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. > >> >> We never set root_mem_cgroup->objcg, so, no need to check for root > > I don't think that is relevant as we get the memcg from objcg->memcg > which is set during reparenting. I suppose however, we can determine if > the objcg was reparented by inspecting memcg->objcg. > >> here. I think checking just memcg->use_hierarchy should be sufficient. > > If we just check use_hierarchy then objects directly charged to the > memcg where use_hierarchy=0 will not be uncharged. However, maybe it is > better to check if it was reparented and if use_hierarchy=0. -- Thank you, Richard.
