloc
> > 
> > seems good for me. Maybe we can tweak this patch more,
> > but this one will be a good one as a start point.
> > 
> 
> This appears to actually prefer X more than total_vm in Vedran's test 
> case.  He cited http://pastebin.com/f3f9674a0 in 
> http://marc.info/?l=linux-kernel&m=125678557002888.
> 
> There are 12 ooms in this log, which has /proc/sys/vm/oom_dump_tasks 
> enabled.  It shows the difference between the top total_vm candidates vs. 
> the top rss candidates.
> 
> total_vm
> 708945 test
> 195695 krunner
> 168881 plasma-desktop
> 130567 ktorrent
> 127081 knotify4
> 125881 icedove-bin
> 123036 akregator
> 118641 kded4
> 
> rss
> 707878 test
> 42201 Xorg
> 13300 icedove-bin
> 10209 ktorrent
> 9277 akregator
> 8878 plasma-desktop
> 7546 krunner
> 4532 mysqld
> 
> This patch would pick the memory hogging task, "test", first everytime 
> just like the current implementation does.  It would then prefer Xorg, 
> icedove-bin, and ktorrent next as a starting point.
> 
> Admittedly, there are other heuristics that the oom killer uses to create 
> a badness score.  But since this patch is only changing the baseline from 
> mm->total_vm to get_mm_rss(mm), its behavior in this test case do not 
> match the patch description.
> 
yes, then I wrote "as start point". There are many environments.
But I'm not sure why ntpd can be the first candidate...
The scores you shown doesn't include children's score, right ?

I believe I'll have to remove "adding child's score to parents".
I'm now considering how to implement fork-bomb detector for removing it.

> The vast majority of the other ooms have identical top 8 candidates:
> 
> total_vm
> 673222 test
> 195695 krunner
> 168881 plasma-desktop
> 130567 ktorrent
> 127081 knotify4
> 125881 icedove-bin
> 123036 akregator
> 121869 firefox-bin
> 
> rss
> 672271 test
> 42192 Xorg
> 30763 firefox-bin
> 13292 icedove-bin
> 10208 ktorrent
> 9260 akregator
> 8859 plasma-desktop
> 7528 krunner
> 
> firefox-bin seems much more preferred in this case than total_vm, but Xorg 
> still ranks very high with this patch compared to the current 
> implementation.
> 
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.

Regards,
-Kame




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