RAM doesn’t go down because that’s how Linux and memory management work. It will shift from being used one way to another.
PMS itself allocates memory on demand. Once allocated, it remains allocated. This is done to prevent memory fragmentation and degrade system performance.
Points of info:
Please always state specific PMS version as there are almost always two versions ‘current’
Please also state which Linux distro and version as there are multiple versions supported for each distro.