On Tue, Mar 09, 2010 at 11:11:55AM -0600, Christoph Lameter wrote: > On Tue, 9 Mar 2010, Mel Gorman wrote: > > > Until it's timeout at least. It's still better than the current > > situation of sleeping on congestion. > > Congestion may clear if memory becomes available in other zones. > I understand that. > > The ideal would be waiting on a per-node basis. I'm just not liking having > > to look up the node structure when freeing a patch of pages and making a > > cache line in there unnecessarily hot. > > The node structure (pgdat) contains the zone structures. If you know the > type of zone then you can calculate the pgdat address. > I know you can lookup the pgdat from the zone structure. The concern is that the suggestion requires adding fields to the node structure that then become hot in the free_page path when the per-cpu lists are being drained. This patch also adds a hot cache line to the zone but at least it can be eliminated by using zone->flags. The same optimisation does not apply to working on a per-node basis. Adding such a hot line is a big minus and the gain is that processes may wake up slightly faster when under memory pressure. It's not a good trade-off. > > > But then an overallocated node may stall processes. If that node is full > > > of unreclaimable memory then the process may never wake up? > > > > Processes wake after a timeout. > > Ok that limits it but still we may be waiting for no reason. > -- Mel Gorman Part-time Phd Student Linux Technology Center University of Limerick IBM Dublin Software Lab -- 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/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>