Re: mm: mkfs.ext4 invoked oom-killer on i386 - pagecache_get_page

[Chris Down]

Naresh Kamboju writes:
> On Thu, 28 May 2020 at 20:33, Michal Hocko <mhocko@xxxxxxxxxx> wrote:
> > On Fri 22-05-20 02:23:09, Naresh Kamboju wrote:
> > > My apology !
> > > As per the test results history this problem started happening from
> > > Bad : next-20200430 (still reproducible on next-20200519)
> > > Good : next-20200429
> > >
> > > The git tree / tag used for testing is from linux next-20200430 tag and reverted
> > > following three patches and oom-killer problem fixed.
> > >
> > > Revert "mm, memcg: avoid stale protection values when cgroup is above
> > > protection"
> > > Revert "mm, memcg: decouple e{low,min} state mutations from protectinn checks"
> > > Revert "mm-memcg-decouple-elowmin-state-mutations-from-protection-checks-fix"
> >
> > The discussion has fragmented and I got lost TBH.
> > In http://lkml.kernel.org/r/CA+G9fYuDWGZx50UpD+WcsDeHX9vi3hpksvBAWbMgRZadb0Pkww@xxxxxxxxxxxxxx
> > you have said that none of the added tracing output has triggered. Does
> > this still hold? Because I still have a hard time to understand how
> > those three patches could have the observed effects.
>
> On the other email thread [1] this issue is concluded.
>
> Yafang wrote on May 22 2020,
>
> Regarding the root cause, my guess is it makes a similar mistake that
> I tried to fix in the previous patch that the direct reclaimer read a
> stale protection value.  But I don't think it is worth to add another
> fix. The best way is to revert this commit.

This isn't a conclusion, just a guess (and one I think is unlikely). For this 
to reliably happen, it implies that the same race happens the same way each 
time.