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    SubjectRe: Kernel falls apart under light memory pressure (i.e. linking vmlinux)
    On Tue, May 24, 2011 at 7:24 AM, Andrew Lutomirski <luto@mit.edu> wrote:
    > On Mon, May 23, 2011 at 9:34 PM, Minchan Kim <minchan.kim@gmail.com> wrote:
    >> On Tue, May 24, 2011 at 10:19 AM, Andrew Lutomirski <luto@mit.edu> wrote:
    >>> On Sun, May 22, 2011 at 7:12 PM, Minchan Kim <minchan.kim@gmail.com> wrote:
    >>>> Could you test below patch based on vanilla 2.6.38.6?
    >>>> The expect result is that system hang never should happen.
    >>>> I hope this is last test about hang.
    >>>>
    >>>> Thanks.
    >>>>
    >>>> diff --git a/mm/vmscan.c b/mm/vmscan.c
    >>>> index 292582c..1663d24 100644
    >>>> --- a/mm/vmscan.c
    >>>> +++ b/mm/vmscan.c
    >>>> @@ -231,8 +231,11 @@ unsigned long shrink_slab(struct shrink_control *shrink,
    >>>>       if (scanned == 0)
    >>>>               scanned = SWAP_CLUSTER_MAX;
    >>>>
    >>>> -       if (!down_read_trylock(&shrinker_rwsem))
    >>>> -               return 1;       /* Assume we'll be able to shrink next time */
    >>>> +       if (!down_read_trylock(&shrinker_rwsem)) {
    >>>> +               /* Assume we'll be able to shrink next time */
    >>>> +               ret = 1;
    >>>> +               goto out;
    >>>> +       }
    >>>>
    >>>>       list_for_each_entry(shrinker, &shrinker_list, list) {
    >>>>               unsigned long long delta;
    >>>> @@ -286,6 +289,8 @@ unsigned long shrink_slab(struct shrink_control *shrink,
    >>>>               shrinker->nr += total_scan;
    >>>>       }
    >>>>       up_read(&shrinker_rwsem);
    >>>> +out:
    >>>> +       cond_resched();
    >>>>       return ret;
    >>>>  }
    >>>>
    >>>> @@ -2331,7 +2336,7 @@ 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;
    >>>>  }
    >>>
    >>> So far with this patch I can't reproduce the hang or the bogus OOM.
    >>>
    >>> To be completely clear, I have COMPACTION, MIGRATION, and THP off, I'm
    >>> running 2.6.38.6, and I have exactly two patches applied.  One is the
    >>> attached patch and the other is a the fpu.ko/aesni_intel.ko merger
    >>> which I need to get dracut to boot my box.
    >>>
    >>> For fun, I also upgraded to 8GB of RAM and it still works.
    >>>
    >>
    >> Hmm. Could you test it with enable thp and 2G RAM?
    >> Isn't it a original test environment?
    >> Please don't change test environment. :)
    >
    > The test that passed last night was an environment (hardware and
    > config) that I had confirmed earlier as failing without the patch.
    >
    > I just re-tested my original config (from a backup -- migration,
    > compaction, and thp "always" are enabled).  I get bogus OOMs but not a
    > hang.  (I'm running with mem=2G right now -- I'll swap the DIMMs back
    > out later on if you want.)
    >
    > I attached the bogus OOM (actually several that happened in sequence).
    >  They look readahead-related.  There was plenty of free swap space.

    Now with log actually attached.

    >
    > --Andy
    >
    [unhandled content-type:application/x-xz]
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