On Mon, 11 Apr 2011 17:19:31 +0900 (JST) KOSAKI Motohiro <kosaki.motohiro@xxxxxxxxxxxxxx> wrote: > Recently, Robert Mueller reported zone_reclaim_mode doesn't work It's time for some nagging. I'm trying to work out what the user-visible effect of this problem was, but it isn't described in the changelog and there is no link to any report and not even a Reported-by: or a Cc: and a search for Robert in linux-mm and linux-kernel turned up blank. > properly on his new NUMA server (Dual Xeon E5520 + Intel S5520UR MB). > He is using Cyrus IMAPd and it's built on a very traditional > single-process model. > > * a master process which reads config files and manages the other > process > * multiple imapd processes, one per connection > * multiple pop3d processes, one per connection > * multiple lmtpd processes, one per connection > * periodical "cleanup" processes. > > Then, there are thousands of independent processes. The problem is, > recent Intel motherboard turn on zone_reclaim_mode by default and > traditional prefork model software don't work fine on it. > Unfortunatelly, Such model is still typical one even though 21th > century. We can't ignore them. > > This patch raise zone_reclaim_mode threshold to 30. 30 don't have > specific meaning. but 20 mean one-hop QPI/Hypertransport and such > relatively cheap 2-4 socket machine are often used for tradiotional > server as above. The intention is, their machine don't use > zone_reclaim_mode. > > Note: ia64 and Power have arch specific RECLAIM_DISTANCE definition. > then this patch doesn't change such high-end NUMA machine behavior. > > Signed-off-by: KOSAKI Motohiro <kosaki.motohiro@xxxxxxxxxxxxxx> > Acked-by: Christoph Lameter <cl@xxxxxxxxx> > Acked-by: David Rientjes <rientjes@xxxxxxxxxx> > Reviewed-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx> > --- > include/linux/topology.h | 2 +- > 1 files changed, 1 insertions(+), 1 deletions(-) > > diff --git a/include/linux/topology.h b/include/linux/topology.h > index b91a40e..fc839bf 100644 > --- a/include/linux/topology.h > +++ b/include/linux/topology.h > @@ -60,7 +60,7 @@ int arch_update_cpu_topology(void); > * (in whatever arch specific measurement units returned by node_distance()) > * then switch on zone reclaim on boot. > */ > -#define RECLAIM_DISTANCE 20 > +#define RECLAIM_DISTANCE 30 Any time we tweak a magic number to improve one platform, we risk causing deterioration on another. Do we know that this risk is low with this patch? Also, what are we doing setting zone_relaim_mode = 1; when we have nice enumerated constants for this? It should be zone_relaim_mode = RECLAIM_ZONE; or, pedantically but clearer: zone_relaim_mode = RECLAIM_ZONE & !RECLAIM_WRITE & !RECLAIM_SWAP; Finally, we shouldn't be playing these guessing games in the kernel at all - we'll always get it wrong for some platforms and for some workloads. zone_reclaim_mdoe is tunable at runtime and we should be encouraging administrators, integrators and distros to *use* this ability. That might mean having to write some tools to empirically determine the optimum setting for a particular machine. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxxx For more info on Linux MM, see: http://www.linux-mm.org/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>