out-of-memory-warning-percentage

out-of-memory-warning-percentage is a variable defined in `files.el'.
Its value is

nil

Documentation:
Warn if file size exceeds this percentage of available free memory.
When nil, never issue warning. Beware: This probably doesn't do what you
think it does, because "free" is pretty hard to define in practice.

You can customize this variable.

This variable was introduced, or its default value was changed, in version 25.1 of Emacs.