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SubjectRe: [RFC] oom-kill: give the dying task a higher priority
On Fri, May 28, 2010 at 11:36:17AM -0300, Luis Claudio R. Goncalves wrote:
> On Fri, May 28, 2010 at 11:06:23PM +0900, Minchan Kim wrote:
> | On Fri, May 28, 2010 at 09:53:05AM -0300, Luis Claudio R. Goncalves wrote:
> | > On Fri, May 28, 2010 at 02:59:02PM +0900, KOSAKI Motohiro wrote:
> ...
> | > | As far as my observation, RT-function always have some syscall. because pure
> | > | calculation doesn't need deterministic guarantee. But _if_ you are really
> | > | using such priority design. I'm ok maximum NonRT priority instead maximum
> | > | RT priority too.
> | >
> | > I confess I failed to distinguish memcg OOM and system OOM and used "in
> | > case of OOM kill the selected task the faster you can" as the guideline.
> | > If the exit code path is short that shouldn't be a problem.
> | >
> | > Maybe the right way to go would be giving the dying task the biggest
> | > priority inside that memcg to be sure that it will be the next process from
> | > that memcg to be scheduled. Would that be reasonable?
> |
> | Hmm. I can't understand your point.
> | What do you mean failing distinguish memcg and system OOM?
> |
> | We already have been distinguish it by mem_cgroup_out_of_memory.
> | (but we have to enable CONFIG_CGROUP_MEM_RES_CTLR).
> | So task selected in select_bad_process is one out of memcg's tasks when
> | memcg have a memory pressure.
>
> The approach of giving the highest priority to the dying task makes sense
> in a system wide OOM situation. I though that would also be good for the
> memcg OOM case.
>
> After Balbir Singh's comment, I understand that in a memcg OOM the dying
> task should have a priority just above the priority of the main task of
> that memcg, in order to avoid interfering in the rest of the system.
>
> That is the point where I failed to distinguish between memcg and system OOM.
>
> Should I pursue that new idea of looking for the right priority inside the
> memcg or is it overkill? I really don't have a clear view of the impact of
> a memcg OOM on system performance - don't know if it is better to solve the
> issue sooner (highest RT priority) or leave it to be solved later (highest
> prio on the memcg). I have the impression the general case points to the
> simpler solution.

I think highest RT proirity ins't good solution.
As I mentiond, Some RT functions don't want to be preempted by other processes
which cause memory pressure. It makes RT task broken.

On the other hand, normal processes don't have a requirement of RT.
But it isn't a big problem that it lost little time slice, I think.
So how about raising max normal priority?
but I am not sure this is right solution.
Let's listen other's opinion.
I believe Peter have a good idea.

>
> Luis
> --
> [ Luis Claudio R. Goncalves Bass - Gospel - RT ]
> [ Fingerprint: 4FDD B8C4 3C59 34BD 8BE9 2696 7203 D980 A448 C8F8 ]
>

--
Kind regards,
Minchan Kim


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