linux-kernel - Re: [PATCH v3 2/2] xen/setup: Remap Xen Identity Mapped RAM

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Date:	Mon, 11 Aug 2014 10:41:26 -0700
From:	Matt Wilson <msw@...ux.com>
To:	Matt Rushton <mvrushton@...il.com>
Cc:	konrad.wilk@...cle.com, boris.ostrovsky@...cle.com,
	david.vrabel@...rix.com, msw@...zon.com,
	linux-kernel@...r.kernel.org, xen-devel@...ts.xensource.com,
	Matt Rushton <mrushton@...zon.com>
Subject: Re: [PATCH v3 2/2] xen/setup: Remap Xen Identity Mapped RAM

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 <mrushton@...zon.com>
> ---

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
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