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SubjectRe: [PATCH 1/1] handle initialising compound pages at orders greater than MAX_ORDER
On Thu,  2 Oct 2008 17:19:56 +0100
Andy Whitcroft <apw@shadowen.org> wrote:

> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -268,13 +268,14 @@ void prep_compound_page(struct page *page, unsigned long order)
> {
> int i;
> int nr_pages = 1 << order;
> + struct page *p = page + 1;
>
> set_compound_page_dtor(page, free_compound_page);
> set_compound_order(page, order);
> __SetPageHead(page);
> - for (i = 1; i < nr_pages; i++) {
> - struct page *p = page + i;
> -
> + for (i = 1; i < nr_pages; i++, p++) {
> + if (unlikely((i & (MAX_ORDER_NR_PAGES - 1)) == 0))
> + p = pfn_to_page(page_to_pfn(page) + i);
> __SetPageTail(p);
> p->first_page = page;
> }

gad. Wouldn't it be clearer to do

for (i = 1; i < nr_pages; i++) {
struct page *p = pfn_to_page(i);
__SetPageTail(p);
p->first_page = page;
}
Oh well, I guess we can go with the obfuscated, uncommented version for
now :(

This patch applies to 2.6.26 (and possibly earlier) but I don't think
those kernels can trigger the bug?



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