On Tue, Mar 09, 2010 at 10:09:11AM -0600, Christoph Lameter wrote: > On Tue, 9 Mar 2010, Christian Ehrhardt wrote: > > > > What happens if memory becomes available in another zone? Lets say we are > > > waiting on HIGHMEM and memory in ZONE_NORMAL becomes available? > > > > Do you mean the same as Nick asked or another aspect of it? > > citation: > > "I mean the other way around. If that zone's watermarks are not met, then why > > shouldn't it be woken up by other zones reaching their watermarks." > > Just saw that exchange. Yes it is similar. Mel only thought about NUMA > but the situation can also occur in !NUMA because multiple zones do not > require NUMA. > True, although rare. Elsewhere I suggested that the wait could be on a per-node basis instead of per-zone. My main concern there would be adding a new hot cache line in the page free path or an unfortunate mix of zone and node logic. I'm not fully convinced it's worth it but will check it out. > If a process goes to sleep on an allocation that has a preferred zone of > HIGHMEM then other processors may free up memory in ZONE_DMA and > ZONE_NORMAL and therefore memory may become available but the process will > continue to sleep. > Until it's timeout at least. It's still better than the current situation of sleeping on congestion. 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 wait structure needs to be placed in the pgdat structure to make it > node specific. > > 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. -- 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>