Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
Date:   Wed, 12 Oct 2022 13:41:01 +0100
From:   Aaron Tomlin <atomlin@redhat.com>
To:     Hillf Danton <hdanton@sina.com>
Cc:     frederic@kernel.org, mtosatti@redhat.com,
        linux-kernel@vger.kernel.org, linux-mm@kvack.org,
        atomlin@atomlin.com
Subject: Re: [PATCH v8 5/5] tick/sched: Ensure quiet_vmstat() is called when
 the idle tick was stopped too
Message-ID: <20221012124101.zod6m2brlzpgx6nb@ava.usersys.com>
References: <20220924152227.819815-1-atomlin@redhat.com>
 <20220925010511.1482-1-hdanton@sina.com>
 <20221003124435.1769-1-hdanton@sina.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=utf-8
Content-Disposition: inline
In-Reply-To: <20221003124435.1769-1-hdanton@sina.com>
Precedence: bulk

> Given work canceled because per-CPU pages can be freed remotely from
> housekeeping CPUs (see patch 3/5), what is added here is not needed.

Hi Hillf,

Firstly, apologies for the delay!

The concern is to ensure CPU-specific vmstat counters are reset and folded
into NUMA node and zone specific and global counters too before entering
idle. It is necessary to invoke quiet_vmstat() on return to idle even if
the scheduling-clock tick has been previously stopped.
Please refer to the complete scenario I described again.

If I understand correctly, indeed the remote drain/or free of zone
CPU-specific pages can be initiated by a "housekeeping" CPU i.e.
refresh_cpu_vm_stats(true) via a worker thread/or kworker, yet the actual
free will only occur when the nohz_full CPU exits idle code and calls
schedule_idle().


Kind regards,

-- 
Aaron Tomlin