Messages in this thread | | | Date | Thu, 06 Dec 2012 13:09:43 -0800 | From | Laura Abbott <> | Subject | Re: [PATCH v2] mm: Use aligned zone start for pfn_to_bitidx calculation |
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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@codeaurora.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.
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