Messages in this thread | | | From | KOSAKI Motohiro <> | Subject | Re: [PATCH 4/4] zone_reclaim_mode is always 0 by default | Date | Tue, 19 May 2009 11:53:44 +0900 (JST) |
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Hi
> > Current linux policy is, zone_reclaim_mode is enabled by default if the machine > > has large remote node distance. it's because we could assume that large distance > > mean large server until recently. > > > > Unfortunately, recent modern x86 CPU (e.g. Core i7, Opeteron) have P2P transport > > memory controller. IOW it's seen as NUMA from software view. > > > > Some Core i7 machine has large remote node distance, but zone_reclaim don't > > fit desktop and small file server. it cause performance degression. > > > > Thus, zone_reclaim == 0 is better by default if the machine is small. > > What if I had a node 0 with 32GB or 128GB of memory. In that case, > we would have 3GB for DMA32, 125GB for Normal and then a node 1 with > 128GB. I would suggest that zone reclaim would perform normally and > be beneficial. > > You are unfairly classifying this as a size of machine problem when it is > really a problem with the underlying zone reclaim code being triggered > due to imbalanced node/zones, part of which is due to a single node > having multiple zones and those multiple zones setting up the conditions > for extremely agressive reclaim. In other words, you are putting a > bandage in place to hide a problem on your particular hardware. > > Can RECLAIM_DISTANCE be adjusted so your Ci7 boxes are no longer caught? > Aren't 4 node Ci7 boxes soon to be readily available? How are your apps > different from my apps in that you are not impacted by node locality? > Are you being too insensitive to node locality? Conversely am I being > too sensitive? > > All that said, I would not stop this from going in. I just think the > selection criteria is rather random. I think we know the condition we > are trying to avoid which is a small Normal zone on one node and a larger > Normal zone on another causing zone reclaim to be overly agressive. > I don't know how to quantify "small" versus "large". I would suggest > that a node 0 with 16 or more GB should have zone reclaim on by default > as well. Can that be expressed in the selection criteria.
I post my opinion as another mail. please see it.
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