Re: Extend clear_page by an order parameter

[Andrew Morton <akpm@osdl.org>]

Christoph Lameter <clameter@sgi.com> wrote:
>
> The zeroing of a page of a arbitrary order in page_alloc.c and in hugetlb.c may benefit from a
>  clear_page that is capable of zeroing multiple pages at once (and scrubd
>  too but that is now an independent patch). The following patch extends
>  clear_page with a second parameter specifying the order of the page to be zeroed to allow an
>  efficient zeroing of pages. Hope I caught everything....
> 

Sorry, I take it back.  As Paul says:

: Wouldn't it be nicer to call the version that takes the order
: parameter "clear_pages" and then define clear_page(p) as
: clear_pages(p, 0) ?

It would make the patch considerably smaller, and our naming is all over
the place anyway...

>  -static inline void prep_zero_page(struct page *page, int order, int gfp_flags)
>  +void prep_zero_page(struct page *page, unsigned int order, unsigned int gfp_flags)
>   {
>   	int i;
> 
>   	BUG_ON((gfp_flags & (__GFP_WAIT | __GFP_HIGHMEM)) = __GFP_HIGHMEM);
>  +	if (!PageHighMem(page)) {
>  +		clear_page(page_address(page), order);
>  +		return;
>  +	}
>  +
>   	for(i = 0; i < (1 << order); i++)
>   		clear_highpage(page + i);
>   }

I'd have thought that we'd want to make the new clear_pages() handle
highmem pages too, if only from a regularity POV.  x86 hugetlbpages could
use it then, if someone thinks up a fast page-clearer.