On Mon, Jan 27, 2014 at 05:03:45PM -0500, riel@xxxxxxxxxx wrote: > From: Rik van Riel <riel@xxxxxxxxxx> > > Tracing the code that decides the active nodes has made it abundantly clear > that the naive implementation of the faults_from code has issues. > > Specifically, the garbage collector in some workloads will access orders > of magnitudes more memory than the threads that do all the active work. > This resulted in the node with the garbage collector being marked the only > active node in the group. > > This issue is avoided if we weigh the statistics by CPU use of each task in > the numa group, instead of by how many faults each thread has occurred. > > To achieve this, we normalize the number of faults to the fraction of faults > that occurred on each node, and then multiply that fraction by the fraction > of CPU time the task has used since the last time task_numa_placement was > invoked. > > This way the nodes in the active node mask will be the ones where the tasks > from the numa group are most actively running, and the influence of eg. the > garbage collector and other do-little threads is properly minimized. > > On a 4 node system, using CPU use statistics calculated over a longer interval > results in about 1% fewer page migrations with two 32-warehouse specjbb runs > on a 4 node system, and about 5% fewer page migrations, as well as 1% better > throughput, with two 8-warehouse specjbb runs, as compared with the shorter > term statistics kept by the scheduler. > > Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx> > Cc: Mel Gorman <mgorman@xxxxxxx> > Cc: Ingo Molnar <mingo@xxxxxxxxxx> > Cc: Chegu Vinod <chegu_vinod@xxxxxx> > Signed-off-by: Rik van Riel <riel@xxxxxxxxxx> Major changes are related to the weight calculations to avoid overflow and the avg runtime is calculated based on a longer runtime than the v4 version. Both seem sane so Acked-by: Mel Gorman <mgorman@suse> -- Mel Gorman SUSE Labs -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>