mm: increase RECLAIM_DISTANCE to 30
Recently, Robert Mueller reported (http://lkml.org/lkml/2010/9/12/236) that zone_reclaim_mode doesn't work 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. 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 well on it. Unfortunatelly, such models are still typical even in the 21st century. We can't ignore them. This patch raises the zone_reclaim_mode threshold to 30. 30 doesn't have any specific meaning. but 20 means that one-hop QPI/Hypertransport and such relatively cheap 2-4 socket machine are often used for traditional servers as above. The intention is that these machines don't use zone_reclaim_mode. Note: ia64 and Power have arch specific RECLAIM_DISTANCE definitions. This patch doesn't change such high-end NUMA machine behavior. Dave Hansen said: : I know specifically of pieces of x86 hardware that set the information : in the BIOS to '21' *specifically* so they'll get the zone_reclaim_mode : behavior which that implies. : : They've done performance testing and run very large and scary benchmarks : to make sure that they _want_ this turned on. What this means for them : is that they'll probably be de-optimized, at least on newer versions of : the kernel. : : If you want to do this for particular systems, maybe _that_'s what we : should do. Have a list of specific configurations that need the : defaults overridden either because they're buggy, or they have an : unusual hardware configuration not really reflected in the distance : table. And later said: : The original change in the hardware tables was for the benefit of a : benchmark. Said benchmark isn't going to get run on mainline until the : next batch of enterprise distros drops, at which point the hardware where : this was done will be irrelevant for the benchmark. I'm sure any new : hardware will just set this distance to another yet arbitrary value to : make the kernel do what it wants. :) : : Also, when the hardware got _set_ to this initially, I complained. So, I : guess I'm getting my way now, with this patch. I'm cool with it. Reported-by:Robert Mueller <robm@fastmail.fm> Signed-off-by:
KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com> Acked-by:
Christoph Lameter <cl@linux.com> Acked-by:
David Rientjes <rientjes@google.com> Reviewed-by:
KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org> Cc: "Luck, Tony" <tony.luck@intel.com> Acked-by:
Dave Hansen <dave@linux.vnet.ibm.com> Signed-off-by:
Andrew Morton <akpm@linux-foundation.org> Signed-off-by:
Linus Torvalds <torvalds@linux-foundation.org>
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