On Sat, 5 Jan 2013 11:28:31 -0800
Laura Abbott <lauraa@xxxxxxxxxxxxxx> 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.
What are the user-visible effects of this bug?