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

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Message-Id: <20161025155507.37kv5akdlgo6m2be@arbab-laptop.austin.ibm.com>
Date:   Tue, 25 Oct 2016 10:55:07 -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 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!

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.

>1. Have you checked to see if our memblock allocations spill
>over to probably hotpluggable nodes?

Since our nodes don't exist at boot, we don't have that short window 
before the zones are drawn where the node has normal memory, and a 
kernel allocation might occur within.

>2. Shouldn't we be marking nodes discovered as movable via
>memblock_mark_hotplug()?

Again, this early boot marking mechanism only applies to movable_node.

-- 
Reza Arbab