On Mon, 16 Aug 2010 10:42:12 +0100 Mel Gorman <mel@xxxxxxxxx> wrote: > Ordinarily watermark checks are made based on the vmstat NR_FREE_PAGES as > it is cheaper than scanning a number of lists. To avoid synchronization > overhead, counter deltas are maintained on a per-cpu basis and drained both > periodically and when the delta is above a threshold. On large CPU systems, > the difference between the estimated and real value of NR_FREE_PAGES can be > very high. If the system is under both load and low memory, it's possible > for watermarks to be breached. In extreme cases, the number of free pages > can drop to 0 leading to the possibility of system livelock. > > 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. > > Signed-off-by: Mel Gorman <mel@xxxxxxxxx> Reviewed-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx> BTW, a nitpick. > @@ -143,6 +143,9 @@ static void refresh_zone_stat_thresholds(void) > for_each_online_cpu(cpu) > per_cpu_ptr(zone->pageset, cpu)->stat_threshold > = threshold; > + > + zone->percpu_drift_mark = high_wmark_pages(zone) + > + num_online_cpus() * threshold; > } > } This function is now called only at CPU_DEAD. IOW, not called at CPU_UP_PREPARE It's done by this patch....but the reason is unclear to me. == http://git.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commitdiff;h=d1187ed21026fd512b87851d0ca26d9ae16f9059 == Christoph ? Thanks, -Kame -- 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>