global-undo-tree-mode Dramatic freezes on routine “undo” I was experiencing freezes of sometimes up to 30 seconds about 3/4 of the the time when I used my muscle memory to hit undo (C-/), which I do as part of my regular “kill-line undo” combo (C-k C-/). Something must have changed recently because I started to have show-stopping freezes of my emacs thread when I tried a routine “undo.” I finally managed to squeeze a toggle-debug-on-quit and, with a bit of patience, got a C-g in during the freeze.