linux-kernel - Re: [PATCH v4 4/5] mm: make processing of movable

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Message-ID: <112504e9-561d-e0da-7a40-73996c678b56@gmail.com>
Date:   Wed, 26 Oct 2016 09:34:18 +1100
From:   Balbir Singh <bsingharora@...il.com>
To:     Reza Arbab <arbab@...ux.vnet.ibm.com>
Cc:     Michael Ellerman <mpe@...erman.id.au>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Rob Herring <robh+dt@...nel.org>,
        Frank Rowand <frowand.list@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Bharata B Rao <bharata@...ux.vnet.ibm.com>,
        Nathan Fontenot <nfont@...ux.vnet.ibm.com>,
        Stewart Smith <stewart@...ux.vnet.ibm.com>,
        Alistair Popple <apopple@....ibm.com>,
        "Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>,
        Tang Chen <tangchen@...fujitsu.com>,
        linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
        devicetree@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH v4 4/5] mm: make processing of movable_node arch-specific



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.