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

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Message-ID: <20170615031354.GC16833@WeideMacBook-Pro.local>
Date:   Thu, 15 Jun 2017 11:13:54 +0800
From:   Wei Yang <richard.weiyang@...il.com>
To:     Michal Hocko <mhocko@...nel.org>
Cc:     Wei Yang <richard.weiyang@...il.com>,
        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 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.

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.

My confusion is:

After we enable ZONE_MOVABLE, no matter whether it is enabled by
"movable_node" or "kernelcore", we would face this kind of overlap? 
Finally, the pages in the overlapped range be belongs to which ZONE?

-- 
Wei Yang
Help you, Help me

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