User-Agent:       Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101
Firefox/52.0
Build Identifier: 

Up to 50% CPU load when copy files from NAS (NFS share) to local HDD disk. 

Reproducible: Always

Steps to Reproduce:
1. Mount //nas_server/media to /home/user/NAS
2. copy bunch of 2-20MB files from /home/user/NAS to /home/user/photos
3. open system monitor 

My hardware: Intel i7-4771; 24GB RAM; PCI Intel PRO/1000PT Dual port Server
adapter. 
NFS share mounted /home/users/NAS; copying files to sdc1 /home/user/photos; No
volume encryption on local host.
Local network: GBit LAN; NAS GBit; NFS share; 
Actual Results:  
Up to 50% CPU load when copy files from NAS with NFS share with 1GBit LAN
interfaces to local host disc. System monitor showing on all 8 CPU cores 30-70%
load, in total average 46-58% when  Network receiving 28MiB/s, sending
0.3MiB/s. 
System lags during copy. 

System activity: CPU% - Memory - Shared Memory 
+systemd 34% - 2,024K - 3,964K
+kdeinit5: 25% - 3,160K - 18,164K
-+ksmserver 21% - 5,6,44K - 35,780K
--+pasmashell 21%321,960K - 110,832 K
-+firefox 1% - 2,416,999K - 142,856K
+sddm 8% - 1,208K - 11,752K
-+X 8% - 84,280K - 106,728K


Expected Results:  
Expected up to 10% CPU load. 

No partition or volume encryption.
At least I never have issues when on Windows OS with same setup.
Very often working with lots of media files from NAS. 
KDE plasma: 5.8.7
KDE Frame: 5.32.0
Qt: 5.6.2
Kernel: 4.4.79-19
64Bit