Re: why does the macro "ZERO_PAGE" take an argument?

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

 



On 6/7/07, Robert P. J. Day <[email protected]> wrote:
On Thu, 7 Jun 2007, Nick Piggin wrote:

> Robert P. J. Day wrote:
> >   probably making a fool of myself here, but what is the purpose of
> > that single argument to the macro "ZERO_PAGE"?
> >
> > $ grep -r "define ZERO_PAGE" include
> > include/asm-frv/pgtable.h:#define ZERO_PAGE(vaddr)      ({ BUG(); NULL; })
> > include/asm-frv/pgtable.h:#define ZERO_PAGE(vaddr)
> > virt_to_page(empty_zero_page)
> > include/asm-v850/pgtable.h:#define ZERO_PAGE(vaddr)     ((void *)0x87654321)
> > include/asm-mips/pgtable.h:#define ZERO_PAGE(vaddr) \
> > include/asm-blackfin/pgtable.h:#define ZERO_PAGE(vaddr) (virt_to_page(0))
> > include/asm-parisc/pgtable.h:#define ZERO_PAGE(vaddr)
> > (virt_to_page(empty_zero_page))
> > include/asm-alpha/pgtable.h:#define ZERO_PAGE(vaddr)
> > (virt_to_page(ZERO_PGE))
> > ...
> >
> >   AFAICT, there are no definitions of that macro that actually use
> > that argument.  is that some kind of historical cruft?
>
> MIPS?

argh. that would be the *one* definition whose output got chopped
because of line continuation, and it would be only one that actually
uses the argument:

#define ZERO_PAGE(vaddr) \
        (virt_to_page((void *)(empty_zero_page + (((unsigned long)(vaddr)) & zero_page_mask))))


but it still leaves the question -- if ZERO_PAGE is meant to represent
a single, global shared page that is always zero, why would it *ever*
need to take an argument?  and what's so special about MIPS that it
differs from all the rest?

The comment above empty_zero_page and zero_page_mask
declarations at arch/mips/mm/init.c:508 sheds light on this ...
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to [email protected]
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/

[Index of Archives]     [Kernel Newbies]     [Netfilter]     [Bugtraq]     [Photo]     [Stuff]     [Gimp]     [Yosemite News]     [MIPS Linux]     [ARM Linux]     [Linux Security]     [Linux RAID]     [Video 4 Linux]     [Linux for the blind]     [Linux Resources]
  Powered by Linux