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Re: Some questions about x86/xen pmap

Manuel Bouyer wrote:
On Thu, May 07, 2009 at 04:15:32PM +0200, Jean-Yves Migeon wrote:
So avoiding the use of APDP under Xen/amd64 would need some re-thinking inside pmap (and more work to get it efficient).

Yes, a completely different way of accessing page table.
That could be the openbsd way, i.e a mapping of all the physical RAM in
the kernel VM space (there's enough VM space to do it)


If we ever support MP with Xen, modifying mappings found in APDP will require a full TLB flush on all CPUs that could use these mappings, which will also be very expensive.

This is a different issue. While porting NetBSD/xen to amd64 I found that
a single 10s or even 100s of distinct APDP operations, each requiring
a map/unmap of ADPD. batching APDP operations would fix most of the performances issues, but I think this needs changes in UVM.

Operations that are required solely by pmap? Or some sort of side effect of jumping back and forth between UVM and pmap? Issue is amd64 specific?

Jean-Yves Migeon

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