Re: [PATCH] Cast __page_to_pfn to unsigned long in CONFIG_SPARSEMEM

Dave Hansen
2007-11-19T20:09:57Z

On Mon, 2007-11-19 at 14:52 -0500, Mathieu Desnoyers wrote:
> * Dave Hansen (haveblue@us.ibm.com) wrote:
> > On Mon, 2007-11-19 at 13:52 -0500, Mathieu Desnoyers wrote:
> > > > > So I guess the result is a pointer ? Should this be expected ?
> > > >
> > > > Nope. 'pointer - pointer' is an integer. Just solve this equation for
> > > > integer:
> > > >
> > > > 'pointer + integer = pointer'
> > > >
> > >
> > > Well, using page_to_pfn turns out to be ugly in markers (and in
> > > printks) then. Depending on the architecture, it will result in either
> > > an unsigned long (x86_64) or an unsigned int (i386), which corresponds
> > > to %lu or %u and will print a warning if we don't cast it explicitly.
> >
> > Casting the i386 one to be an unconditional 'unsigned long' shouldn't be
> > an issue. We don't generally expect pfns to fit into ints anyway.
>
> So would this make sense ?
>
> Cast __page_to_pfn to unsigned long in CONFIG_SPARSEMEM
>
> Make sure the type returned by __page_to_pfn is always unsigned long. If we
> don't cast it explicitly, it can be int on i386, but long on x86_64. This is
> especially inelegant for printks.

The only thing I might suggest doing differently is actually using the
page_to_pfn() definition itself:

memory_model.h:#define page_to_pfn __page_to_pfn

The full inline function version should do this already, and we
shouldn't have any real direct __page_to_pfn() users anyway.

-- Dave