Messages in this thread | | | Date | Tue, 9 Mar 2010 17:30:03 +0000 | From | Mel Gorman <> | Subject | Re: [PATCH 1/3] page-allocator: Under memory pressure, wait on pressure to relieve instead of congestion |
| |
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
| |