merge revision(s) r46387: [Backport #9607]
* gc.c: change full GC timing to keep lower memory usage. Extend heap only at (1) after major GC or (2) after several (two times, at current) minor GC Details in https://bugs.ruby-lang.org/issues/9607#note-9 [Bug #9607]
git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/branches/ruby_2_1@47326 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
merge revision(s) r46387: [Backport #9607]
git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/branches/ruby_2_1@47326 b2dd03c8-39d4-4d8f-98ff-823fe69b080e