Re: [Qemu-devel] [PATCH QEMU] Transparent Hugepage Support #3

[Paul Brook]

> On Wed, Mar 17, 2010 at 03:52:15PM +0000, Paul Brook wrote:
> > > > > Size not multiple I think is legitimate, the below-4G chunk isn't
> > > > > required to end 2M aligned, all it matters is that the above-4G
> > > > > then starts aligned. In short one thing to add in the future as
> > > > > parameter to qemu_ram_alloc is the physical address that the host
> > > > > virtual address corresponds to.
> > > >
> > > > In general you don't know this at allocation time.
> > >
> > > Caller knows it, it's not like the caller is outside of qemu, it's not
> > > some library. We know this is enough with the caller that there is now.
> >
> > No we don't.  As discussed previously, there are machines where the
> > physical location of RAM is configurable at runtime.  In fact it's common
> > for the ram to be completely absent at reset.
> 
> This is why PREFERRED_RAM_ALIGN is only defined for __x86_64__. I'm
> not talking about other archs that may never support transparent
> hugepages in the kernel because of other architectural constrains that
> may prevent to map hugepages mixed with regular pages in the same vma.

__x86__64 only tells you about the host. I'm talking about the guest machine.

Paul