linux-kernel - Re: [PATCH v6 4/4] of/fdt: mark hotpluggable memory

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Message-ID: <87bmxii85s.fsf@concordia.ellerman.id.au>
Date:   Mon, 14 Nov 2016 22:59:43 +1100
From:   Michael Ellerman <mpe@...erman.id.au>
To:     Reza Arbab <arbab@...ux.vnet.ibm.com>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Rob Herring <robh+dt@...nel.org>,
        Frank Rowand <frowand.list@...il.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>
Cc:     linuxppc-dev@...ts.ozlabs.org, linux-mm@...ck.org,
        devicetree@...r.kernel.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-kernel@...r.kernel.org
Subject: Re: [PATCH v6 4/4] of/fdt: mark hotpluggable memory

Reza Arbab <arbab@...ux.vnet.ibm.com> writes:

> When movable nodes are enabled, any node containing only hotpluggable
> memory is made movable at boot time.
>
> On x86, hotpluggable memory is discovered by parsing the ACPI SRAT,
> making corresponding calls to memblock_mark_hotplug().
>
> If we introduce a dt property to describe memory as hotpluggable,
> configs supporting early fdt may then also do this marking and use
> movable nodes.

So I'm not opposed to this, but it is a little vague.

What does the "hotpluggable" property really mean?

Is it just a hint to the operating system? (which may or may not be
Linux).

Or is it a direction, "this memory must be able to be hotunplugged"?

I think you're intending the former, ie. a hint, which is probably OK.
But it needs to be documented clearly.

cheers