Description of problem:

I have created 111 VMS on 1 host and turned them on.
After the VMS where up, the VDSM process took 300 MB of RAM.
Now, 6 day's later, with the system idle - no actions are done on the engine or the VMS, the VDSM takes ~630 GB of RAM as seen below :

PID USER      PR  NI    VIRT    RES    SHR S  %CPU %MEM     TIME+ COMMAND                                                                                                                                          
18100 vdsm    0   -20  9980.2m 634340  11260 S  14.1  1.0 379:42.58 vdsm 


Version-Release number of selected component (if applicable):

VDSM = 4.18.11

How reproducible:
100%

Steps to Reproduce:
1.create 111 VDSM
2.measure the VDSM memory after 6 day's

Actual results:
VDSM memory doubled it's size in 6 days time.

Expected results:
after VMS are up, VDSM memory should stay the same.

Additional info:
No errors are seen at the VDSM logs.