linux-kernel - Re: [PATCH v3 6/6] mm: refactor memcg_hotplug_cpu_dead() to use memcg_flush_offline

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Message-ID: <20190313194846.GA6683@cmpxchg.org>
Date:   Wed, 13 Mar 2019 15:48:46 -0400
From:   Johannes Weiner <hannes@...xchg.org>
To:     Roman Gushchin <guroan@...il.com>
Cc:     linux-mm@...ck.org, kernel-team@...com,
        linux-kernel@...r.kernel.org, Tejun Heo <tj@...nel.org>,
        Rik van Riel <riel@...riel.com>,
        Michal Hocko <mhocko@...nel.org>, Roman Gushchin <guro@...com>
Subject: Re: [PATCH v3 6/6] mm: refactor memcg_hotplug_cpu_dead() to use
 memcg_flush_offline_percpu()

On Wed, Mar 13, 2019 at 11:39:53AM -0700, Roman Gushchin wrote:
> It's possible to remove a big chunk of the redundant code by making
> memcg_flush_offline_percpu() to take cpumask as an argument and flush
> percpu data on all cpus belonging to the mask instead of all possible cpus.
> 
> Then memcg_hotplug_cpu_dead() can call it with a single CPU bit set.
> 
> This approach allows to remove all duplicated code, but safe the
> performance optimization made in memcg_flush_offline_percpu():
> only one atomic operation per data entry.
> 
> for_each_data_entry()
> 	for_each_cpu(cpu. cpumask)
> 		sum_events()
> 	flush()
> 
> Otherwise it would be one atomic operation per data entry per cpu:
> for_each_cpu(cpu)
> 	for_each_data_entry()
> 		flush()
> 
> Signed-off-by: Roman Gushchin <guro@...com>

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