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

[Paul Brook]

> On Wed, Mar 17, 2010 at 03:05:57PM +0000, Paul Brook wrote:
> > > +       if (size >= PREFERRED_RAM_ALIGN)
> > > +               new_block->host = qemu_memalign(PREFERRED_RAM_ALIGN,
> > > size);
> >
> > Is this deliberately bigger-than rather than multiple-of?
> > Having the size not be a multiple of alignment seems somewhat strange,
> > it's always going to be wrong at one end...
> 
> 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.

> The guest physical address that the host
> retval corresponds to, has to be aligned with PREFERRED_RAM_ALIGN for
> NPT/EPT to work. I don't think it's a big concern right now.
 
If you allocating chinks that are multiples of the relevant page size, then I 
don't think you can expect anything particularly sensible to happen.

Paul