Troubleshooting sqlplus logon instance slow and Swap usage high even memory is 50% free

A few days ago, I encountered a case, a three-node Oracle RAC database on RHEL 6.6 , when trying to login to the database instance using sqlplus “/ as sysdba” on the third node, It’s very slow, and vmstat show that there is a very large swap in and out, but there is still a lot of memory free space