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Message-ID: <50C10997.8090801@codeaurora.org> Date: Thu, 06 Dec 2012 13:09:43 -0800 From: Laura Abbott <lauraa@...eaurora.org> To: Laura Abbott <lauraa@...eaurora.org> CC: Mel Gorman <mgorman@...e.de>, linux-mm@...ck.org, linux-kernel@...r.kernel.org, linux-arm-msm@...r.kernel.org Subject: Re: [PATCH v2] mm: Use aligned zone start for pfn_to_bitidx calculation 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 <lauraa@...eaurora.org> > --- > 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 from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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