linux-kernel - Re: [RFC PATCH] mm, memory_hotplug: support movable

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Message-Id: <20170601154746.wjc56eldgyzr2bpm@arbab-laptop.localdomain>
Date:   Thu, 1 Jun 2017 10:47:46 -0500
From:   Reza Arbab <arbab@...ux.vnet.ibm.com>
To:     Michal Hocko <mhocko@...nel.org>
Cc:     Vlastimil Babka <vbabka@...e.cz>, linux-mm@...ck.org,
        Andrew Morton <akpm@...ux-foundation.org>,
        Mel Gorman <mgorman@...e.de>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Jerome Glisse <jglisse@...hat.com>,
        Yasuaki Ishimatsu <yasu.isimatu@...il.com>,
        qiuxishi@...wei.com, Kani Toshimitsu <toshi.kani@....com>,
        slaoub@...il.com, Joonsoo Kim <js1304@...il.com>,
        Andi Kleen <ak@...ux.intel.com>,
        David Rientjes <rientjes@...gle.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: [RFC PATCH] mm, memory_hotplug: support movable_node for
 hotplugable nodes

On Thu, Jun 01, 2017 at 05:38:38PM +0200, Michal Hocko wrote:
>On Thu 01-06-17 10:19:36, Reza Arbab wrote:
>> The x86 SRAT (or the dt, on other platforms) can describe memory as
>> hotpluggable. See memblock_mark_hotplug(). That's only for memory present at
>> boot, though.
>
>Yes but lose that information after the memblock is gone and numa fully
>initialized. Or can we reconstruct that somehow?

I'm not sure you'd have to. At boot time, those markings are used to 
determine the initial boundaries of ZONE_MOVABLE. So if you removed 
these memblocks, then readded them, they would still be in ZONE_MOVABLE.

>> He's saying that since the memory was added after boot, it is by 
>> definition hotpluggable. There's no need to check for that 
>> marking/description.
>
>Yes, but we do not know whether we are onlining memblocks from a boot
>time numa node or a fresh one which has been hotadded.

That's true.

-- 
Reza Arbab