Subject: Re: [PATCH v4 4/5] mm: make processing of movable_node arch-specific
To: Reza Arbab <arbab@linux.vnet.ibm.com>
References: <1475778995-1420-1-git-send-email-arbab@linux.vnet.ibm.com>
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 <235f2d20-cf84-08df-1fb4-08ee258fdc52@gmail.com>
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Cc: Michael Ellerman <mpe@ellerman.id.au>,
        Benjamin Herrenschmidt <benh@kernel.crashing.org>,
        Paul Mackerras <paulus@samba.org>, Rob Herring <robh+dt@kernel.org>,
        Frank Rowand <frowand.list@gmail.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Bharata B Rao <bharata@linux.vnet.ibm.com>,
        Nathan Fontenot <nfont@linux.vnet.ibm.com>,
        Stewart Smith <stewart@linux.vnet.ibm.com>,
        Alistair Popple <apopple@au1.ibm.com>,
        "Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com>,
        Tang Chen <tangchen@cn.fujitsu.com>, linux-kernel@vger.kernel.org,
        linuxppc-dev@lists.ozlabs.org, devicetree@vger.kernel.org,
        linux-mm@kvack.org
From: Balbir Singh <bsingharora@gmail.com>
Message-ID: <13f4f7fa-77b7-0924-f47c-5e55af8269d0@gmail.com>
Date: Wed, 26 Oct 2016 09:59:40 +1100
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On 26/10/16 02:55, Reza Arbab wrote:
> On Tue, Oct 25, 2016 at 11:15:40PM +1100, Balbir Singh wrote:
>> After the ack, I realized there were some more checks needed, IOW
>> questions for you :)
> 
> Hey! No takebacks!
> 

I still believe we need your changes, I was wondering if we've tested
it against normal memory nodes and checked if any memblock
allocations end up there. Michael showed me some memblock
allocations on node 1 of a two node machine with movable_node
I'll double check at my end. See my question below


> The short answer is that neither of these is a concern.
> 
> Longer; if you use "movable_node", x86 can identify these nodes at boot. They call memblock_mark_hotplug() while parsing the SRAT. Then, when the zones are initialized, those markings are used to determine ZONE_MOVABLE.
> 
> We have no analog of this SRAT information, so our movable nodes can only be created post boot, by hotplugging and explicitly onlining with online_movable.
>

Is this true for all of system memory as well or only for nodes
hotplugged later?

Balbir Singh.