On Tue, Oct 20, 2020 at 6:49 AM Richard Palethorpe <rpalethorpe@xxxxxxx> wrote: > > Hello, > > Richard Palethorpe <rpalethorpe@xxxxxxx> writes: > > > Hello Shakeel, > > > > Shakeel Butt <shakeelb@xxxxxxxxxx> writes: > >>> > >>> V3: Handle common case where use_hierarchy=1 and update description. > >>> > >>> mm/memcontrol.c | 7 +++++-- > >>> 1 file changed, 5 insertions(+), 2 deletions(-) > >>> > >>> diff --git a/mm/memcontrol.c b/mm/memcontrol.c > >>> index 6877c765b8d0..34b8c4a66853 100644 > >>> --- a/mm/memcontrol.c > >>> +++ b/mm/memcontrol.c > >>> @@ -291,7 +291,7 @@ static void obj_cgroup_release(struct percpu_ref *ref) > >>> > >>> spin_lock_irqsave(&css_set_lock, flags); > >>> memcg = obj_cgroup_memcg(objcg); > >>> - if (nr_pages) > >>> + if (nr_pages && (!mem_cgroup_is_root(memcg) || memcg->use_hierarchy)) > >> > >> If we have non-root memcg with use_hierarchy as 0 and this objcg was > >> reparented then this __memcg_kmem_uncharge() can potentially underflow > >> the page counter and give the same warning. > > > > Yes, although the kernel considers such a config to be broken, and > > prints a warning to the log, it does allow it. > > Actually this can not happen because if use_hierarchy=0 then the objcg > will be reparented to root. > Yup, you are right. I do wonder if we should completely deprecate use_hierarchy=0.
