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Re: [Xen-devel] [PATCH RFC 00/10] Xen balloon page compaction support

On 15/10/14 17:30, Wei Liu wrote:
> On Wed, Oct 15, 2014 at 05:25:41PM +0100, David Vrabel wrote:
>> On 15/10/14 16:54, Wei Liu wrote:
>>> Hi all
>>> This is a prototype to make Xen balloon driver work with balloon page
>>> compaction. The goal is to reduce guest physical address space fragmentation
>>> introduced by balloon pages. Having guest physical address space as 
>>> contiguous
>>> as possible is generally useful (because guest can have higher order 
>>> pages), and
>>> it should also help improve HVM performance (provided that guest kernel 
>>> knows
>>> how to use huge pages -- Linux has hugetlbfs and transparent huge page).
>>> The approach is simple. Core balloon driver is made one of the page sources 
>>> of
>>> Xen balloon driver. Those pages allocated from core balloon driver are 
>>> subject
>>> to balloon page compaction.
>> Your page migrate function is broken.  I'm not going to review anything
>> else in this series until you propose a solution for this.
> What do you think about this idea in general? That's what I care at this
> point. You can skip reviewing at the moment.

In light of Andrew's comments I would like to see a design for the
complete solution, including the parts necessary to coalesce or preserve
superpages in the stage 2 translation tables.

In particular, it looks like page migration will just fragment the stage
2 tables.


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