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Date:   Mon, 27 Sep 2021 17:47:22 -0700
From:   Andrew Morton <akpm@linux-foundation.org>
To:     Huang Ying <ying.huang@intel.com>
Cc:     linux-mm@kvack.org, linux-kernel@vger.kernel.org,
        Thomas Gleixner <tglx@linutronix.de>,
        Dave Hansen <dave.hansen@linux.intel.com>,
        Yang Shi <shy828301@gmail.com>, Zi Yan <ziy@nvidia.com>,
        Michal Hocko <mhocko@suse.com>, Wei Xu <weixugc@google.com>,
        Oscar Salvador <osalvador@suse.de>,
        David Rientjes <rientjes@google.com>,
        Dan Williams <dan.j.williams@intel.com>,
        David Hildenbrand <david@redhat.com>,
        Greg Thelen <gthelen@google.com>,
        Keith Busch <kbusch@kernel.org>
Subject: Re: [PATCH -V2] mm/migrate: fix CPUHP state to update node demotion
 order
Message-Id: <20210927174722.6ca9bc6a63bb50da7754bdaf@linux-foundation.org>
In-Reply-To: <20210927081100.475075-1-ying.huang@intel.com>
References: <20210927081100.475075-1-ying.huang@intel.com>
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On Mon, 27 Sep 2021 16:11:00 +0800 Huang Ying <ying.huang@intel.com> wrote:

> The node demotion order needs to be updated during CPU hotplug.
> Because whether a NUMA node has CPU may influence the demotion order.
> The update function should be called during CPU online/offline after
> the node_states[N_CPU] has been updated.  That is done in
> CPUHP_AP_ONLINE_DYN during CPU online and in CPUHP_MM_VMSTAT_DEAD
> during CPU offline.  But in commit 884a6e5d1f93 ("mm/migrate: update
> node demotion order on hotplug events"), the function to update node
> demotion order is called in CPUHP_AP_ONLINE_DYN during CPU
> online/offline.  This doesn't satisfy the order requirement.

What are the user-visible runtime effects of this error?

>  So in
> this patch, we added CPUHP_AP_MM_DEMOTION_ONLINE and
> CPUHP_MM_DEMOTION_DEAD to be called after CPUHP_AP_ONLINE_DYN and
> CPUHP_MM_VMSTAT_DEAD during CPU online and offline, and register the
> update function on them.
> 
> Fixes: 884a6e5d1f93 ("mm/migrate: update node demotion order on hotplug events")
> Signed-off-by: "Huang, Ying" <ying.huang@intel.com>
> Cc: Thomas Gleixner <tglx@linutronix.de>
> Cc: Dave Hansen <dave.hansen@linux.intel.com>
> Cc: Yang Shi <shy828301@gmail.com>
> Cc: Zi Yan <ziy@nvidia.com>
> Cc: Michal Hocko <mhocko@suse.com>
> Cc: Wei Xu <weixugc@google.com>
> Cc: Oscar Salvador <osalvador@suse.de>
> Cc: David Rientjes <rientjes@google.com>
> Cc: Dan Williams <dan.j.williams@intel.com>
> Cc: David Hildenbrand <david@redhat.com>
> Cc: Greg Thelen <gthelen@google.com>
> Cc: Keith Busch <kbusch@kernel.org>
>