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[Xen-devel] Re: [PROPOSED REMOVAL] PV guest superpage mappings

To: Dave McCracken <dcm@xxxxxxxx>
Subject: [Xen-devel] Re: [PROPOSED REMOVAL] PV guest superpage mappings
From: Keir Fraser <keir.xen@xxxxxxxxx>
Date: Wed, 20 Jul 2011 17:47:49 +0100
Cc: xen-devel@xxxxxxxxxxxxxxxxxxx, Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
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Thread-topic: [PROPOSED REMOVAL] PV guest superpage mappings
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On 20/07/2011 17:13, "Dave McCracken" <dcm@xxxxxxxx> wrote:

> On Wednesday, July 20, 2011, Keir Fraser wrote:
>> The PV superpage mapping feature has been in the hypervisor for a while
>> now, but I'm not away of any use of this feature by an upstream guest
>> kernel (e.g., and primarily of interest, pv_ops Linux). Am I mistaken, or
>> is anyone looking into or interested in this? If the feature is unused we
>> should remove it from the hypervisor in this development cycle, as it's
>> untested and is nothing more than a maintenance burden and security risk.
>> If the feature is only used by vendor patches, the hypervisor-side
>> implementation belongs in that vendor's patch queues too.
> I submitted a patch to use this feature to Jeremy for inclusion in the Linux
> kernel tree back when it first went into the hypervisor.  I was under the
> impression it was in his tree, and would eventually make its way into mainline
> Linux.
> I must admit I moved on to other projects and did not follow it carefully.
> What is the current path for Xen-specific patches to be included in Linux
> mainline?

You could speak to Konrad about it, who's in your own organisation and might
therefore have similarly aligned interests regarding this feature. I'm
afraid that generally the move has been to the patch authors doing more of
the upstreaming legwork. Otherwise the Xen maintainers end up with piles of
impossible to upstream crud to reimplement themselves.

Apart from Konrad there's also Jeremy of course, and also Stefano Stabellini
and Ian Campbell have been pretty active and may be able to advise.

 -- Keir

> This feature is important for hugepages to work well in a Xen guest.
> Dave McCracken
> Oracle Corp.
> dave.mccracken@xxxxxxxxxx

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