@dsecareanu are you able to correlate the memory usage with sites that receive a lot of image uploads?
We’re aware that in certain situations the default memory allocator in Ubuntu can have issues where memory used by the image processor is not freed back to the OS. This can be resolved by using jemalloc as the memory allocator.
For reference we see typical memory usage for reasonably sized sites sitting at ~180-200MB. For very large sites (10s-100s of thousands of posts/tags) this can obviously be higher.