Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754755AbYJBQUL (ORCPT ); Thu, 2 Oct 2008 12:20:11 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1753812AbYJBQT7 (ORCPT ); Thu, 2 Oct 2008 12:19:59 -0400 Received: from tallyho.bytemark.co.uk ([80.68.81.166]:40131 "EHLO tallyho.bytemark.co.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753716AbYJBQT6 (ORCPT ); Thu, 2 Oct 2008 12:19:58 -0400 From: Andy Whitcroft To: Andrew Morton Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, Jon Tollefson , Mel Gorman , Andy Whitcroft Subject: [PATCH 1/1] handle initialising compound pages at orders greater than MAX_ORDER Date: Thu, 2 Oct 2008 17:19:56 +0100 Message-Id: <1222964396-25031-1-git-send-email-apw@shadowen.org> X-Mailer: git-send-email 1.6.0.1.451.gc8d31 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2710 Lines: 74 When we initialise a compound page we initialise the page flags and head page pointer for all base pages spanned by that page. When we initialise a gigantic page (a page of order greater than or equal to MAX_ORDER) we have to initialise more than MAX_ORDER_NR_PAGES pages. Currently we assume that all elements of the mem_map in this page are contigious in memory. However this is only guarenteed out to MAX_ORDER_NR_PAGES pages, and with SPARSEMEM enabled they will not be contigious. This leads us to walk off the end of the first section and scribble on everything which follows, BAD. When we reach a MAX_ORDER_NR_PAGES boundary we much locate the next section of the mem_map. As gigantic pages can only be maximally aligned we know this will occur at exact multiple of MAX_ORDER_NR_PAGES pages from the start of the page. This is a bug fix for the gigantic page support in hugetlbfs, please consider for merging before 2.6.27. Credit to Mel Gorman for spotting the issue. Signed-off-by: Andy Whitcroft --- mm/page_alloc.c | 13 ++++++++----- 1 files changed, 8 insertions(+), 5 deletions(-) diff --git a/mm/page_alloc.c b/mm/page_alloc.c index e293c58..27b8681 100644 --- 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; } @@ -284,6 +285,7 @@ static void destroy_compound_page(struct page *page, unsigned long order) { int i; int nr_pages = 1 << order; + struct page *p = page + 1; if (unlikely(compound_order(page) != order)) bad_page(page); @@ -291,8 +293,9 @@ static void destroy_compound_page(struct page *page, unsigned long order) if (unlikely(!PageHead(page))) bad_page(page); __ClearPageHead(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); if (unlikely(!PageTail(p) | (p->first_page != page))) -- 1.6.0.1.451.gc8d31 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/