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

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Date:   Thu, 15 Jun 2017 10:16:11 +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 Thu 15-06-17 11:13:54, Wei Yang wrote:
> On Mon, Jun 12, 2017 at 08:45:02AM +0200, Michal Hocko wrote:
> >On Mon 12-06-17 12:28:32, 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).
> >> >
> >> 
> >> When movable_node is enabled, we would have overlapped zones, right?
> >
> >It won't based on this patch. See movable_pfn_range
> >
> 
> Ok, I went through the code and here maybe a question not that close related
> to this patch.

Please start a new thread with unrelated questions

> I did some experiment with qemu+kvm and see this.
> 
> Guest config: 8G RAM, 2 nodes with 4G on each
> Guest kernel: 4.11
> Guest kernel command: kernelcore=1G
> 
> The log message in kernel is:
> 
> [    0.000000] Zone ranges:
> [    0.000000]   DMA      [mem 0x0000000000001000-0x0000000000ffffff]
> [    0.000000]   DMA32    [mem 0x0000000001000000-0x00000000ffffffff]
> [    0.000000]   Normal   [mem 0x0000000100000000-0x000000023fffffff]
> [    0.000000] Movable zone start for each node
> [    0.000000]   Node 0: 0x0000000100000000
> [    0.000000]   Node 1: 0x0000000140000000
> 
> We see on node 2, ZONE_NORMAL overlap with ZONE_MOVABLE. 
> [0x0000000140000000 - 0x000000023fffffff] belongs to both ZONE.

Not really. The above output is just confusing a bit. Zone ranges print
arch_zone_{lowest,highest}_possible_pfn range while the Movable zone
is excluded from that in adjust_zone_range_for_zone_movable
-- 
Michal Hocko
SUSE Labs