On Fri 26-08-11 11:53:56, Michal Hocko wrote:

On Fri 26-08-11 02:21:42, David Rientjes wrote:

quoted

On Fri, 26 Aug 2011, Michal Hocko wrote:

quoted

Let's give all frozen tasks a bonus (OOM_SCORE_ADJ_MAX/2) so that we do
not consider them unless really necessary and if we really pick up one
then thaw its threads before we try to kill it.

I don't like arbitrary heuristics like this because they polluted the old 
oom killer before it was rewritten and made it much more unpredictable.  
The only heuristic it includes right now is a bonus for root tasks so that 
when two processes have nearly the same amount of memory usage (within 3% 
of available memory), the non-root task is chosen instead.

This bonus is actually saying that a single frozen task can use up to 50% 
more of the machine's capacity in a system-wide oom condition than the 
task that will now be killed instead.  That seems excessive.

Yes, the number is probably too high. I just wanted to start up with
something. Maybe we can give it another root bonus. But I agree whatever
we use it will be just a random value...

quoted

I do like the idea of automatically thawing the task though and if that's 
possible then I don't think we need to manipulate the badness heuristic at 
all.  I know that wouldn't be feasible when we've frozen _all_ threads and 

Why it wouldn't be feasible for all threads? If you have all tasks
frozen (suspend going on, whole cgroup or all tasks in a cpuset/nodemask
are frozen) then the selection is more natural because all of them are
equal (with or without a bonus). The bonus tries to reduce thawing if
not all of them are frozen.
I am not saying the bonus is necessary, though. It depends on what
the freezer is used for (e.g. freeze a process which went wild and
debug what went wrong wouldn't welcome that somebody killed it or other
(mis)use which relies on D state).

Anyway, I do agree, the two things (bonus and thaw during oom_kill)
should be handled separately.

-- 
Michal Hocko
SUSE Labs
SUSE LINUX s.r.o.
Lihovarska 1060/12
190 00 Praha 9    
Czech Republic

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