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

From: Michal Hocko <mhocko@kernel.org>
To: Wei Yang <richard.weiyang@gmail.com>
Cc: Andrew Morton <akpm@linux-foundation.org>,
	linux-mm@kvack.org, Mel Gorman <mgorman@suse.de>,
	Vlastimil Babka <vbabka@suse.cz>,
	Andrea Arcangeli <aarcange@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: [PATCH] mm, memory_hotplug: support movable_node for hotplugable nodes
Date: Mon, 12 Jun 2017 08:37:13 +0200	[thread overview]
Message-ID: <20170612063713.GC4145@dhcp22.suse.cz> (raw)
In-Reply-To: <20170611014535.GA6206@WeideMBP.lan>

On Sun 11-06-17 09:45:35, Wei Yang wrote:
> On Thu, Jun 08, 2017 at 02:23:18PM +0200, Michal Hocko wrote:
> >From: Michal Hocko <mhocko@suse.com>
> >
> >movable_node kernel parameter allows to make hotplugable NUMA
> >nodes to put all the hotplugable memory into movable zone which
> >allows more or less reliable memory hotremove.  At least this
> >is the case for the NUMA nodes present during the boot (see
> >find_zone_movable_pfns_for_nodes).
> >
> >This is not the case for the memory hotplug, though.
> >
> >	echo online > /sys/devices/system/memory/memoryXYZ/status
> >
> >will default to a kernel zone (usually ZONE_NORMAL) unless the
> >particular memblock is already in the movable zone range which is not
> >the case normally when onlining the memory from the udev rule context
> >for a freshly hotadded NUMA node. The only option currently is to have a
> >special udev rule to echo online_movable to all memblocks belonging to
> >such a node which is rather clumsy. Not the mention this is inconsistent
> >as well because what ended up in the movable zone during the boot will
> >end up in a kernel zone after hotremove & hotadd without special care.
> >
> 
> A kernel zone here means? Which is the counterpart in zone_type? or a
> combination of several zone_type?

Any zone but < ZONE_HIGHMEM. The specific zone depends on the placement.
But it is ZONE_NORMAL in most situations.

-- 
Michal Hocko
SUSE Labs

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