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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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