Re: [PATCH v2] mm: memcontrol: remove obsolete comment of mem_cgroup_unmark_under_oom()

[Michal Hocko]

On Wed 30-09-20 01:34:25, linmiaohe wrote:
> Michal Hocko <mhocko@xxxxxxxx> wrote:
> > On Thu 17-09-20 06:59:00, Miaohe Lin wrote:
> >> Since commit 79dfdaccd1d5 ("memcg: make oom_lock 0 and 1 based rather 
> >> than counter"), the mem_cgroup_unmark_under_oom() is added and the 
> >> comment of the mem_cgroup_oom_unlock() is moved here. But this comment 
> >> make no sense here because mem_cgroup_oom_lock() does not operate on under_oom field.
> >
> >OK, so I've looked into this more deeply and I finally remember why we have this comment here. The point is that under_oom shouldn't underflow and that we have to explicitly check for > 0 because a new child memcg could have been added between mem_cgroup_mark_under_oom and mem_cgroup_unmark_under_oom.
> >
> >So the comment makes sense although it is not as helpful as it could be.
> >I think that changing it to the following will be more usefule
> >
> >	/*
> >	 * Be careful about under_oom underflows becase a child memcg
> >	 * could have neem added after mem_cgroup_mark_under_oom
> 
> Should it be s/neem/been/ ?

yep, fat fingers...

> 
> >	 */
> 
> Many thanks for detailed explanation. Will fix it in v2. Thanks again.

-- 
Michal Hocko
SUSE Labs