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Date: Wed, 22 Apr 2009 09:20:40 +0900 (JST) From: KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com> To: Mel Gorman <mel@....ul.ie> Cc: kosaki.motohiro@...fujitsu.com, Linux Memory Management List <linux-mm@...ck.org>, Christoph Lameter <cl@...ux-foundation.org>, Nick Piggin <npiggin@...e.de>, Linux Kernel Mailing List <linux-kernel@...r.kernel.org>, Lin Ming <ming.m.lin@...el.com>, Zhang Yanmin <yanmin_zhang@...ux.intel.com>, Peter Zijlstra <peterz@...radead.org>, Pekka Enberg <penberg@...helsinki.fi>, Andrew Morton <akpm@...ux-foundation.org> Subject: Re: [PATCH 20/25] Do not check for compound pages during the page allocator sanity checks > A number of sanity checks are made on each page allocation and free > including that the page count is zero. page_count() checks for > compound pages and checks the count of the head page if true. However, > in these paths, we do not care if the page is compound or not as the > count of each tail page should also be zero. > > This patch makes two changes to the use of page_count() in the free path. It > converts one check of page_count() to a VM_BUG_ON() as the count should > have been unconditionally checked earlier in the free path. It also avoids > checking for compound pages. > > [mel@....ul.ie: Wrote changelog] > Signed-off-by: Nick Piggin <nickpiggin@...oo.com.au> > Reviewed-by: Christoph Lameter <cl@...ux-foundation.org> > --- > mm/page_alloc.c | 6 +++--- > 1 files changed, 3 insertions(+), 3 deletions(-) > > diff --git a/mm/page_alloc.c b/mm/page_alloc.c > index ec01d8f..376d848 100644 > --- a/mm/page_alloc.c > +++ b/mm/page_alloc.c > @@ -425,7 +425,7 @@ static inline int page_is_buddy(struct page *page, struct page *buddy, > return 0; > > if (PageBuddy(buddy) && page_order(buddy) == order) { > - BUG_ON(page_count(buddy) != 0); > + VM_BUG_ON(page_count(buddy) != 0); > return 1; > } > return 0; > Looks good. > @@ -501,7 +501,7 @@ static inline int free_pages_check(struct page *page) > { > if (unlikely(page_mapcount(page) | > (page->mapping != NULL) | > - (page_count(page) != 0) | > + (atomic_read(&page->_count) != 0) | > (page->flags & PAGE_FLAGS_CHECK_AT_FREE))) { > bad_page(page); > return 1; > @@ -646,7 +646,7 @@ static int prep_new_page(struct page *page, int order, gfp_t gfp_flags) > { > if (unlikely(page_mapcount(page) | > (page->mapping != NULL) | > - (page_count(page) != 0) | > + (atomic_read(&page->_count) != 0) | > (page->flags & PAGE_FLAGS_CHECK_AT_PREP))) { > bad_page(page); > return 1; inserting VM_BUG_ON(PageTail(page)) is better? -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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