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

[Matt Wilson <msw@xxxxxxxxx>]

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?

--msw

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