commit: c060f943d0929f3e429c5d9522290584f6281d6e
From: Laura Abbott <[email protected]>
Date: Fri, 11 Jan 2013 14:31:51 -0800
Subject: 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 <[email protected]>
Acked-by: Mel Gorman <[email protected]>
Cc: <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>
---
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 bc6cc0e..c957805 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)
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 */
}
--
1.7.3.4
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