From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx113.postini.com [74.125.245.113]) by kanga.kvack.org (Postfix) with SMTP id B8AF46B0007 for ; Mon, 28 Jan 2013 20:17:21 -0500 (EST) Received: by mail-pb0-f42.google.com with SMTP id wz17so577460pbc.29 for ; Mon, 28 Jan 2013 17:17:21 -0800 (PST) Date: Mon, 28 Jan 2013 17:17:24 -0800 (PST) From: Hugh Dickins Subject: Re: [PATCH 1/11] ksm: allow trees per NUMA node In-Reply-To: <20130128150304.2e7a2fb4.akpm@linux-foundation.org> Message-ID: References: <20130128150304.2e7a2fb4.akpm@linux-foundation.org> MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: owner-linux-mm@kvack.org List-ID: To: Andrew Morton Cc: Petr Holasek , Andrea Arcangeli , Izik Eidus , Rik van Riel , David Rientjes , Anton Arapov , linux-kernel@vger.kernel.org, linux-mm@kvack.org On Mon, 28 Jan 2013, Andrew Morton wrote: > On Fri, 25 Jan 2013 17:54:53 -0800 (PST) > Hugh Dickins 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, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org