On Mon, Aug 23, 2010 at 07:45:25AM -0500, Christoph Lameter wrote: > On Mon, 23 Aug 2010, Mel Gorman wrote: > > > Internal IBM test teams beta testing distribution kernels have reported > > problems on machines with a large number of CPUs whereby page allocator > > failure messages show huge differences between the nr_free_pages vmstat > > counter and what is available on the buddy lists. In an extreme example, > > nr_free_pages was above the min watermark but zero pages were on the buddy > > lists allowing the system to potentially livelock unable to make forward > > progress unless an allocation succeeds. There is no reason why the problems > > would not affect mainline so the following series mitigates the problems > > in the page allocator related to to per-cpu counter drift and lists. > > The maximum time for which the livelock can exists is the vm stat > interval. By default the counters are brought up to date at least once per > second or if a certain delta was violated. Drifts are controlled by the > delta configuration. > While there is a maximum time (2 seconds I think) the drift can exist in, a machine under enough pressure can make a mess of the watermarks during that time. If it wasn't the case, these livelocks with 0 pages free wouldn't be happening. -- 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>