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/
