path: root/mm
diff options
authorLaura Abbott <lauraa@codeaurora.org>2013-01-11 14:31:51 -0800
committerLinus Torvalds <torvalds@linux-foundation.org>2013-01-11 14:54:55 -0800
commitc060f943d0929f3e429c5d9522290584f6281d6e (patch)
treeccbc72cee7202d8591aa9c5fa55dcc465bbd2a35 /mm
parent6d92d4f6a74766cc885b18218268e0c47fbca399 (diff)
mm: use aligned zone start for pfn_to_bitidx calculation
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 <lauraa@codeaurora.org> Acked-by: Mel Gorman <mgorman@suse.de> Cc: <stable@vger.kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'mm')
1 files changed, 1 insertions, 1 deletions
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index bc6cc0e913b..c957805a7f0 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -5604,7 +5604,7 @@ static inline int pfn_to_bitidx(struct zone *zone, unsigned long pfn)
return (pfn >> pageblock_order) * NR_PAGEBLOCK_BITS;
- pfn = pfn - zone->zone_start_pfn;
+ pfn = pfn - round_down(zone->zone_start_pfn, pageblock_nr_pages);
return (pfn >> pageblock_order) * NR_PAGEBLOCK_BITS;