On Sat, 2010-10-30 at 03:40 +0800, Andrew Morton wrote: > On Fri, 29 Oct 2010 11:12:11 +0100 > Mel Gorman <mel@xxxxxxxxx> wrote: > > > On Thu, Oct 28, 2010 at 03:04:33PM -0700, Andrew Morton wrote: > > > On Thu, 28 Oct 2010 16:13:35 +0100 > > > > > > > > I have a feeling this problem will bite us again perhaps due to those > > > other callsites, but we haven't found the workload yet. > > > > > > I don't undestand why restore/reduce_pgdat_percpu_threshold() were > > > called around that particular sleep in kswapd and nowhere else. > > > > > > > vanilla 11.6615% > > > > disable-threshold 0.2584% > > > > > > Wow. That's 12% of all CPUs? How many CPUs and what workload? > > > > > > > 112 threads CPUs 14 sockets. Workload initialisation creates NR_CPU sparse > > files that are 10*TOTAL_MEMORY/NR_CPU in size. Workload itself is NR_CPU > > processes just reading their own file. > > > > The critical thing is the number of sockets. For single-socket-8-thread > > for example, vanilla was just 0.66% of time (although the patches did > > bring it down to 0.11%). > > I'm surprised. I thought the inefficiency here was caused by CPUs > tromping through percpu data, adding things up. But the above info > would indicate that the problem was caused by lots of cross-socket > traffic? If so, where did that come from? >From my understanding, the problem is zone_nr_free_pages() will try to read each cpu's ->vm_stat_diff, while other CPUs are changing their vm_stat_diff. This will cause a lot of cache bounce. -- 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/ . Fight unfair telecom policy in Canada: sign http://dissolvethecrtc.ca/ Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>