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Date:	Mon, 11 Aug 2014 12:00:51 -0700
From:	Matthew Rushton <>
To:	Matt Wilson <>
	Matt Rushton <>
Subject: Re: [PATCH v3 2/2] xen/setup: Remap Xen Identity Mapped RAM

On 08/11/14 10:41, Matt Wilson wrote:
> On Mon, Aug 11, 2014 at 10:34:01AM -0700, Matt Rushton wrote:
>> Instead of ballooning up and down dom0 memory this remaps the existing mfns
>> that were replaced by the identity map. The reason for this is that the
>> existing implementation ballooned memory up and and down which caused dom0
>> to have discontiguous pages. In some cases this resulted in the use of bounce
>> buffers which reduced network I/O performance significantly. This change will
>> honor the existing order of the pages with the exception of some boundary
>> conditions.
>> To do this we need to update both the Linux p2m table and the Xen m2p table.
>> Particular care must be taken when updating the p2m table since it's important
>> to limit table memory consumption and reuse the existing leaf pages which get
>> freed when an entire leaf page is set to the identity map. To implement this,
>> mapping updates are grouped into blocks with table entries getting cached
>> temporarily and then released.
>> On my test system before:
>> Total pages: 2105014
>> Total contiguous: 1640635
>> After:
>> Total pages: 2105014
>> Total contiguous: 2098904
>> Signed-off-by: Matthew Rushton <>
>> ---
> Matt,
> Could you provide a summary of v2->v3 changes here?
> --msw
>>   arch/x86/xen/p2m.c   |   23 +---
>>   arch/x86/xen/p2m.h   |   15 ++
>>   arch/x86/xen/setup.c |  370 +++++++++++++++++++++++++++++++++++++++-----------
>>   3 files changed, 314 insertions(+), 94 deletions(-)
>>   create mode 100644 arch/x86/xen/p2m.h
Resent patch set with:

v3: One line change to fix 32-bit mfn casting issue with MMU_MACHPHYS_UPDATE

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