Merge remote-tracking branch 'detsys/parallel-mark' into multithreaded-eval-v2

Author: edolstra

packaging/dependencies.nix

@@ -55,7 +55,13 @@ scope: {
       enableLargeConfig = true;
     }).overrideAttrs
       (attrs: {
-        patches = attrs.patches or [ ] ++ [ ./patches/bdwgc-bigger-mark-stack.patch ];
+        # Increase the initial mark stack size to avoid stack
+        # overflows, since these inhibit parallel marking (see
+        # GC_mark_some()). To check whether the mark stack is too
+        # small, run Nix with GC_PRINT_STATS=1 and look for messages
+        # such as `Mark stack overflow`, `No room to copy back mark
+        # stack`, and `Grew mark stack to ... frames`.
+        NIX_CFLAGS_COMPILE = "-DINITIAL_MARK_STACK_SIZE=1048576";
       });
 
   # TODO Hack until https://github.com/NixOS/nixpkgs/issues/45462 is fixed.