The default value is either one or zero depending on the distance between nodes as reported by the numactl utility. If the distance is over 20 zone_reclaim_mode will default to one. The Nehalem nodes report a distance of 21, SandyBridge and IvyBridge are lower.
-- ddj Dave Johnson > On Sep 19, 2014, at 1:42 PM, Christopher Samuel <[email protected]> wrote: > >> On 20/09/14 03:27, Christopher Samuel wrote: >> >> To be honest I'm suspicious of kernel autotuning here.. > > OK, did a quick bit of poking around. > > On our M4 iDataplex I see 0 everywhere. > > *but* on our M2 cluster I see: > > [root@merri-m ~]# xdsh all -v cat /proc/sys/vm/zone_reclaim_mode | xcoll > ==================================== > idataplex,login,terri > ==================================== > 1 > > ==================================== > merri081,merri083,turpin,merri082 > ==================================== > 0 > > So all the M2's have 1, along with an (old, 2011, Westmere) SGI UV10. > > The nodes that are all 0 are x3690 X5 (Westmere with Maxx5's). > > Now they're all booting the same statelite image and so I know it's > not something we've configured: > > provmethod=rhel64_gpfs35016_updates > > So I'd say that's highly likely to be kernel autotuning. > > > Aha - there was a patch merged for 3.16 to disable it by default! > > commit 4f9b16a64753d0bb607454347036dc997fd03b82 > Author: Mel Gorman <[email protected]> > Date: Wed Jun 4 16:07:14 2014 -0700 > > mm: disable zone_reclaim_mode by default > > When it was introduced, zone_reclaim_mode made sense as NUMA distances > punished and workloads were generally partitioned to fit into a NUMA > node. NUMA machines are now common but few of the workloads are > NUMA-aware and it's routine to see major performance degradation due to > zone_reclaim_mode being enabled but relatively few can identify the > problem. > > Those that require zone_reclaim_mode are likely to be able to detect > when it needs to be enabled and tune appropriately so lets have a > sensible default for the bulk of users. > > > That modified the text describing the sysctl in vm.txt, and that > old text confirms that the kernel does autotune this.. > > zone_reclaim_mode is set during bootup to 1 if it is determined that pages > from remote zones will cause a measurable performance reduction. The > page allocator will then reclaim easily reusable pages (those page > cache pages that are currently not used) before allocating off node pages. > > So there you go! > > Best of luck, > Chris (off to catch a plane) > -- > Christopher Samuel Senior Systems Administrator > VLSCI - Victorian Life Sciences Computation Initiative > Email: [email protected] Phone: +61 (0)3 903 55545 > http://www.vlsci.org.au/ http://twitter.com/vlsci > > > ------------------------------------------------------------------------------ > Slashdot TV. Video for Nerds. Stuff that Matters. > http://pubads.g.doubleclick.net/gampad/clk?id=160591471&iu=/4140/ostg.clktrk > _______________________________________________ > xCAT-user mailing list > [email protected] > https://lists.sourceforge.net/lists/listinfo/xcat-user ------------------------------------------------------------------------------ Slashdot TV. Video for Nerds. Stuff that Matters. http://pubads.g.doubleclick.net/gampad/clk?id=160591471&iu=/4140/ostg.clktrk _______________________________________________ xCAT-user mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/xcat-user
