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?
rday
--
========================================================================
Robert P. J. Day
Linux Consulting, Training and Annoying Kernel Pedantry
Waterloo, Ontario, CANADA
http://fsdev.net/wiki/index.php?title=Main_Page
========================================================================
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