* Set libgc's initial heap size to 384 MiB to prevent garbage

  collection in most cases (and therefore its performance overhead).

1 files changed, 12 insertions, 0 deletions

diff --git a/src/libmain/shared.cc b/src/libmain/shared.cc
index 440949bd2a..82309544a6 100644
--- a/src/libmain/shared.cc
+++ b/src/libmain/shared.cc
@@ -353,6 +353,18 @@ int main(int argc, char * * argv)
     GC_INIT();
 
     GC_oom_fn = oomHandler;
+
+    /* Set the initial heap size to something fairly big (384 MiB) so
+       that in most cases we don't need to garbage collect at all.
+       (Collection has a fairly significant overhead, some.)  The heap
+       size can be overriden through libgc's GC_INITIAL_HEAP_SIZE
+       environment variable.  We should probably also provide a
+       nix.conf setting for this.  Note that GC_expand_hp() causes a
+       lot of virtual, but not physical (resident) memory to be
+       allocated.  This might be a problem on systems that don't
+       overcommit. */
+    if (!getenv("GC_INITIAL_HEAP_SIZE"))
+        GC_expand_hp(384000000);
 #endif
 
     try {