On Tue 24-09-19 21:04:58, Baoquan He wrote: > On 09/24/19 at 02:27pm, Michal Hocko wrote: > > On Tue 24-09-19 19:11:51, Baoquan He wrote: > > > diff --git a/mm/memcontrol.c b/mm/memcontrol.c > > > index f3c15bb07cce..84e3fdb1ccb4 100644 > > > --- a/mm/memcontrol.c > > > +++ b/mm/memcontrol.c > > > @@ -4317,6 +4317,9 @@ void mem_cgroup_track_foreign_dirty_slowpath(struct page *page, > > > > > > trace_track_foreign_dirty(page, wb); > > > > > > + if (mem_cgroup_disabled()) > > > + return; > > > + > > > > This doesn't seem correct. We shouldn't even enter the slowpath with > > memcg disabled AFAIC. The check should be done at mem_cgroup_track_foreign_dirty > > level. > > You mean the way in v1 patch, right? It's also fine to me. > > I am worried about the case that memcg is enabled, the checking by > calling mem_cgroup_disabled() will lower efficiency. This is hidden by a static branch so I wouldn't really be worried about the overhead. > And it entering > into mem_cgroup_track_foreign_dirty_slowpath() should be a rare event. But &page->mem_cgroup->css != wb->memcg_css doesn't make any sense when memcg is disabled, right? -- Michal Hocko SUSE Labs
