Ram overusage

When launching Minecraft from the launcher Minecraft assigns 1GB when out_of_game.
When I load a world the assigned ram goes up to 2GB and after playing a while up to 3GB. When this happens the Ram is completely full and freeze the OS.
Even though ingame debug overlay only shows only up to 40% usage of assigned Ram.

I have attached a diagram of Ram usage while playing. Notice how the Ram usage increases even after world has loaded. This goes on until Ram is full. (The image depicts about 30 seconds)

Sincerely, Pixdigit.