Re: [PATCH] memcg, oom: no oom-kill for __GFP_RETRY_MAYFAIL

[Shakeel Butt]

On Mon, Apr 29, 2019 at 5:22 AM Michal Hocko <mhocko@xxxxxxxxxx> wrote:
>
> On Sun 28-04-19 16:56:13, Shakeel Butt wrote:
> > The documentation of __GFP_RETRY_MAYFAIL clearly mentioned that the
> > OOM killer will not be triggered and indeed the page alloc does not
> > invoke OOM killer for such allocations. However we do trigger memcg
> > OOM killer for __GFP_RETRY_MAYFAIL. Fix that.
>
> An example of __GFP_RETRY_MAYFAIL memcg OOM report would be nice. I
> thought we haven't been using that flag for memcg allocations yet.
> But this is definitely good to have addressed.

Actually I am planning to use it for memcg allocations (specifically
fsnotify allocations).

>
> > Signed-off-by: Shakeel Butt <shakeelb@xxxxxxxxxx>
>
> Acked-by: Michal Hocko <mhocko@xxxxxxxx>

Thanks.

>
> > ---
> >  mm/memcontrol.c | 4 +---
> >  1 file changed, 1 insertion(+), 3 deletions(-)
> >
> > diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> > index 2713b45ec3f0..99eca724ed3b 100644
> > --- a/mm/memcontrol.c
> > +++ b/mm/memcontrol.c
> > @@ -2294,7 +2294,6 @@ static int try_charge(struct mem_cgroup *memcg, gfp_t gfp_mask,
> >       unsigned long nr_reclaimed;
> >       bool may_swap = true;
> >       bool drained = false;
> > -     bool oomed = false;
> >       enum oom_status oom_status;
> >
> >       if (mem_cgroup_is_root(memcg))
> > @@ -2381,7 +2380,7 @@ static int try_charge(struct mem_cgroup *memcg, gfp_t gfp_mask,
> >       if (nr_retries--)
> >               goto retry;
> >
> > -     if (gfp_mask & __GFP_RETRY_MAYFAIL && oomed)
> > +     if (gfp_mask & __GFP_RETRY_MAYFAIL)
> >               goto nomem;
> >
> >       if (gfp_mask & __GFP_NOFAIL)
> > @@ -2400,7 +2399,6 @@ static int try_charge(struct mem_cgroup *memcg, gfp_t gfp_mask,
> >       switch (oom_status) {
> >       case OOM_SUCCESS:
> >               nr_retries = MEM_CGROUP_RECLAIM_RETRIES;
> > -             oomed = true;
> >               goto retry;
> >       case OOM_FAILED:
> >               goto force;
> > --
> > 2.21.0.593.g511ec345e18-goog
> >
>
> --
> Michal Hocko
> SUSE Labs