linux-kernel - Re: [PATCH] memcg: avoid refill

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Message-ID: <20250313153910.GA1252169@cmpxchg.org>
Date: Thu, 13 Mar 2025 11:39:10 -0400
From: Johannes Weiner <hannes@...xchg.org>
To: Shakeel Butt <shakeel.butt@...ux.dev>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
	Michal Hocko <mhocko@...nel.org>,
	Roman Gushchin <roman.gushchin@...ux.dev>,
	Muchun Song <muchun.song@...ux.dev>, linux-mm@...ck.org,
	cgroups@...r.kernel.org, linux-kernel@...r.kernel.org,
	Meta kernel team <kernel-team@...a.com>
Subject: Re: [PATCH] memcg: avoid refill_stock for root memcg

On Wed, Mar 12, 2025 at 10:48:12PM -0700, Shakeel Butt wrote:
> We never charge the page counters of root memcg, so there is no need to
> put root memcg in the memcg stock. At the moment, refill_stock() can be
> called from try_charge_memcg(), obj_cgroup_uncharge_pages() and
> mem_cgroup_uncharge_skmem().
> 
> The try_charge_memcg() and mem_cgroup_uncharge_skmem() are never called
> with root memcg, so those are fine. However obj_cgroup_uncharge_pages()
> can potentially call refill_stock() with root memcg if the objcg object
> has been reparented over to the root memcg. Let's just avoid
> refill_stock() from obj_cgroup_uncharge_pages() for root memcg.
> 
> Signed-off-by: Shakeel Butt <shakeel.butt@...ux.dev>

Acked-by: Johannes Weiner <hannes@...xchg.org>