linux-kernel - Re: [PATCH v3 5/5] mm: enable CONFIG_MOVABLE

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Date:   Mon, 26 Sep 2016 19:19:19 -0500
From:   Reza Arbab <arbab@...ux.vnet.ibm.com>
To:     Benjamin Herrenschmidt <benh@...nel.crashing.org>
Cc:     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>,
        Balbir Singh <bsingharora@...il.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 5/5] mm: enable CONFIG_MOVABLE_NODE on powerpc

On Tue, Sep 27, 2016 at 07:15:41AM +1000, Benjamin Herrenschmidt wrote:
>What is that business with a command line argument ? Do that mean that
>we'll need some magic command line argument to properly handle LPC memory
>on CAPI devices or GPUs ? If yes that's bad ... kernel arguments should
>be a last resort.

Well, movable_node is just a boolean, meaning "allow nodes which contain 
only movable memory". It's _not_ like "movable_node=10,13-15,17", if 
that's what you were thinking.

>We should have all the information we need from the device-tree.
>
>Note also that we shouldn't need to create those nodes at boot time,
>we need to add the ability to create the whole thing at runtime, we may know
>that there's an NPU with an LPC window in the system but we won't know if it's
>used until it is and for CAPI we just simply don't know until some PCI device
>gets turned into CAPI mode and starts claiming LPC memory...

Yes, this is what is planned for, if I'm understanding you correctly.

In the dt, the PCI device node has a phandle pointing to the memory 
node. The memory node describes the window into which we can hotplug at 
runtime.

-- 
Reza Arbab