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

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Message-ID: <20170601153838.GA8088@dhcp22.suse.cz>
Date:   Thu, 1 Jun 2017 17:38:38 +0200
From:   Michal Hocko <mhocko@...nel.org>
To:     Reza Arbab <arbab@...ux.vnet.ibm.com>
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 01-06-17 10:19:36, Reza Arbab wrote:
> On Thu, Jun 01, 2017 at 04:22:28PM +0200, Michal Hocko wrote:
> >On Thu 01-06-17 16:11:55, Vlastimil Babka wrote:
> >>Simple should work, hopefully.
> >>- if memory is hotplugged, it's obviously hotplugable, so we don't have
> >>to rely on BIOS description.
> >
> >Not sure I understand. We do not have any information about the hotplug
> >status at the time we do online.
> 
> 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?

> 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.
-- 
Michal Hocko
SUSE Labs