Re: [PATCH 2/2] mm: vmpressure: use mem_cgroup_is_root API

[Yang Shi]

On 2/12/20 12:23 AM, Michal Hocko wrote:
> On Tue 11-02-20 13:24:09, Yang Shi wrote:
> > Use mem_cgroup_is_root() API to check if memcg is root memcg instead of
> > open coding.
> Yes, the direct use outside of memcontrol.c should be really an
> exception. The only other similar case is cgwb_bdi_init and there is no
> easy way to replace - except for adding a helper which is not worth it.

Yes, it seems so. cgwb_bdi_init just deferences root_mem_cgroup to 
access its css. It is the only user outside memcontrol.c, so I agree a 
helper for it might be overkilling. Once we have more users, it should 
be considered.

> > Signed-off-by: Yang Shi <yang.shi@xxxxxxxxxxxxxxxxx>
> Acked-by: Michal Hocko <mhocko@xxxxxxxx>

Thanks.

> Thanks!
>
> > ---
> >   mm/vmpressure.c | 2 +-
> >   1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/mm/vmpressure.c b/mm/vmpressure.c
> > index 0590f00..d69019f 100644
> > --- a/mm/vmpressure.c
> > +++ b/mm/vmpressure.c
> > @@ -280,7 +280,7 @@ void vmpressure(gfp_t gfp, struct mem_cgroup *memcg, bool tree,
> >   		enum vmpressure_levels level;
> >   
> >   		/* For now, no users for root-level efficiency */
> > -		if (!memcg || memcg == root_mem_cgroup)
> > +		if (!memcg || mem_cgroup_is_root(memcg))
> >   			return;
> >   
> >   		spin_lock(&vmpr->sr_lock);
> > --
> > 1.8.3.1