Issue #8142 has been updated by tmm1 (Aman Gupta).


>  I'll make another feature request.
>  
>  # On a preliminary evaluation, simple (ideal) micro benchmark was
>  # 20-30% faster.

Great. I tried some GC experiments recently (additional bit per object to track longlife generation), but without write barrier it was very tricky to implement. I look forward to seeing your idea.

> However, this String object can be replaced
>  with non-VALUE memory object (not a VALUE, but a memory dump).

I am doing some experiments with this technique. For the putstring instruction, this is very simple- replace rb_str_resurrect() with rb_str_new2() using memory dumped value.

But in DSTR, putobject instruction is used instead of putstring (https://github.com/ruby/ruby/commit/49371b54). Replacing this with rb_str_new every time will increase GC pressure, so it is not ideal.

One solution is to make memory dump re-use struct RString, so it can emulate a string object (special API to allocate strings outside the ruby heap, using ALLOC(struct RString)). These objects can also contain an extra reference count field.

But if putobject instruction gives out reference to these unmanaged object, then reference count is not enough to free. An additional GC mark/sweep will be required after refcount==0, to make sure no one is still referencing the string. This is still possible (similar technique is used for unlinked method entries?). I have some patches for this approach, but I am curious what you think. Is this a bad idea?
----------------------------------------
Bug #8142: [patch] iseq: reduce array allocations for simple sequences
https://bugs.ruby-lang.org/issues/8142#change-37928

Author: tmm1 (Aman Gupta)
Status: Open
Priority: Normal
Assignee: ko1 (Koichi Sasada)
Category: 
Target version: 
ruby -v: ruby 2.1.0dev (2013-03-20 trunk 39832) [x86_64-darwin12.2.1]


Allocate iseq->mark_ary on demand, only if needed.

In my application, this reduces long lived arrays on the heap significantly.

:T_ARRAY=>88166 # before
:T_ARRAY=>62932 # after

diff --git a/compile.c b/compile.c
index 9360f5b..aafae05 100644
--- a/compile.c
+++ b/compile.c
@@ -416,7 +416,7 @@ static int
 iseq_add_mark_object(rb_iseq_t *iseq, VALUE v)
 {
     if (!SPECIAL_CONST_P(v)) {
-	rb_ary_push(iseq->mark_ary, v);
+	rb_iseq_add_mark_object(iseq, v);
     }
     return COMPILE_OK;
 }
diff --git a/insns.def b/insns.def
index 979aa1c..bb9fc3f 100644
--- a/insns.def
+++ b/insns.def
@@ -1237,7 +1237,7 @@ setinlinecache
 (VALUE val)
 {
     if (ic->ic_value.value == Qundef) {
-	rb_ary_push(GET_ISEQ()->mark_ary, val);
+	rb_iseq_add_mark_object(GET_ISEQ(), val);
     }
     ic->ic_value.value = val;
     ic->ic_vmstat = GET_VM_STATE_VERSION() - ruby_vm_const_missing_count;
diff --git a/iseq.c b/iseq.c
index 288d3bf..eab237a 100644
--- a/iseq.c
+++ b/iseq.c
@@ -237,6 +237,17 @@ set_relation(rb_iseq_t *iseq, const VALUE parent)
     }
 }
 
+void
+rb_iseq_add_mark_object(rb_iseq_t *iseq, VALUE obj)
+{
+    if (!RTEST(iseq->mark_ary)) {
+        iseq->mark_ary = rb_ary_tmp_new(3);
+        OBJ_UNTRUST(iseq->mark_ary);
+        RBASIC(iseq->mark_ary)->klass = 0;
+    }
+    rb_ary_push(iseq->mark_ary, obj);
+}
+
 static VALUE
 prepare_iseq_build(rb_iseq_t *iseq,
 		   VALUE name, VALUE path, VALUE absolute_path, VALUE first_lineno,
@@ -259,9 +270,7 @@ prepare_iseq_build(rb_iseq_t *iseq,
     }
 
     iseq->defined_method_id = 0;
-    iseq->mark_ary = rb_ary_tmp_new(3);
-    OBJ_UNTRUST(iseq->mark_ary);
-    RBASIC(iseq->mark_ary)->klass = 0;
+    iseq->mark_ary = 0;
 
 
     /*
@@ -2060,8 +2069,7 @@ rb_iseq_build_for_ruby2cext(
     iseq->location.label = rb_str_new2(name);
     iseq->location.path = rb_str_new2(path);
     iseq->location.first_lineno = first_lineno;
-    iseq->mark_ary = rb_ary_tmp_new(3);
-    OBJ_UNTRUST(iseq->mark_ary);
+    iseq->mark_ary = 0;
     iseq->self = iseqval;
 
     iseq->iseq = ALLOC_N(VALUE, iseq->iseq_size);
diff --git a/iseq.h b/iseq.h
index 0790529..4de0816 100644
--- a/iseq.h
+++ b/iseq.h
@@ -23,6 +23,7 @@ VALUE rb_iseq_build_from_ary(rb_iseq_t *iseq, VALUE locals, VALUE args,
 			     VALUE exception, VALUE body);
 
 /* iseq.c */
+void rb_iseq_add_mark_object(rb_iseq_t *iseq, VALUE obj);
 VALUE rb_iseq_load(VALUE data, VALUE parent, VALUE opt);
 VALUE rb_iseq_parameters(const rb_iseq_t *iseq, int is_proc);
 struct st_table *ruby_insn_make_insn_table(void);



-- 
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