On Tue, Feb 22, 2011 at 03:42:00PM +0100, Andrea Arcangeli wrote: > <SNIP> > > I'm also intrigued by reducing this from 2 to 1: > > /* Make sure at least 2 hugepages are free for MIGRATE_RESERVE */ > recommended_min = pageblock_nr_pages * nr_zones * 2; > > Do we really need 2 pages instead of just 1 here to provide the > guarantee? For workloads that cause a lot of fragmentation - yes. Simplistically with 1, the trace event mm_page_alloc_extfrag will trigger more frequently and it's more likely to be severe. The problem is that if it's not "* 2", there is a very low probability that there will pages free in a suitable pageblock and "mixing" occurs. It can take a very long time for allocation success rates to go down but it happens eventually. -- Mel Gorman SUSE Labs -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxxx 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>