From 6babc32c41e3642d875372cb6afbd9ade7a9f311 Mon Sep 17 00:00:00 2001 From: Andy Whitcroft Date: Thu, 2 Oct 2008 14:50:18 -0700 Subject: [PATCH] mm: handle initialising compound pages at orders greater than MAX_ORDER 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. Credit to Mel Gorman for spotting the issue. Signed-off-by: Andy Whitcroft Cc: Mel Gorman Cc: Jon Tollefson Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- mm/page_alloc.c | 13 ++++++++----- 1 file changed, 8 insertions(+), 5 deletions(-) diff --git a/mm/page_alloc.c b/mm/page_alloc.c index e293c58bea58..27b8681139fd 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))) -- 2.30.2