Re: [RFC] another way to speed up fake numa node page_alloc

[David Rientjes <rientjes@cs.washington.edu>]

On Wed, 4 Oct 2006, Paul Jackson wrote:

> And as to why my position changed as to whether the zonelist scans
> were ever a performance issue on real numa, I've already answered that
> question ... a couple of times.  Let me know if you need me to repeat
> this answer a third time.
> 

No, what I need repeated a third time is why changes are being made 
without data to support it, especially to something like 
get_page_from_freelist that has never been complained about on real NUMA 
setups.  Second, what I need repeated a third time is why changes are 
being made to the real NUMA case without data to show it's a problem in 
the first place.  This is a scientific process where we can experiment and 
then collect data and analyize it to see what went right and what went 
wrong.  I'm a big supporter of making changes when you have a feeling that 
it will make a difference because often times the experiments will prove 
that it did.  But I'm not a big supporter of saying "the real NUMA case 
being slow was mentioned to me in passing once, I've never witnessed it, 
I can't describe how to test it, and I have nothing to compare it to, so 
let's add more code because it can't make it worse."

So I really don't see what the point of debating the issue is when any 
number of tests could either prove or disprove this and those tests don't 
need to be run by Rohit on a fake NUMA setup.  You have a NUMA setup with 
1024 nodes, so let's see ANY workload IN ANY CIRCUMSTANCE where the HARD 
DATA shows that it improves the case.  Theory is great for discussion, but 
real numbers actually make the case.

[ And when I return the Seattle from east LA and I try to squeeze a 64-bit
  machine out of my school, even as a lowly undergrad, I'm looking forward
  to patching your patch so that it zaps the nodemask _only_ on frees and
  showing that it works better in every scenario that I can think of. ]

		David

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