Re: btrfs and numa - needing drop_caches to keep speed up

[Stefan Priebe - Profihost AG <s.priebe@profihost.ag>]

Dear julian,

Am 14.10.2016 um 14:26 schrieb Julian Taylor:
> 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
>>
>> Greets,
>> Stefan
> 
> hi,
> why do you think this is related to btrfs?

was just an idea as i couldn't find any other difference between those
systems.

> This is easy to diagnose but recording some kernel stacks during the >
problem with perf.

you just mean perf top? Does it also show locking problems? As i see not
much CPU usage in that case.

> The only known issue that has this type of workaround that I know of are
> transparent huge pages.

I already disabled thp by:
echo never > /sys/kernel/mm/transparent_hugepage/enabled

cat /proc/meminfo says:
HugePages_Total:       0
HugePages_Free:        0
HugePages_Rsvd:        0
HugePages_Surp:        0



Greets,
Stefan

> 
> cheers,
> Julian