On Tue, 2020-09-08 at 13:31 -0700, Yang Shi wrote:
> On Tue, Sep 8, 2020 at 1:14 PM Julius Hemanth Pitti <jpitti@xxxxxxxxx
> > 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
>
> Isn't it the same problem solved by e3336cab2579 ("mm: memcg: fix
> memcg reclaim soft lockup")? It has been in Linus's tree.
Yes, indeed.
I just tested with e3336cab2579, and it solved this problem.
Thanks for pointing it out.
>
> >
> > Signed-off-by: Julius Hemanth Pitti <jpitti@xxxxxxxxx>
> > Acked-by: Roman Gushchin <guro@xxxxxx>
> > ---
> >
> > Changes in v2:
> > - Added comments.
> > - Added "Acked-by: Roman Gushchin <guro@xxxxxx>".
> > ---
> > mm/memcontrol.c | 9 +++++++++
> > 1 file changed, 9 insertions(+)
> >
> > diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> > index cfa6cbad21d5..4f293bf8c7ed 100644
> > --- a/mm/memcontrol.c
> > +++ b/mm/memcontrol.c
> > @@ -2745,6 +2745,15 @@ static int try_charge(struct mem_cgroup
> > *memcg, gfp_t gfp_mask,
> > if (fatal_signal_pending(current))
> > goto force;
> >
> > + /*
> > + * We failed to charge even after retries, give oom_reaper
> > or
> > + * other process a change to make some free pages.
> > + *
> > + * On non-preemptive, Non-SMP system, this is critical,
> > else
> > + * we keep retrying with no success, forever.
> > + */
> > + cond_resched();
> > +
> > /*
> > * 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
> >
> >
