From mboxrd@z Thu Jan 1 00:00:00 1970 From: Laura Abbott Subject: [PATCH v3] mm: Use aligned zone start for pfn_to_bitidx calculation Date: Thu, 6 Dec 2012 13:11:41 -0800 Message-ID: <1354828301-27849-1-git-send-email-lauraa@codeaurora.org> Return-path: Received: from wolverine01.qualcomm.com ([199.106.114.254]:49554 "EHLO wolverine01.qualcomm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754285Ab2LFVLt (ORCPT ); Thu, 6 Dec 2012 16:11:49 -0500 Sender: linux-arm-msm-owner@vger.kernel.org List-Id: linux-arm-msm@vger.kernel.org To: Mel Gorman , linux-mm@kvack.org Cc: linux-kernel@vger.kernel.org, linux-arm-msm@vger.kernel.org, Laura Abbott 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. Signed-off-by: Laura Abbott --- mm/page_alloc.c | 2 +- 1 files changed, 1 insertions(+), 1 deletions(-) diff --git a/mm/page_alloc.c b/mm/page_alloc.c index 92dd060..b6a2510 100644 --- a/mm/page_alloc.c +++ b/mm/page_alloc.c @@ -5422,7 +5422,7 @@ 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 */ } -- The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum, hosted by The Linux Foundation