On Mon, Aug 23, 2010 at 07:56:40AM -0500, Christoph Lameter wrote: > On Mon, 23 Aug 2010, Mel Gorman wrote: > > > This patch introduces zone_nr_free_pages() to take a slightly more accurate > > estimate of NR_FREE_PAGES while kswapd is awake. The estimate is not perfect > > and may result in cache line bounces but is expected to be lighter than the > > IPI calls necessary to continually drain the per-cpu counters while kswapd > > is awake. > > 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. > Also would it be possible to add the summation function to vmstat? It may > be useful elsewhere. > > A new function like > > zone_page_state_snapshot() > > or so? > We could if there is another counter that results in bad system behaviour due to counter drift. As NR_FREE_PAGES seemed to be the only one, zone_nr_free_pages() seemed adequate. If such a helper did exist, zone_nr_free_pages() would be a simple wrapper around it. The indirection didn't seem necessary at this point though. -- 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>