On Tue, 31 Jan 2012 16:35:28 +0000 Mel Gorman <mgorman@xxxxxxx> wrote: > When isolating for migration, migration starts at the start of a zone > which is not necessarily pageblock aligned. Further, it stops isolating > when COMPACT_CLUSTER_MAX pages are isolated so migrate_pfn is generally > not aligned. > > The problem is that pfn_valid is only called on the first PFN being > checked. Lets say we have a case like this > > H = MAX_ORDER_NR_PAGES boundary > | = pageblock boundary > m = cc->migrate_pfn > f = cc->free_pfn > o = memory hole > > H------|------H------|----m-Hoooooo|ooooooH-f----|------H > > The migrate_pfn is just below a memory hole and the free scanner is > beyond the hole. When isolate_migratepages started, it scans from > migrate_pfn to migrate_pfn+pageblock_nr_pages which is now in a memory > hole. It checks pfn_valid() on the first PFN but then scans into the > hole where there are not necessarily valid struct pages. > > This patch ensures that isolate_migratepages calls pfn_valid when > necessary. > > Reported-and-tested-by: Herbert van den Bergh <herbert.van.den.bergh@xxxxxxxxxx> > Signed-off-by: Mel Gorman <mgorman@xxxxxxx> > Acked-by: Michal Nazarewicz <mina86@xxxxxxxxxx> The changelog forgot to describe the user-visible effects of the bug. > Cc: stable@xxxxxxxxxx So he (and others) will be confused. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>