Re: Found the commit that causes the OOMs

[KOSAKI Motohiro]

> >> OK. thanks.
> >> I plan to submit this patch after small more tests. it is useful for OOM analysis.
> >
> > It is also useful for throttling page reclaim.
> >
> > If more than half of the inactive pages in a zone are
> > isolated, we are probably beyond the point where adding
> > additional reclaim processes will do more harm than good.
> 
> Maybe we can try limiting the isolation phase of direct reclaims to
> one per CPU?
> 
>         mutex_lock(per_cpu_lock);
>         isolate_pages();
>         shrink_page_list();
>         put_back_pages();
>         mutex_unlock(per_cpu_lock);
> 
> This way the isolated pages as well as major parts of direct reclaims
> will be bounded by CPU numbers. The added overheads should be trivial
> comparing to the reclaim costs.

hm, this idea makes performance degression on few CPU machine, I think.

e.g.
if system have only one cpu and sysmtem makes lumpy reclaim, lumpy reclaim
makes synchronous pageout and it makes very long waiting time.

I suspect per-cpu decision is not useful in this area.

thanks.


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