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

From: Chris Down
Date: Thu May 28 2020 - 12:41:54 EST

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.
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.