Re: [patch 2/6] mm: introduce pte_special pte bit

[Sam Ravnborg <sam@ravnborg.org>]

On Fri, Jan 18, 2008 at 08:41:22AM -0800, Linus Torvalds wrote:
> 
> 
> On Fri, 18 Jan 2008, npiggin@suse.de wrote:
> >   */
> > +#ifdef __HAVE_ARCH_PTE_SPECIAL
> > +# define HAVE_PTE_SPECIAL 1
> > +#else
> > +# define HAVE_PTE_SPECIAL 0
> > +#endif
> >  struct page *vm_normal_page(struct vm_area_struct *vma, unsigned long addr, pte_t pte)
> >  {
> > -	unsigned long pfn = pte_pfn(pte);
> > +	unsigned long pfn;
> > +
> > +	if (HAVE_PTE_SPECIAL) {
> 
> I really don't think this is *any* different from "#ifdefs in code".

One fundamental difference is that with the above syntax we always
compile both versions of the code - so we do not end up with one
version that builds and another version that dont.

This has always striked me as a good reason to do the above and
I think it is busybox that does so with success.

	Sam

--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@kvack.org.  For more info on Linux MM,
see: http://www.linux-mm.org/ .
Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>