[Gllug] HugePages

[Kostas Georgiou]

On Thu, Oct 28, 2010 at 06:02:53PM +0100, Steve Parker wrote:

> The reason I ask, is that we have a 72Gb server running JRockit with 
> 48Gb+ JVMs in a 60Gb block of hugepages; with no swapping, and 3Gb free 
> of the 12Gb "normal" memory that is left, performance is dismal - "ls" 
> in an empty directory can take many seconds. If we bring down the 
> hugepages, things seem much better. But the apps guys say that their JVM 
> has to be all in hugepages, so if there's only 20Gb hugepages, then 
> their JVM can't store more than 20Gb data in RAM (which is the design 
> that we have been told we must work with).
> 
> Does anybody have much experience with hugepages? This is RHEL5.3, on 2 
> x quad-core hyperthreaded Intel Xeon 5570s

Remember that you are in a NUMA machine, you have 12Gb/3Gb available/free
memory after your hugepages but it doesn't mean that all nodes have
memory left. Your ls could be running in a memory starved node and you
can guess the rest. I'll be interested to see what numactl --hardware
gives after boot and later on.

Here is an interesting article for the effects of NUMA in mysql
http://jcole.us/blog/archives/2010/09/28/mysql-swap-insanity-and-the-numa-architecture/

Kostas
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