Answer
The show system processes extensive command displays a RES value measured in kilobytes which represents the amount of program memory resident in the physical memory. This is also known as RSS or Resident Set Size. The RES value includes shared library pages used by the process. Any amount of memory freed by the process might still be considered part of the RES value.
Generally, the kernel delays the migrating of memory out of the Inact queue into the Cache or Free list unless there is a memory shortage. This can lead to large discrepancies between the values reported by the routing protocol process and the kernel, even after the routing protocol process has freed a large amount of memory.
For more information, see Junos OS Routing Protocols Library for Routing Devices