linux-kernel - Re: [PATCH] mm: memcontrol: skip propagate percpu vmstat values to current memcg

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Message-ID: <YAcPwhl//jF/WpHu@cmpxchg.org>
Date:   Tue, 19 Jan 2021 11:58:42 -0500
From:   Johannes Weiner <hannes@...xchg.org>
To:     Muchun Song <songmuchun@...edance.com>
Cc:     mhocko@...nel.org, vdavydov.dev@...il.com,
        akpm@...ux-foundation.org, cgroups@...r.kernel.org,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm: memcontrol: skip propagate percpu vmstat values to
 current memcg

On Tue, Jan 19, 2021 at 01:27:44PM +0800, Muchun Song wrote:
> The current memcg will be freed soon, so updating it's vmstat and
> vmevent values is pointless. Just skip updating it.
> 
> Signed-off-by: Muchun Song <songmuchun@...edance.com>

Oof, that's pretty subtle! Somebody trying to refactor that code for
other purposes may not immediately notice that optimization and add
potentially tedious bugs.

How much does this save? Cgroup creation and deletion isn't really
considered a hot path. It takes global locks and such...