[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: [Xen-devel] [PATCH][HVM] Removing 1:1 mapping from qemu-dm

On 28 Jun 2006, at 16:15, Nakajima, Jun wrote:

Since the write refcount in type_info can change at any time now because
of map/unmap by qemu-dm at runtime, I stopped using it to avoid a hack
in mm.c. The extra code is a scaled-down version of write refcount
dedicated for guest page table pages, and I think 4 bits would be
sufficient in normal cases because normal guests don't establish that
many translations (i.e. using different virtual addresses) against page
table pages.

Since the number cannot exceed the length of the shadow hash chains
anyway, I can add an extra logic that detects overflow and scans the
entire chains if detected. With this we can just have a 2-bit ref count,
0 - no, 1 (most cases), and 2 - more than one.

I'd prefer the hack in mm.c I think. It's certainly much smaller, and it'd be okay with a comment. Is there any way for get/put_page_type to know if they've been called on a shadow page (as opposed to a guest page) and to avoid changing the type count based on that, rather than whether the page is local or foreign? That'd be a neater and less hacky thing to use for the decision imo.

 -- Keir

Xen-devel mailing list



Lists.xenproject.org is hosted with RackSpace, monitoring our
servers 24x7x365 and backed by RackSpace's Fanatical Support®.