PostgreSQL 9.3 abd CentOS 7 memory usage

Hello all,

I have a question regarding the memory usage I'm seeing in one of my
servers. This servers was recently installed using CentOS 7 and PostgreSQL
9.3

The server has 128GB of ram and we've configured postgresql.conf to use as
much memory as it can (it's a dedicate postgres server after all)

What we're seeing is that even at high peaks of load the server doesn't
consume more than 14GB, increasing the load doesn't increase ram usage
equally. We find this odd since we've other servers that are CentOS 6.5 and
postgres 9.3 and postgres 8.4, and all use all the ram available.

This particular server was a CentOS 6.5 and postgres 9.1 before and was
able to use all 128GB of ram, now it doesn't for some reason.

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?