[Lustre-discuss] Slow read performance after ~700MB-2GB

Alexander Oltu Alexander.Oltu at uni.no
Wed Jun 9 12:41:38 PDT 2010


On Wed, 9 Jun 2010 10:29:36 -0700
Jason Rappleye wrote:

> 
> Is vm.zone_reclaim_mode set to a value other that zero?

Yes, it was 1, as soon as I set it to 0 the problem disappears. 

Thank you Jason! It was a long issue for us.

> 
> This sounds a lot like a problem we recently experienced when a BIOS  
> upgrade changed to the ACPI SLIT table, which specifies the
> distances between NUMA nodes in a system. It put the remote node
> distance over the threshold the kernel uses to decide whether or not
> to enable the inline zone reclaim path. At least on SLES, Lustre
> doesn't seem to be able to free up pages in the page cache in this
> path, and performance dropped to 2-4MB/s. In my test case I was
> issuing 2MB I/Os and the kernel only let 1-2 I/Os trickle out per
> second, so that matches up with what you're seeing.
> 
> j
> 
> 



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