linux-kernel - Re: [PATCH 3/6] mm/page_alloc: Adjust pcp->high after CPU hotplug events

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Date:   Fri, 28 May 2021 13:08:40 +0200
From:   Vlastimil Babka <vbabka@...e.cz>
To:     Mel Gorman <mgorman@...hsingularity.net>,
        Andrew Morton <akpm@...ux-foundation.org>
Cc:     Hillf Danton <hdanton@...a.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Michal Hocko <mhocko@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Linux-MM <linux-mm@...ck.org>
Subject: Re: [PATCH 3/6] mm/page_alloc: Adjust pcp->high after CPU hotplug
 events

On 5/25/21 10:01 AM, Mel Gorman wrote:
> The PCP high watermark is based on the number of online CPUs so the
> watermarks must be adjusted during CPU hotplug. At the time of
> hot-remove, the number of online CPUs is already adjusted but during
> hot-add, a delta needs to be applied to update PCP to the correct
> value. After this patch is applied, the high watermarks are adjusted
> correctly.
> 
>   # grep high: /proc/zoneinfo  | tail -1
>               high:  649
>   # echo 0 > /sys/devices/system/cpu/cpu4/online
>   # grep high: /proc/zoneinfo  | tail -1
>               high:  664
>   # echo 1 > /sys/devices/system/cpu/cpu4/online
>   # grep high: /proc/zoneinfo  | tail -1
>               high:  649
> 
> Signed-off-by: Mel Gorman <mgorman@...hsingularity.net>

Acked-by: Vlastimil Babka <vbabka@...e.cz>