it's an old issue basically the extension doesn't know which file is the root/main of your project, so it has to open a nimsuggest file for each .nim file you open/edit. Question is why those processes not always die automatically when files are closed.
You can do 2 thigs: * proper one: as already suggested, specify a project file via the "nim.project" setting or settings.json file inside .vscode in your project * help the world: dig into the problem and find out why nimsuggest processes are not killed and slowly eats all system memory there are existing issues opened on this on github
