From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail143.messagelabs.com (mail143.messagelabs.com [216.82.254.35]) by kanga.kvack.org (Postfix) with ESMTP id 369BA6B00AA for ; Wed, 22 Apr 2009 06:09:55 -0400 (EDT) Date: Wed, 22 Apr 2009 11:09:58 +0100 From: Mel Gorman Subject: Re: [PATCH 20/25] Do not check for compound pages during the page allocator sanity checks Message-ID: <20090422100958.GB10380@csn.ul.ie> References: <1240266011-11140-1-git-send-email-mel@csn.ul.ie> <1240266011-11140-21-git-send-email-mel@csn.ul.ie> <20090422091456.626E.A69D9226@jp.fujitsu.com> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-15 Content-Disposition: inline In-Reply-To: <20090422091456.626E.A69D9226@jp.fujitsu.com> Sender: owner-linux-mm@kvack.org To: KOSAKI Motohiro Cc: Linux Memory Management List , Christoph Lameter , Nick Piggin , Linux Kernel Mailing List , Lin Ming , Zhang Yanmin , Peter Zijlstra , Pekka Enberg , Andrew Morton List-ID: On Wed, Apr 22, 2009 at 09:20:40AM +0900, KOSAKI Motohiro wrote: > > 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@csn.ul.ie: Wrote changelog] > > Signed-off-by: Nick Piggin > > Reviewed-by: Christoph Lameter > > --- > > 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? > We already go one further with #define PAGE_FLAGS_CHECK_AT_PREP ((1 << NR_PAGEFLAGS) - 1) ... if (.... | (page->flags & PAGE_FLAGS_CHECK_AT_PREP)) bad_page(page); PG_tail is in PAGE_FLAGS_CHECK_AT_PREP so we're already checking for it and calling bad_page() if set. -- Mel Gorman Part-time Phd Student Linux Technology Center University of Limerick IBM Dublin Software Lab -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org