linux-kernel - Re: [PATCH V3 0/8] xen: Switch to virtual mapped linear p2m list

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Message-ID: <546D7751.6060707@suse.com>
Date:	Thu, 20 Nov 2014 06:08:33 +0100
From:	Juergen Gross <jgross@...e.com>
To:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
CC:	linux-kernel@...r.kernel.org, xen-devel@...ts.xensource.com,
	david.vrabel@...rix.com, boris.ostrovsky@...cle.com,
	x86@...nel.org, tglx@...utronix.de, mingo@...hat.com, hpa@...or.com
Subject: Re: [PATCH V3 0/8] xen: Switch to virtual mapped linear p2m list

On 11/19/2014 09:41 PM, Konrad Rzeszutek Wilk wrote:
> On Tue, Nov 11, 2014 at 06:43:38AM +0100, Juergen Gross wrote:
>> Paravirtualized kernels running on Xen use a three level tree for
>> translation of guest specific physical addresses to machine global
>> addresses. This p2m tree is used for construction of page table
>> entries, so the p2m tree walk is performance critical.
>>
>> By using a linear virtual mapped p2m list accesses to p2m elements
>> can be sped up while even simplifying code. To achieve this goal
>> some p2m related initializations have to be performed later in the
>> boot process, as the final p2m list can be set up only after basic
>> memory management functions are available.
>>
>
> Hey Juergen,
>
> I finially finished looking at the patchset. Had some comments,
> some questions that I hope can make it in the patch so that in
> six months or so when somebody looks at the code they can
> understand the subtle pieces.

Yep.

OTOH: What was hard to write should be hard to read ;-)

> Looking forward to the v4! (Thought keep in mind that next week
> is Thanksgiving week so won't be able to look much after Wednesday)

Let's see how testing is going. Setting up the test system wasn't
very smooth due to some unrelated issues.

>
>>   arch/x86/include/asm/pgtable_types.h |    1 +
>>   arch/x86/include/asm/xen/page.h      |   49 +-
>>   arch/x86/mm/pageattr.c               |   20 +
>>   arch/x86/xen/mmu.c                   |   38 +-
>>   arch/x86/xen/p2m.c                   | 1315 ++++++++++++++--------------------
>>   arch/x86/xen/setup.c                 |  460 ++++++------
>>   arch/x86/xen/xen-ops.h               |    6 +-
>>   7 files changed, 854 insertions(+), 1035 deletions(-)
>
> And best of - we are deleting more code!

Indeed. But it's a shame the beautiful ASCII-art in p2m.c is part of the
deletions.


Juergen
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