Re: [Xen-devel] [PATCH] ioemu: directly project all memory on x86_64

[Keir Fraser <Keir.Fraser@xxxxxxxxxxxx>]

On 23/1/08 16:38, "Samuel Thibault" <samuel.thibault@xxxxxxxxxxxxx> wrote:

> Keir Fraser, le Wed 23 Jan 2008 16:30:27 +0000, a écrit :
>> I don't really want the memory-size parameter back. What if we support
>> memory hotplug in future (e.g., we could do now if the guest decides to
>> balloon in some memory higher up in its memory map)?
> 
> Well, the question holds for ia64 too, which already projects all
> memory.

Sure. I expect ia64 lags behind x86 in this respect.

I remember the crash caused by not tracking unmapped pages by the way. At
the time Xen was not notifying the qemu on increase_reservation, so qemu was
not refreshing its guest memory map and would crash when newly-allocated
pages were the source or detsination of I/O operations. Looks like it's
double fixed -- Xen is invalidating on both increase and decrease
reservation, and qemu-dm is able to lazily fault in new guest mappings.

>> Anyway I don't see what getting rid of the mapcache fixes.
> 
> Well, that was mostly to speed up memory lookup in the usual case, I
> don't really need it.

It's a good aim, I just think the optimisation should be done within the
context of the mapcache subsystem.

 -- Keir



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