lkml.org 
[lkml]   [2008]   [Oct]   [3]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    From
    SubjectRe: [PATCH 1/1] handle initialising compound pages at orders greater than MAX_ORDER
    Date
    On Friday 03 October 2008 07:30, Andrew Morton wrote:
    > 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?

    I think the problem is that pfn_to_page isn't always trivial. I would
    prefer to have seen a new function for hugetlb to use, and keep the
    branch-less version for the page allocator itself.


    \
     
     \ /
      Last update: 2008-10-03 08:45    [W:0.026 / U:1.016 seconds]
    ©2003-2016 Jasper Spaans. hosted at Digital OceanAdvertise on this site