Re: [PATCH] Handle vma regions with no backing page

[Muli Ben-Yehuda <muli@il.ibm.com>]

On Wed, Jun 04, 2008 at 06:09:24PM +0300, Ben-Ami Yassour1 wrote:

> > > We noticed that pfn_valid does not always works as expected by
> > > this patch to indicate that a pfn has a backing page.  We have
> > > seen a case where CONFIG_NUMA was not set and then where
> > > pfn_valid returned 1 for an mmio pfn.  We then changed the
> > > config file with CONFIG_NUMA set and it worked fine as expected
> > > (since a different implementation of pfn_valid was used).
> > >
> > > How should we overcome this issue?
> > 
> > There's a page_is_ram() too, but that's the e820 map check and it
> > means it's RAM not that there's a page backing store. Certainly if
> > it's not ram we should go ahead with just the pfn but it'd be a
> > workaround.
> > 
> > I really think it'd be better off to fix pfn_valid to work for
> > NUMA.
> 
> It does work for NUMA, it does not work without the NUMA option.

Andrea, how would you suggest to fix pfn_valid for the CONFIG_NUMA
disabled case?

Cheers,
Muli