Date: Thu, 1 Jun 2017 16:22:28 +0200
From: Michal Hocko <mhocko@kernel.org>
To: Vlastimil Babka <vbabka@suse.cz>
Cc: linux-mm@kvack.org, Andrew Morton <akpm@linux-foundation.org>,
        Mel Gorman <mgorman@suse.de>, Andrea Arcangeli <aarcange@redhat.com>,
        Jerome Glisse <jglisse@redhat.com>,
        Reza Arbab <arbab@linux.vnet.ibm.com>,
        Yasuaki Ishimatsu <yasu.isimatu@gmail.com>, qiuxishi@huawei.com,
        Kani Toshimitsu <toshi.kani@hpe.com>, slaoub@gmail.com,
        Joonsoo Kim <js1304@gmail.com>, Andi Kleen <ak@linux.intel.com>,
        David Rientjes <rientjes@google.com>,
        Daniel Kiper <daniel.kiper@oracle.com>,
        Igor Mammedov <imammedo@redhat.com>,
        Vitaly Kuznetsov <vkuznets@redhat.com>,
        LKML <linux-kernel@vger.kernel.org>
Subject: Re: [RFC PATCH] mm, memory_hotplug: support movable_node for
 hotplugable nodes
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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