does need to disable 'rpc_keepalive' if 'rpc_max_threads' is get larger?

[pprun]

rpc_max_threads is set to 2048 and the 'rpc_server_type' is 'hsha', 
after 2 days running, observed that there's a high I/O activity and the 
number of 'RCP thread' grow to '2048' and VisualVm shows most of them is 
'waiting'/'sleeping' (color: yellow).

I want to know if I set rpc_keepalive to false, disable it, this will 
help to shrink the idle rpc threads?

I remembered java 8 comes with newWorkStealingPool: number of threads 
may grow and shrink dynamically.