Re: [PATCH v2 2/2] xen/setup: Remap Xen Identity Mapped RAM

From: Matthew Rushton
Date: Tue Aug 26 2014 - 16:40:33 EST

On 08/01/14 07:52, 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

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

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.

I will remove this patch from the queue for 3.17.

Have you had a chance to try the v3 patch set?

To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at
Please read the FAQ at