On Mon, Jan 20, 2014 at 02:21:02PM -0500, r...@redhat.com wrote: > From: Rik van Riel <r...@redhat.com> > > Excessive migration of pages can hurt the performance of workloads > that span multiple NUMA nodes. However, it turns out that the > p->numa_migrate_deferred knob is a really big hammer, which does > reduce migration rates, but does not actually help performance. > > Now that the second stage of the automatic numa balancing code > has stabilized, it is time to replace the simplistic migration > deferral code with something smarter. > > Cc: Peter Zijlstra <pet...@infradead.org> > Cc: Mel Gorman <mgor...@suse.de> > Cc: Ingo Molnar <mi...@redhat.com> > Cc: Chegu Vinod <chegu_vi...@hp.com> > Signed-off-by: Rik van Riel <r...@redhat.com>
When I added a tracepoint to track deferred migration I was surprised how often it triggered for some workloads. I agree that we want to do something better because it was a crutch albeit a necessary one at the time. Note that the knob was not about performance as such, it was about avoiding worst-case behaviour. We should keep an eye out for bugs that look like excessive migration on workloads that are not converging. Reintroducing this hammer would be a last resort for working around the problem. Finally, the sysctl is documented in Documentation/sysctl/kernel.txt and this patch should also remove it. Functionally, the patch looks fine and it's time to reinvestigate if it's necessary so assuming the documentation gets removed; Acked-by: Mel Gorman <mgor...@suse.de> -- Mel Gorman SUSE Labs -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
