Re: Found the commit that causes the OOMs

[Wu Fengguang]

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@xxxxxxxxxx> wrote:
> 
> > Minchan Kim <minchan.kim@xxxxxxxxx> 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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