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Re: [Xen-devel] [RFC PATCH] page_alloc: use first half of higher order chunks when halving

On 04/16/14 07:15, Konrad Rzeszutek Wilk wrote:
On Mon, Apr 14, 2014 at 04:34:47PM +0100, Jan Beulich wrote:
On 14.04.14 at 16:40, <konrad.wilk@xxxxxxxxxx> wrote:
That was OK, but the M2P lookup table was not too thrilled with this.
Perhaps I should have used another hypercall to re-arrange the M2P?
I think I did try 'XENMEM_exchange' but that is not the right call either.
Yeah, that's allocating new pages in exchange for your old ones. Not
really what you want.

Perhaps I should use XENMEM_remove_from_physmap/XENMEM_add_to_physmap
combo ?
A pair of MMU_MACHPHYS_UPDATE operations would seem to be the
right way of doing this (along with respective kernel internal accounting
like set_phys_to_machine(), and perhaps a pair of update_va_mapping
operations if the 1:1 map is already in place at that time, and you care
about which page contents appears at which virtual address).

Matt & Matthew - my plate is quite filled and I fear that in the next three
weeks there is not going to be much time to code up a prototype.

Would either one of you be willing to take a crack at this? It would
be neat as we could remove a lot of the balloon increase/decrease code
in arch/x86/xen/setup.c.


I have a first pass at this. Just need to test it and should have something ready sometime next week or so.


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