Re: [PATCH v5 09/11] mm: memcontrol: use obj_cgroup APIs to charge the LRU pages

[Muchun Song]

On Wed, Jun 01, 2022 at 07:34:38PM +0200, Michal Koutný wrote:
> Hello Muchun.
> 
> On Mon, May 30, 2022 at 03:49:17PM +0800, Muchun Song <songmuchun@xxxxxxxxxxxxx> wrote:
> > +static inline bool obj_cgroup_is_root(struct obj_cgroup *objcg)
> > +{
> > +	return objcg == root_obj_cgroup;
> > +}
> 
> Admittedly, this predicate alone caught my eye, why it did not also
> check root_mem_cgroup->objcg_list.
> However, deeper look reveals it's purpose is to avoid missing uncharges
> of pages that were charged in non-root memcg and later re-associated
> upwards after reparenting.

Right.

> So it's like obj_cgroup_root_origin() (I'm not suggesting a rename, just
> illustrating the understanding).
> 
> get_obj_cgroup_from_current() gains some complexity but it still holds
> that in root memcg neither kernel objects nor LRU pages are charged.
> At the same time, reparented kernel objects or LRU pages are properly
> uncharged.
> 
> These parts are 
> Reviewed-by: Michal Koutný <mkoutny@xxxxxxxx>
> 

Thanks Michal.

> (I did not look into the locking guarantees with the new API though.)
> 
>