[LTP] [RFC PATCH] mm: memcg/slab: Stop reparented obj_cgroups from charging root

[Michal Koutný]

On Fri, Oct 16, 2020 at 10:53:08AM -0400, Johannes Weiner <hannes@cmpxchg.org> wrote:
> The central try_charge() function charges recursively all the way up
> to and including the root.
Except for use_hiearchy=0 (which is the case here as Richard
wrote). The reparenting is hence somewhat incompatible with
new_parent.use_hiearchy=0 :-/

> We should clean this up one way or another: either charge the root or
> don't, but do it consistently.
I agree this'd be good to unify. One upside of excluding root memcg from
charging is that users are spared from the charging overhead when memcg
tree is not created.  (Actually, I thought that was the reason for this
exception.)

Michal
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