On 9/3/19 10:41 AM, Michal Hocko wrote: > On Mon 02-09-19 21:34:29, Thomas Lindroth wrote: >> On 9/2/19 9:16 AM, Michal Hocko wrote: >>> On Sun 01-09-19 22:43:05, Thomas Lindroth wrote: >>>> After upgrading to the 4.19 series I've started getting problems with >>>> early OOM. >>> >>> What is the kenrel you have updated from? Would it be possible to try >>> the current Linus' tree? >> >> I did some more testing and it turns out this is not a regression after all. >> >> I followed up on my hunch and monitored memory.kmem.max_usage_in_bytes while >> running cgexec -g memory:12G bash -c 'find / -xdev -type f -print0 | \ >> xargs -0 -n 1 -P 8 stat > /dev/null' >> >> Just as memory.kmem.max_usage_in_bytes = memory.kmem.limit_in_bytes the OOM >> killer kicked in and killed my X server. >> >> Using the find|stat approach it was easy to test the problem in a testing VM. >> I was able to reproduce the problem in all these kernels: >> 4.9.0 >> 4.14.0 >> 4.14.115 >> 4.19.0 >> 5.2.11 >> >> 5.3-rc6 didn't build in the VM. The build environment is too old probably. >> >> I was curious why I initially couldn't reproduce the problem in 4.14 by >> building chromium. I was again able to successfully build chromium using >> 4.14.115. Turns out memory.kmem.max_usage_in_bytes was 1015689216 after >> building and my limit is set to 1073741824. I guess some unrelated change in >> memory management raised that slightly for 4.19 triggering the problem. >> >> If you want to reproduce for yourself here are the steps: >> 1. build any kernel above 4.9 using something like my .config >> 2. setup a v1 memory cgroup with memory.kmem.limit_in_bytes lower than >> memory.limit_in_bytes. I used 100M in my testing VM. >> 3. Run "find / -xdev -type f -print0 | xargs -0 -n 1 -P 8 stat > /dev/null" >> in the cgroup. >> 4. Assuming there is enough inodes on the rootfs the global OOM killer >> should kick in when memory.kmem.max_usage_in_bytes = >> memory.kmem.limit_in_bytes and kill something outside the cgroup. > > This is certainly a bug. Is this still an OOM triggered from > pagefault_out_of_memory? Since 4.19 (29ef680ae7c21) the memcg charge > path should invoke the memcg oom killer directly from the charge path. > If that doesn't happen then the failing charge is either GFP_NOFS or a > large allocation. > > The former has been fixed just recently by http://lkml.kernel.org/r/cbe54ed1-b6ba-a056-8899-2dc42526371d@xxxxxxxxxxxxxxxxxxx > and I suspect this is a fix you are looking for. Although it is curious > that you can see a global oom even before because the charge path would > mark an oom situation even for NOFS context and it should trigger the > memcg oom killer on the way out from the page fault path. So essentially > the same call trace except the oom killer should be constrained to the > memcg context. > > Could you try the above patch please? > It won't help. We hitting ->kmem limit here, not the ->memory or ->memsw, so try_charge() is successful and only __memcg_kmem_charge_memcg() fails to charge ->kmem and returns -ENOMEM. Limiting kmem just never worked and it doesn't work now. AFAIK this feature hasn't been finished because there was no clear purpose/use case found. I remember that there was some discussion on lsfmm about this https://lwn.net/Articles/636331/ but I don't remember the discussion itself.
