On Mon, 28 Jan 2013, Andrew Morton wrote: > On Fri, 25 Jan 2013 17:54:53 -0800 (PST) > Hugh Dickins <hu...@google.com> wrote: > > > --- mmotm.orig/Documentation/vm/ksm.txt 2013-01-25 14:36:31.724205455 > > -0800 > > +++ mmotm/Documentation/vm/ksm.txt 2013-01-25 14:36:38.608205618 -0800 > > @@ -58,6 +58,13 @@ sleep_millisecs - how many milliseconds > > e.g. "echo 20 > /sys/kernel/mm/ksm/sleep_millisecs" > > Default: 20 (chosen for demonstration purposes) > > > > +merge_across_nodes - specifies if pages from different numa nodes can be > > merged. > > + When set to 0, ksm merges only pages which physically > > + reside in the memory area of same NUMA node. It brings > > + lower latency to access to shared page. Value can be > > + changed only when there is no ksm shared pages in > > system. > > + Default: 1 > > + > > The explanation doesn't really tell the operator whether or not to set > merge_across_nodes for a particular machine/workload. > > I guess most people will just shrug, turn the thing on and see if it > improved things, but that's rather random.
Right. I don't think we can tell them which is going to be better, but surely we could do a better job of hinting at the tradeoffs. I think we expect large NUMA machines with lots of memory to want the better NUMA behavior of !merge_across_nodes, but machines with more limited memory across short-distance NUMA nodes, to prefer the greater deduplication of merge_across nodes. Petr, do you have a more informative text for this? Hugh -- 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/
