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

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Date:   Tue, 25 Oct 2016 19:49:29 -0500
From:   Reza Arbab <arbab@...ux.vnet.ibm.com>
To:     Balbir Singh <bsingharora@...il.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 Wed, Oct 26, 2016 at 09:34:18AM +1100, Balbir Singh wrote:
>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

The movable_node option is x86-only. Both of those nodes contain normal 
memory, so allocations on both are allowed.

>> 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?

As far as I know, power has nothing like the SRAT that tells us, at 
boot, which memory is hotpluggable. So there is nothing to wire the 
movable_node option up to.

Of course, any memory you hotplug afterwards is, by definition, 
hotpluggable. So we can still create movable nodes that way.

-- 
Reza Arbab