The patch titled
Subject: mm: use aligned zone start for pfn_to_bitidx calculation
has been added to the -mm tree. Its filename is
mm-use-aligned-zone-start-for-pfn_to_bitidx-calculation.patch
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------------------------------------------------------
From: Laura Abbott <lauraa@xxxxxxxxxxxxxx>
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.
Signed-off-by: Laura Abbott <lauraa@xxxxxxxxxxxxxx>
Acked-by: Mel Gorman <mgorman@xxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/page_alloc.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff -puN mm/page_alloc.c~mm-use-aligned-zone-start-for-pfn_to_bitidx-calculation mm/page_alloc.c
--- a/mm/page_alloc.c~mm-use-aligned-zone-start-for-pfn_to_bitidx-calculation
+++ a/mm/page_alloc.c
@@ -5604,7 +5604,7 @@ static inline int pfn_to_bitidx(struct z
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 */
}
_
Patches currently in -mm which might be from lauraa@xxxxxxxxxxxxxx are
mm-use-aligned-zone-start-for-pfn_to_bitidx-calculation.patch
debugging-keep-track-of-page-owners.patch
debugging-keep-track-of-page-owners-fix.patch
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