Re: [RFC PATCH] mm, memory_hotplug: support movable_node for hotplugable nodes

From: Michal Hocko <mhocko@kernel.org>
To: Reza Arbab <arbab@linux.vnet.ibm.com>
Cc: Vlastimil Babka <vbabka@suse.cz>,
	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>,
	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
Date: Thu, 1 Jun 2017 17:38:38 +0200	[thread overview]
Message-ID: <20170601153838.GA8088@dhcp22.suse.cz> (raw)
In-Reply-To: <20170601151935.m5jbfmugocc66qfq@arbab-laptop.localdomain>

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

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