linux-kernel - Re: [PATCH 2/2] mm, memory_hotplug: remove zone restrictions

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Date:   Fri, 30 Jun 2017 17:39:56 +0800
From:   Wei Yang <richard.weiyang@...il.com>
To:     Michal Hocko <mhocko@...nel.org>
Cc:     Linux-MM <linux-mm@...ck.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Mel Gorman <mgorman@...e.de>, Vlastimil Babka <vbabka@...e.cz>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Reza Arbab <arbab@...ux.vnet.ibm.com>,
        Yasuaki Ishimatsu <yasu.isimatu@...il.com>,
        Xishi Qiu <qiuxishi@...wei.com>,
        Kani Toshimitsu <toshi.kani@....com>, slaoub@...il.com,
        Joonsoo Kim <js1304@...il.com>,
        Daniel Kiper <daniel.kiper@...cle.com>,
        Igor Mammedov <imammedo@...hat.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/2] mm, memory_hotplug: remove zone restrictions

On Fri, Jun 30, 2017 at 4:39 PM, Michal Hocko <mhocko@...nel.org> wrote:
> On Fri 30-06-17 11:09:51, Wei Yang wrote:
>> On Thu, Jun 29, 2017 at 3:35 PM, Michal Hocko <mhocko@...nel.org> wrote:
>> > From: Michal Hocko <mhocko@...e.com>
>> >
>>
>> Michal,
>>
>> I love the idea very much.
>>

>
> You haven't written your sequence of onlining but if you used the same
> one as mentioned in the patch then you should get
> memory34/valid_zones:Normal
> memory35/valid_zones:Normal Movable
> memory36/valid_zones:Normal Movable
> memory37/valid_zones:Normal Movable
> memory38/valid_zones:Normal Movable
> memory39/valid_zones:Normal
> memory40/valid_zones:Movable Normal
> memory41/valid_zones:Movable Normal
>
> Even if you kept 37 as movable and offline 38 you wouldn't get 38-41
> movable by default because...
>

Yes, it depends on the zone range.

>> The reason is the same, we don't adjust the zone's range when offline
>> memory.
>
> .. of this.
>
>> This is also a known issue?
>
> yes and to be honest I do not plan to fix it unless somebody has a real
> life usecase for it. Now that we allow explicit onlininig type anywhere
> it seems like a reasonable behavior and this will allow us to remove
> quite some code which is always a good deal wrt longterm maintenance.
>

hmm... the statistics displayed in /proc/zoneinfo would be meaningless
for zone_normal and zone_movable.

I am not sure, maybe no one care about these fields.

> Thanks!
> --
> Michal Hocko
> SUSE Labs