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SubjectRe: Possible mem cgroup bug in kernels between 4.18.0 and 5.3-rc1.
On Fri 02-08-19 11:00:55, Masoud Sharbiani wrote:
>
>
> > On Aug 2, 2019, at 7:41 AM, Michal Hocko <mhocko@kernel.org> wrote:
> >
> > On Fri 02-08-19 07:18:17, Masoud Sharbiani wrote:
> >>
> >>
> >>> On Aug 2, 2019, at 12:40 AM, Michal Hocko <mhocko@kernel.org> wrote:
> >>>
> >>> On Thu 01-08-19 11:04:14, Masoud Sharbiani wrote:
> >>>> Hey folks,
> >>>> I’ve come across an issue that affects most of 4.19, 4.20 and 5.2 linux-stable kernels that has only been fixed in 5.3-rc1.
> >>>> It was introduced by
> >>>>
> >>>> 29ef680 memcg, oom: move out_of_memory back to the charge path
> >>>
> >>> This commit shouldn't really change the OOM behavior for your particular
> >>> test case. It would have changed MAP_POPULATE behavior but your usage is
> >>> triggering the standard page fault path. The only difference with
> >>> 29ef680 is that the OOM killer is invoked during the charge path rather
> >>> than on the way out of the page fault.
> >>>
> >>> Anyway, I tried to run your test case in a loop and leaker always ends
> >>> up being killed as expected with 5.2. See the below oom report. There
> >>> must be something else going on. How much swap do you have on your
> >>> system?
> >>
> >> I do not have swap defined.
> >
> > OK, I have retested with swap disabled and again everything seems to be
> > working as expected. The oom happens earlier because I do not have to
> > wait for the swap to get full.
> >
>
> In my tests (with the script provided), it only loops 11 iterations before hanging, and uttering the soft lockup message.
>
>
> > Which fs do you use to write the file that you mmap?
>
> /dev/sda3 on / type xfs (rw,relatime,seclabel,attr2,inode64,logbufs=8,logbsize=32k,noquota)
>
> Part of the soft lockup path actually specifies that it is going through __xfs_filemap_fault():

Right, I have just missed that.

[...]

> If I switch the backing file to a ext4 filesystem (separate hard drive), it OOMs.
>
>
> If I switch the file used to /dev/zero, it OOMs:
> …
> Todal sum was 0. Loop count is 11
> Buffer is @ 0x7f2b66c00000
> ./test-script-devzero.sh: line 16: 3561 Killed ./leaker -p 10240 -c 100000
>
>
> > Or could you try to
> > simplify your test even further? E.g. does everything work as expected
> > when doing anonymous mmap rather than file backed one?
>
> It also OOMs with MAP_ANON.
>
> Hope that helps.

It helps to focus more on the xfs reclaim path. Just to be sure, is
there any difference if you use cgroup v2? I do not expect to be but
just to be sure there are no v1 artifacts.
--
Michal Hocko
SUSE Labs

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