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Subject: Re: [PATCH 3/6] mm/page_alloc: Adjust pcp->high after CPU hotplug
 events
To:     Mel Gorman <mgorman@techsingularity.net>,
        Andrew Morton <akpm@linux-foundation.org>
Cc:     Hillf Danton <hdanton@sina.com>,
        Dave Hansen <dave.hansen@linux.intel.com>,
        Michal Hocko <mhocko@kernel.org>,
        LKML <linux-kernel@vger.kernel.org>,
        Linux-MM <linux-mm@kvack.org>
References: <20210525080119.5455-1-mgorman@techsingularity.net>
 <20210525080119.5455-4-mgorman@techsingularity.net>
From:   Vlastimil Babka <vbabka@suse.cz>
Message-ID: <7b457a8b-877b-1644-9709-68a67cd27b60@suse.cz>
Date:   Fri, 28 May 2021 13:08:40 +0200
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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@techsingularity.net>

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