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SubjectRe: Found the commit that causes the OOMs
On Thu, Jul 02, 2009 at 03:41:06PM +0800, Minchan Kim wrote:
>
>
> On Tue, 30 Jun 2009 20:57:47 +0100
> David Howells <dhowells@redhat.com> wrote:
>
> > Minchan Kim <minchan.kim@gmail.com> wrote:
> >
> > > David. Doesn't it happen OOM if you revert my patch, still?
> >
> > It does happen, and indeed happens in v2.6.30, but requires two adjacent runs
> > of msgctl11 to trigger, rather than usually triggering on the first run. If
> > you interpolate the rest of LTP between the iterations, it doesn't seem to
> > happen at all on v2.6.30. My guess is that with the rest of LTP interpolated,
> > there's either enough time for some cleanup or something triggers a cleanup
> > (the swapfile tests perhaps?).
> >
> > > Befor I go to the trip, I made debugging patch in a hurry. Mel and I
> > > suspect to put the wrong page in lru list.
> > >
> > > This patch's goal is that print page's detail on active anon lru when it
> > > happen OOM. Maybe you could expand your log buffer size.
> >
> > Do you mean to expand the dmesg buffer? That's probably unnecessary: I capture
> > the kernel log over a serial port into a file on another machine.
> >
> > > Could you show me the information with OOM, please ?
> >
> > Attached. It's compressed as there was rather a lot.
> >
> > David
> > ---
>
> Hi, David.
>
> Sorry for late response.
>
> I looked over your captured data when I got home but I didn't find any problem
> in lru page moving scheme.
> As Wu, Kosaki and Rik discussed, I think this issue is also related to process fork bomb.

Yes, me think so.

> When I tested msgctl11 in my machine with 2.6.31-rc1, I found that:

Were you testing the no-swap case?

> 2.6.31-rc1
> real 0m38.628s
> user 0m10.589s
> sys 1m12.613s
>
> vmstat
>
> allocstall 3196
>
> 2.6.31-rc1-revert-mypatch
>
> real 1m17.396s
> user 0m11.193s
> sys 4m3.803s

It's interesting that (sys > real).
> vmstat
>
> allocstall 584
>
> Sometimes I got OOM, sometime not in with 2.6.31-rc1.
>
> Anyway, the current kernel's test took a rather short time than my reverted patch.
> In addition, the current kernel has small allocstall(direct reclaim)
>
> As you know, my patch was just to remove calling shrink_active_list in case of no swap.
> shrink_active_list function is a big cost function.
> The old shrink_active_list could throttle to fork processes by chance.
> But by removing that function with my patch, we have a high
> probability to make process fork bomb. Wu, KOSAKI and Rik, does it
> make sense?

Maybe, but I'm not sure on how to explain the time/vmstat numbers :(

> So I think you were just lucky with a unnecessary routine.
> Anyway, AFAIK, Rik is making throttling page reclaim.
> I think it can solve your problem.

Yes, with good luck :)

Thanks,
Fengguang


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