From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755113Ab3AXDgb (ORCPT ); Wed, 23 Jan 2013 22:36:31 -0500 Received: from youngberry.canonical.com ([91.189.89.112]:44376 "EHLO youngberry.canonical.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754751Ab3AXDbB (ORCPT ); Wed, 23 Jan 2013 22:31:01 -0500 From: Herton Ronaldo Krzesinski To: linux-kernel@vger.kernel.org, stable@vger.kernel.org, kernel-team@lists.ubuntu.com Cc: Laura Abbott , Andrew Morton , Linus Torvalds , Herton Ronaldo Krzesinski Subject: [PATCH 54/74] mm: use aligned zone start for pfn_to_bitidx calculation Date: Thu, 24 Jan 2013 01:27:06 -0200 Message-Id: <1358998046-613-55-git-send-email-herton.krzesinski@canonical.com> X-Mailer: git-send-email 1.7.9.5 In-Reply-To: <1358998046-613-1-git-send-email-herton.krzesinski@canonical.com> References: <1358998046-613-1-git-send-email-herton.krzesinski@canonical.com> X-Extended-Stable: 3.5 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 3.5.7.4 -stable review patch. If anyone has any objections, please let me know. ------------------ From: Laura Abbott commit c060f943d0929f3e429c5d9522290584f6281d6e upstream. The current calculation in pfn_to_bitidx assumes that (pfn - zone->zone_start_pfn) >> pageblock_order will return the same bit for all pfn in a pageblock. If zone_start_pfn is not aligned to pageblock_nr_pages, this may not always be correct. Consider the following with pageblock order = 10, zone start 2MB: pfn | pfn - zone start | (pfn - zone start) >> page block order ---------------------------------------------------------------- 0x26000 | 0x25e00 | 0x97 0x26100 | 0x25f00 | 0x97 0x26200 | 0x26000 | 0x98 0x26300 | 0x26100 | 0x98 This means that calling {get,set}_pageblock_migratetype on a single page will not set the migratetype for the full block. Fix this by rounding down zone_start_pfn when doing the bitidx calculation. For our use case, the effects of this bug were mostly tied to the fact that CMA allocations would either take a long time or fail to happen. Depending on the driver using CMA, this could result in anything from visual glitches to application failures. Signed-off-by: Laura Abbott Acked-by: Mel Gorman Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds Signed-off-by: Herton Ronaldo Krzesinski --- mm/page_alloc.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/mm/page_alloc.c b/mm/page_alloc.c index 9bd526c..007bf3b 100644 --- a/mm/page_alloc.c +++ b/mm/page_alloc.c @@ -5405,7 +5405,7 @@ static inline int pfn_to_bitidx(struct zone *zone, unsigned long pfn) pfn &= (PAGES_PER_SECTION-1); return (pfn >> pageblock_order) * NR_PAGEBLOCK_BITS; #else - pfn = pfn - zone->zone_start_pfn; + pfn = pfn - round_down(zone->zone_start_pfn, pageblock_nr_pages); return (pfn >> pageblock_order) * NR_PAGEBLOCK_BITS; #endif /* CONFIG_SPARSEMEM */ } -- 1.7.9.5