From: Laura Abbott Date: Fri, 11 Jan 2013 22:31:51 +0000 (-0800) Subject: mm: use aligned zone start for pfn_to_bitidx calculation X-Git-Tag: v3.7.3~206 X-Git-Url: https://git.karo-electronics.de/?a=commitdiff_plain;h=6f72e73ab0fb89eb51afd9a6dbb2ff339541b3c1;p=karo-tx-linux.git mm: use aligned zone start for pfn_to_bitidx calculation 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: Greg Kroah-Hartman --- diff --git a/mm/page_alloc.c b/mm/page_alloc.c index 7e208f0ad68c..fe04c342f0d4 100644 --- a/mm/page_alloc.c +++ b/mm/page_alloc.c @@ -5506,7 +5506,7 @@ 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 */ }