Re: [PATCH v2 2/2] xen/setup: Remap Xen Identity Mapped RAM
From: Matthew Rushton
Date: Mon Aug 11 2014 - 13:40:52 EST
On 08/01/14 08:56, Boris Ostrovsky wrote:
On 08/01/2014 11:52 AM, Matt Wilson wrote:
On Fri, Aug 01, 2014 at 03:52:28PM +0100, David Vrabel wrote:
On 31/07/14 18:43, David Vrabel wrote:
On 20/07/14 01:01, 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
Applied to devel/for-linus-3.17
Unfortunately, this produces too many WARNINGs on some boxes or
with certain configurations.
Hi David,
Do you have more information about the systems or configurations that
showed a problem?
This appears to be happening on 32-bit dom0.
-boris
I just pushed a v3 version of the patch set which should fix the issue.
There was casting issue that would affect 32-bit builds.
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