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

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Date:   Thu, 1 Jun 2017 16:22:28 +0200
From:   Michal Hocko <mhocko@...nel.org>
To:     Vlastimil Babka <vbabka@...e.cz>
Cc:     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>,
        Reza Arbab <arbab@...ux.vnet.ibm.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 16:11:55, Vlastimil Babka wrote:
> On 06/01/2017 02:20 PM, Michal Hocko wrote:
[...]
> > Strictly speaking the semantic is not identical with the boot time
> > initialization because find_zone_movable_pfns_for_nodes covers only the
> > hotplugable range as described by the BIOS/FW. From my experience this
> > is usually a full node though (except for Node0 which is special and
> > never goes away completely). If this turns out to be a problem in the
> > real life we can tweak the code to store hotplug flag into memblocks
> > but let's keep this simple now.
> 
> 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.

> - there shouldn't be a reason to offline a non-removable (part of) node
> and online it back (which would move it from Normal to Movable after
> your patch?), right?

not really. If the memblock was inside a kernel zone it will stay there
with a new online operation because we check for that explicitly.
-- 
Michal Hocko
SUSE Labs