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. The correct
fix is to round down zone_start_pfn for the bit index calculation.
Rather than do this calculation everytime, store this precalcualted
algined start in the zone structure to allow the actual start_pfn to
be used elsewhere.
Change-Id: I13e2f53f50db294f38ec86138c17c6fe29f0ee82
Signed-off-by: Laura Abbott <lauraa@xxxxxxxxxxxxxx>
---
include/linux/mmzone.h | 6 ++++++
mm/page_alloc.c | 4 +++-
2 files changed, 9 insertions(+), 1 deletions(-)
diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
index 08f74e6..0a5471b 100644
--- a/include/linux/mmzone.h
+++ b/include/linux/mmzone.h
@@ -467,6 +467,12 @@ struct zone {
struct pglist_data *zone_pgdat;
/* zone_start_pfn == zone_start_paddr >> PAGE_SHIFT */
unsigned long zone_start_pfn;
+ /*
+ * the starting pfn of the zone may not be aligned to the pageblock
+ * size which can throw off calculation of the pageblock flags.
+ * This is the precomputed aligned start of the zone
+ */
+ unsigned long aligned_start_pfn;
/*
* zone_start_pfn, spanned_pages and present_pages are all
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index c3142e8..d78e1d6 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -3968,6 +3968,8 @@ __meminit int init_currently_empty_zone(struct zone *zone,
pgdat->nr_zones = zone_idx(zone) + 1;
zone->zone_start_pfn = zone_start_pfn;
+ zone->aligned_start_pfn = round_down(zone_start_pfn,
+ pageblock_nr_pages);
mminit_dprintk(MMINIT_TRACE, "memmap_init",
"Initialising map node %d zone %lu pfns %lu -> %lu\n",
@@ -5424,7 +5426,7 @@ 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 - zone->aligned_start_pfn;
return (pfn >> pageblock_order) * NR_PAGEBLOCK_BITS;
#endif /* CONFIG_SPARSEMEM */
}
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