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

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Message-ID: <20170612063713.GC4145@dhcp22.suse.cz>
Date:   Mon, 12 Jun 2017 08:37:13 +0200
From:   Michal Hocko <mhocko@...nel.org>
To:     Wei Yang <richard.weiyang@...il.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
        Mel Gorman <mgorman@...e.de>, Vlastimil Babka <vbabka@...e.cz>,
        Andrea Arcangeli <aarcange@...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: [PATCH] mm, memory_hotplug: support movable_node for hotplugable
 nodes

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@...e.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