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    SubjectRe: [patch 1/4] mm: page_alloc: remove order assumption from __free_pages_bootmem()
    On Tue, 13 Dec 2011 14:58:28 +0100
    Johannes Weiner <hannes@cmpxchg.org> wrote:

    > Even though bootmem passes an order with the page to be freed,
    > __free_pages_bootmem() assumes that 1 << order is always BITS_PER_LONG
    > if non-zero. While this happens to be true, it's not really robust.
    > Remove that assumption and use 1 << order instead.
    >
    > Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
    > ---
    > mm/page_alloc.c | 7 ++++---
    > 1 files changed, 4 insertions(+), 3 deletions(-)
    >
    > diff --git a/mm/page_alloc.c b/mm/page_alloc.c
    > index 2b8ba3a..4d5e91c 100644
    > --- a/mm/page_alloc.c
    > +++ b/mm/page_alloc.c
    > @@ -703,13 +703,14 @@ void __meminit __free_pages_bootmem(struct page *page, unsigned int order)
    > set_page_refcounted(page);
    > __free_page(page);
    > } else {
    > - int loop;
    > + unsigned int nr_pages = 1 << order;
    > + unsigned int loop;
    >
    > prefetchw(page);
    > - for (loop = 0; loop < BITS_PER_LONG; loop++) {
    > + for (loop = 0; loop < nr_pages; loop++) {
    > struct page *p = &page[loop];
    >
    > - if (loop + 1 < BITS_PER_LONG)
    > + if (loop + 1 < nr_pages)
    > prefetchw(p + 1);
    > __ClearPageReserved(p);
    > set_page_count(p, 0);

    Tejun has recently secretly snuck the below (rather old) patch into
    linux-next's page_alloc.c. I think I got everything fixed up right -
    please check.

    commit 53348f27168534561c0c814843bbf181314374f4
    Author: Tejun Heo <tj@kernel.org>
    AuthorDate: Tue Jul 12 09:58:06 2011 +0200
    Commit: H. Peter Anvin <hpa@linux.intel.com>
    CommitDate: Wed Jul 13 16:35:56 2011 -0700

    bootmem: Fix __free_pages_bootmem() to use @order properly

    a226f6c899 (FRV: Clean up bootmem allocator's page freeing algorithm)
    separated out __free_pages_bootmem() from free_all_bootmem_core().
    __free_pages_bootmem() takes @order argument but it assumes @order is
    either 0 or ilog2(BITS_PER_LONG). Note that all the current users
    match that assumption and this doesn't cause actual problems.

    Fix it by using 1 << order instead of BITS_PER_LONG.

    Signed-off-by: Tejun Heo <tj@kernel.org>
    Link: http://lkml.kernel.org/r/1310457490-3356-3-git-send-email-tj@kernel.org
    Cc: David Howells <dhowells@redhat.com>
    Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>

    diff --git a/mm/page_alloc.c b/mm/page_alloc.c
    index 9119faa..b6da6ed 100644
    --- a/mm/page_alloc.c
    +++ b/mm/page_alloc.c
    @@ -705,10 +705,10 @@ void __meminit __free_pages_bootmem(struct page *page, unsigned int order)
    int loop;

    prefetchw(page);
    - for (loop = 0; loop < BITS_PER_LONG; loop++) {
    + for (loop = 0; loop < (1 << order); loop++) {
    struct page *p = &page[loop];

    - if (loop + 1 < BITS_PER_LONG)
    + if (loop + 1 < (1 << order))
    prefetchw(p + 1);
    __ClearPageReserved(p);
    set_page_count(p, 0);


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