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Re: [Xen-devel] [RFC][PATCH]Large Page Support for HAP
On 19/11/07 20:27, "Stephen C. Tweedie" <sct@xxxxxxxxxx> wrote:
> It makes me uncomfortable if the guest can't be sure that a PSE request
> isn't actually being honoured by the hardware.
> A guest OS has to go to a lot of trouble to use large pages. Such pages
> upset the normal page recycling of the guest, they are hard to
> recycle... but the guest expects that the compromises are worth it
> because large pages are more efficient at the hardware level.
> So if the HV is only going to supply them on a best-effort basis --- if
> a guest cannot actually rely on a large-page request being honoured ---
> then it's not clear whether this is a net benefit or a net cost to the
An HVM guest always thinks it has big contiguous chunks of RAM. The
superpage mappings get shattered invisibly by the HV in the shadow page
tables only if 2M/4M allocations were not actually possible. This shattering
happens unconditionally right now, so what's being proposed is a net benefit
to HVM guests.
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