On Mon, Aug 23, 2010 at 08:41:56AM -0500, Christoph Lameter wrote: > On Mon, 23 Aug 2010, Mel Gorman wrote: > > > > The delta of the counters could also be reduced to increase accuracy. > > > See refresh_zone_stat_thresholds(). > > True, but I thought that would introduce a constant performance penalty > > for a corner case which I didn't like. > > Sure, an increased frequency of updates would increase the chance of > bouncing cachelines. But the bouncing cacheline scenario for the vm > counters was tuned for applications that continually allocate pages in > parallel. > > When the vm gets into a state where continual reclaim is necessary then > the counters are not that frequently updated. If the machine is already > slowing down due to reclaim then the vm can likely affort more frequent > counter updates. > Ok, but is that better than this patch? Decreasing the size of the window by reducing the threshold still leaves a window. There is still a small amount of drift by summing up all the deltas but you get a much more accurate count at the point of time it was important to know. -- 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>