On Tue, Sep 08, 2020 at 11:50:51AM -0700, Julius Hemanth Pitti wrote: > For non root CG, in try_charge(), we keep trying > to charge until we succeed. On non-preemptive > kernel, when we are OOM, this results in holding > CPU forever. > > On SMP systems, this doesn't create a big problem > because oom_reaper get a change to kill victim > and make some free pages. However on a single-core > CPU (or cases where oom_reaper pinned to same CPU > where try_charge is executing), oom_reaper shall > never get scheduled and we stay in try_charge forever. > > Steps to repo this on non-smp: > 1. mount -t tmpfs none /sys/fs/cgroup > 2. mkdir /sys/fs/cgroup/memory > 3. mount -t cgroup none /sys/fs/cgroup/memory -o memory > 4. mkdir /sys/fs/cgroup/memory/0 > 5. echo 40M > /sys/fs/cgroup/memory/0/memory.limit_in_bytes > 6. echo $$ > /sys/fs/cgroup/memory/0/tasks > 7. stress -m 5 --vm-bytes 10M --vm-hang 0 > > Signed-off-by: Julius Hemanth Pitti <jpitti@xxxxxxxxx> > --- > mm/memcontrol.c | 2 ++ > 1 file changed, 2 insertions(+) > > diff --git a/mm/memcontrol.c b/mm/memcontrol.c > index 0d6f3ea86738..4620d70267cb 100644 > --- a/mm/memcontrol.c > +++ b/mm/memcontrol.c > @@ -2652,6 +2652,8 @@ static int try_charge(struct mem_cgroup *memcg, gfp_t gfp_mask, > if (fatal_signal_pending(current)) > goto force; > > + cond_resched(); > + Can you, please, add a short comment here? Something like "give oom_reaper a chance on a non-SMP system"? > /* > * keep retrying as long as the memcg oom killer is able to make > * a forward progress or bypass the charge if the oom killer > -- > 2.17.1 > The patch makes total sense to me. Please, feel free to add Acked-by: Roman Gushchin <guro@xxxxxx> after adding a comment. Thank you!
