On 10/14/2016 08:28 AM, Stefan Priebe - Profihost AG wrote:
Hello list,

while running the same workload on two machines (single xeon and a dual
xeon) both with 64GB RAM.

I need to run echo 3 >/proc/sys/vm/drop_caches every 15-30 minutes to
keep the speed as good as on the non numa system. I'm not sure whether
this is related to numa.

Is there any sysctl parameter to tune?

Tested with vanilla v4.8.1


why do you think this is related to btrfs?

The only known issue that has this type of workaround that I know of are transparent huge pages. This is easy to diagnose but recording some kernel stacks during the problem with perf. If there is very high system cpu usage in a spinlock called by compaction functions during page faults it is the synchronous memory defragmentation needed for thp. Should that be the case the better workaround is disabling it in /sys/kernel/mm/transparent_hugepage/defrag

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