From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx192.postini.com [74.125.245.192]) by kanga.kvack.org (Postfix) with SMTP id A3BB38D0011 for ; Thu, 6 Dec 2012 16:09:44 -0500 (EST) Message-ID: <50C10997.8090801@codeaurora.org> Date: Thu, 06 Dec 2012 13:09:43 -0800 From: Laura Abbott MIME-Version: 1.0 Subject: Re: [PATCH v2] mm: Use aligned zone start for pfn_to_bitidx calculation References: <1354824324-21993-1-git-send-email-lauraa@codeaurora.org> In-Reply-To: <1354824324-21993-1-git-send-email-lauraa@codeaurora.org> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Laura Abbott Cc: Mel Gorman , linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-arm-msm@vger.kernel.org On 12/6/2012 12:05 PM, Laura Abbott wrote: > 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..2e06abd 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->start_pfn, pageblock_nr_pages); > return (pfn >> pageblock_order) * NR_PAGEBLOCK_BITS; > #endif /* CONFIG_SPARSEMEM */ > } > Sorry for the spam, please ignore this one. This has a typo. Third times the charm. -- Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, hosted by The Linux Foundation -- 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