Re: Kernel falls apart under light memory pressure (i.e. linkingvmlinux)

[Wu Fengguang]

On Sun, May 15, 2011 at 12:12:36PM -0400, Andrew Lutomirski wrote:
> On Sun, May 15, 2011 at 11:27 AM, Wu Fengguang <fengguang.wu@xxxxxxxxx> wrote:
> > On Sun, May 15, 2011 at 09:37:58AM +0800, Minchan Kim wrote:
> >> On Sun, May 15, 2011 at 2:43 AM, Andi Kleen <andi@xxxxxxxxxxxxxx> wrote:
> >> > Copying back linux-mm.
> >> >
> >> >> Recently, we added following patch.
> >> >> https://lkml.org/lkml/2011/4/26/129
> >> >> If it's a culprit, the patch should solve the problem.
> >> >
> >> > It would be probably better to not do the allocations at all under
> >> > memory pressure. ÂEven if the RA allocation doesn't go into reclaim
> >>
> >> Fair enough.
> >> I think we can do it easily now.
> >> If page_cache_alloc_readahead(ie, GFP_NORETRY) is fail, we can adjust
> >> RA window size or turn off a while. The point is that we can use the
> >> fail of __do_page_cache_readahead as sign of memory pressure.
> >> Wu, What do you think?
> >
> > No, disabling readahead can hardly help.
> >
> > The sequential readahead memory consumption can be estimated by
> >
> > Â Â Â Â Â Â Â Â2 * (number of concurrent read streams) * (readahead window size)
> >
> > And you can double that when there are two level of readaheads.
> >
> > Since there are hardly any concurrent read streams in Andy's case,
> > the readahead memory consumption will be ignorable.
> >
> > Typically readahead thrashing will happen long before excessive
> > GFP_NORETRY failures, so the reasonable solutions are to
> >
> > - shrink readahead window on readahead thrashing
> > Â(current readahead heuristic can somehow do this, and I have patches
> > Âto further improve it)
> >
> > - prevent abnormal GFP_NORETRY failures
> > Â(when there are many reclaimable pages)
> >
> >
> > Andy's OOM memory dump (incorrect_oom_kill.txt.xz) shows that there are
> >
> > - 8MB Â active+inactive file pages
> > - 160MB active+inactive anon pages
> > - 1GB Â shmem pages
> > - 1.4GB unevictable pages
> >
> > Hmm, why are there so many unevictable pages? ÂHow come the shmem
> > pages become unevictable when there are plenty of swap space?
> 
> That was probably because one of my testcases creates a 1.4GB file on
> ramfs.  (I can provoke the problem without doing evil things like
> that, but the test script is rather reliable at killing my system and
> it works fine on my other machines.)

Ah I didn't read your first email.. I'm now running

./test_mempressure.sh 1500 1400 1

with mem=2G and no swap, but cannot reproduce OOM.

What's your kconfig?

> If you want, I can try to generate a trace that isn't polluted with
> the evil ramfs file.

No, thanks. However it would be valuable if you can retry with this
patch _alone_ (without the "if (need_resched()) return false;" change,
as I don't see how it helps your case).

@@ -2286,7 +2290,7 @@ static bool sleeping_prematurely(pg_data_t
*pgdat, int order, long remaining,
        * must be balanced
        */
       if (order)
-               return pgdat_balanced(pgdat, balanced, classzone_idx);
+               return !pgdat_balanced(pgdat, balanced, classzone_idx);
       else
               return !all_zones_ok;
 }

Thanks,
Fengguang
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