Variable: set-mark-command-repeat-pop

Non-nil means repeating C-SPC after popping mark pops it again.
That means that C-u C-SPC C-SPC
will pop the mark twice, and
C-u C-SPC C-SPC C-SPC
will pop the mark three times.

A value of nil means C-SPC's behavior does not change after C-u C-SPC.