[Open] Make a cap for malloc_limit adjustment

Issue #9687 has been reported by Koichi Sasada.


Bug #9687: Make a cap for malloc_limit adjustment
https://bugs.ruby-lang.org/issues/9687

  • Author: Koichi Sasada
  • Status: Open
  • Priority: Normal
  • Assignee: Koichi Sasada
  • Category: core
  • Target version: current: 2.2.0
  • ruby -v: 2.2
  • Backport: 2.0.0: UNKNOWN, 2.1: UNKNOWN

The blog post [Ruby Garbage Collection: Still Not Ready for Production]
(http://www.omniref.com/blog/blog/2014/03/27/ruby-garbage-collection-still-not-ready-for-production/)
pointed out that the following code consumes all of memory:

while true
  "a" * (1024 ** 2)
end

This is because `malloc_limit’ grows and grows infinitely.

The following patch will solve this issue.

Index: gc.c
===================================================================
--- gc.c  (revision 45433)
+++ gc.c  (working copy)
@@ -2890,7 +2890,7 @@ gc_before_sweep(rb_objspace_t *objspace)
       malloc_limit = (size_t)(inc * 
gc_params.malloc_limit_growth_factor);
       if (gc_params.malloc_limit_max > 0 && /* ignore max-check if 0 */
     malloc_limit > gc_params.malloc_limit_max) {
-    malloc_limit = inc;
+    malloc_limit = gc_params.malloc_limit_max;
       }
   }
   else {

Maybe this patch should be applied for 2.1.x series.

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