linux-kernel - Re: [PATCH v3 4/5] powerpc/mm: restore top-down allocation when using movable

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Message-Id: <20161004202336.cp7o3772ygfn4o3k@arbab-laptop.austin.ibm.com>
Date:   Tue, 4 Oct 2016 15:23:36 -0500
From:   Reza Arbab <arbab@...ux.vnet.ibm.com>
To:     Balbir Singh <bsingharora@...il.com>
Cc:     Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Michael Ellerman <mpe@...erman.id.au>,
        Paul Mackerras <paulus@...ba.org>,
        Rob Herring <robh+dt@...nel.org>,
        Frank Rowand <frowand.list@...il.com>,
        Jonathan Corbet <corbet@....net>,
        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>,
        linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
        linuxppc-dev@...ts.ozlabs.org, devicetree@...r.kernel.org,
        linux-mm@...ck.org
Subject: Re: [PATCH v3 4/5] powerpc/mm: restore top-down allocation when
 using movable_node

On Tue, Oct 04, 2016 at 11:48:30AM +1100, Balbir Singh wrote:
>On 27/09/16 10:14, Reza Arbab wrote:
>> Right. To be clear, the background info I put in the commit log 
>> refers to x86, where the SRAT can describe movable nodes which exist 
>> at boot.  They're trying to avoid allocations from those nodes before 
>> they've been identified.
>>
>> On power, movable nodes can only exist via hotplug, so that scenario 
>> can't happen. We can immediately go back to top-down allocation. That 
>> is the missing call being added in the patch.
>
>Can we fix cmdline_parse_movable_node() to do the right thing? I 
>suspect that code is heavily x86 only in the sense that no other arch 
>needs it.

Good idea. We could change it so things only go bottom-up on x86 in the 
first place.

A nice consequence is that CONFIG_MOVABLE_NODE would then basically be 
usable on any platform with memory hotplug, not just PPC64 and X86_64.

I'll see if I can move the relevant code into an arch_*() call or 
otherwise factor it out.

-- 
Reza Arbab