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    SubjectRe: [PATCH 0/2] oom, memcg: do not report racy no-eligible OOM
    On Sat 12-01-19 19:52:50, Tetsuo Handa wrote:
    > On 2019/01/12 1:45, Michal Hocko wrote:
    > >>> Anyway, could you update your patch and abstract
    > >>> if (unlikely(tsk_is_oom_victim(current) ||
    > >>> fatal_signal_pending(current) ||
    > >>> current->flags & PF_EXITING))
    > >>>
    > >>> in try_charge and reuse it in mem_cgroup_out_of_memory under the
    > >>> oom_lock with an explanation please?
    > >>
    > >> I don't think doing so makes sense, for
    > >>
    > >> tsk_is_oom_victim(current) = T && fatal_signal_pending(current) == F
    > >>
    > >> can't happen for mem_cgroup_out_of_memory() under the oom_lock, and
    > >> current->flags cannot get PF_EXITING when current is inside
    > >> mem_cgroup_out_of_memory(). fatal_signal_pending(current) alone is
    > >> appropriate for mem_cgroup_out_of_memory() under the oom_lock because
    > >>
    > >> tsk_is_oom_victim(current) = F && fatal_signal_pending(current) == T
    > >>
    > >> can happen there.
    > >
    > > I meant to use the same check consistently. If we can bypass the charge
    > > under a list of conditions in the charge path we should be surely be
    > > able to the the same for the oom path. I will not insist but unless
    > > there is a strong reason I would prefer that.
    > >
    >
    > You mean something like this? I'm not sure this change is safe.
    >
    > mm/memcontrol.c | 27 +++++++++++++++++++++++----
    > 1 file changed, 23 insertions(+), 4 deletions(-)
    >
    > diff --git a/mm/memcontrol.c b/mm/memcontrol.c
    > index 17189da..1733d019 100644
    > --- a/mm/memcontrol.c
    > +++ b/mm/memcontrol.c
    > @@ -248,6 +248,12 @@ enum res_type {
    > iter != NULL; \
    > iter = mem_cgroup_iter(NULL, iter, NULL))
    >
    > +static inline bool can_ignore_limit(void)
    > +{
    > + return tsk_is_oom_victim(current) || fatal_signal_pending(current) ||
    > + (current->flags & PF_EXITING);
    > +}
    > +
    > /* Some nice accessors for the vmpressure. */
    > struct vmpressure *memcg_to_vmpressure(struct mem_cgroup *memcg)
    > {
    > @@ -1395,7 +1401,7 @@ static bool mem_cgroup_out_of_memory(struct mem_cgroup *memcg, gfp_t gfp_mask,
    > * A few threads which were not waiting at mutex_lock_killable() can
    > * fail to bail out. Therefore, check again after holding oom_lock.
    > */
    > - ret = fatal_signal_pending(current) || out_of_memory(&oc);
    > + ret = can_ignore_limit() || out_of_memory(&oc);
    > mutex_unlock(&oom_lock);
    > return ret;
    > }
    > @@ -2215,9 +2230,7 @@ static int try_charge(struct mem_cgroup *memcg, gfp_t gfp_mask,
    > * bypass the last charges so that they can exit quickly and
    > * free their memory.
    > */
    > - if (unlikely(tsk_is_oom_victim(current) ||
    > - fatal_signal_pending(current) ||
    > - current->flags & PF_EXITING))
    > + if (unlikely(can_ignore_limit()))
    > goto force;
    >
    > /*

    I meant something as simple as this, indeed. I would just
    s@can_ignore_limit@should_force_charge@ but this is a minor thing.

    --
    Michal Hocko
    SUSE Labs

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