lkml.org 
[lkml]   [2013]   [Jan]   [28]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH 1/11] ksm: allow trees per NUMA node
On Mon, 28 Jan 2013, Andrew Morton wrote:
> On Fri, 25 Jan 2013 17:54:53 -0800 (PST)
> Hugh Dickins <hughd@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


\
 
 \ /
  Last update: 2013-01-29 03:21    [W:0.125 / U:3.412 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site