On Thu, Dec 06, 2012 at 01:11:41PM -0800, Laura Abbott wrote:

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 <redacted>

Acked-by: Mel Gorman <mgorman@suse.de>

It's merge window at the moment so it's in danger of getting lost. What
I suggest you do is do is resend to Andrew with the same people cc'd
post-merge window so it'll be picked up in mmotm for the next cycle.

Thanks.

-- 
Mel Gorman
SUSE Labs

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