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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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