I know that shared memory usage in postgres was changed on 9.3 from sys v to posix so changing things like shmmax and the like aren't needed anymore (although we've trying changing those to no effect)
We've even seen out of memory errors on postgres logs a few times when the server is just using something like 8GB out of 128GB of ram
Has anyone experienced a similar issue or have seen weird memory usage patrons with CentOS 7?