Date:   Mon, 5 Aug 2019 10:18:10 +0200
From:   Michal Hocko <mhocko@...nel.org>
To:     Masoud Sharbiani <msharbiani@...le.com>
Cc:     Greg KH <gregkh@...uxfoundation.org>, hannes@...xchg.org,
        vdavydov.dev@...il.com, linux-mm@...ck.org,
        cgroups@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: Possible mem cgroup bug in kernels between 4.18.0 and 5.3-rc1.

On Fri 02-08-19 16:28:25, Masoud Sharbiani wrote:
> 
> 
> > On Aug 2, 2019, at 12:14 PM, Michal Hocko <mhocko@...nel.org> wrote:
> > 
> > On Fri 02-08-19 11:00:55, Masoud Sharbiani wrote:
> >> 
> >> 
> >>> On Aug 2, 2019, at 7:41 AM, Michal Hocko <mhocko@...nel.org> wrote:
> >>> 
> >>> On Fri 02-08-19 07:18:17, Masoud Sharbiani wrote:
> >>>> 
> >>>> 
> >>>>> On Aug 2, 2019, at 12:40 AM, Michal Hocko <mhocko@...nel.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.
> 
> I was unable to use cgroups2. I’ve created the new control group, but the attempt to move a running process into it fails with ‘Device or resource busy’.

Have you enabled the memory controller for the hierarchy? Please read
Documentation/admin-guide/cgroup-v2.rst for more information.
-- 
Michal Hocko
SUSE Labs

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