diff --git a/src/nasal_dbg.cpp b/src/nasal_dbg.cpp
index 35a85a4..94cbfd8 100644
--- a/src/nasal_dbg.cpp
+++ b/src/nasal_dbg.cpp
@@ -290,7 +290,7 @@ void dbg::run(const codegen& gen,
             counter.dump_all_code_line_counter(std::clog):
             counter.dump_this_file_line_counter(std::clog);
     }
-    ngc.info();
+    ngc.status.dump_info();
     ngc.clear();
     imm.clear();
     return;
diff --git a/src/nasal_gc.cpp b/src/nasal_gc.cpp
index fab1854..ba56bc4 100644
--- a/src/nasal_gc.cpp
+++ b/src/nasal_gc.cpp
@@ -1,5 +1,4 @@
 #include "nasal_gc.h"
-#include "util/util.h"
 
 namespace nasal {
 
@@ -31,10 +30,9 @@ void gc::mark() {
     std::vector<var> bfs;
     mark_context_root(bfs);
 
-    // concurrent mark, experimental
-    if (memory.size() > gc::concurrent_threshold() && bfs.size() > 16) {
-        status.flag_concurrent_mark_triggered = true;
-        usize size = bfs.size();
+    // concurrent mark
+    if (memory.size() > UINT16_MAX * 16 && bfs.size() > 16) {
+        auto size = bfs.size();
         std::thread t0(&gc::concurrent_mark, this, std::ref(bfs), 0, size/4);
         std::thread t1(&gc::concurrent_mark, this, std::ref(bfs), size/4, size/2);
         std::thread t2(&gc::concurrent_mark, this, std::ref(bfs), size/2, size/4*3);
@@ -297,147 +295,6 @@ void gc::clear() {
     env_argv.clear();
 }
 
-void gc::info() const {
-    util::windows_code_page_manager wm;
-    wm.set_utf8_output();
-
-    using std::left;
-    using std::setw;
-    using std::setfill;
-    using std::setprecision;
-
-    const char* used_table_name[] = {
-        "object type",
-        "gc cycle",
-        "alloc count",
-        "object count",
-        "detail",
-        "time spend",
-        "gc time",
-        "avg time",
-        "max gc",
-        "max mark",
-        "max sweep",
-        nullptr
-    };
-    const char* name[] = {
-        "string",
-        "vector",
-        "hashmap",
-        "function",
-        "upvalue",
-        "ghost",
-        "coroutine",
-        "namespace",
-        nullptr
-    };
-
-    usize indent = 0, len = 0;
-    for(usize i = 0; used_table_name[i]; ++i) {
-        len = std::string(used_table_name[i]).length();
-        indent = indent<len? len:indent;
-    }
-    for(usize i = 0; name[i]; ++i) {
-        len = std::string(name[i]).length();
-        indent = indent<len? len:indent;
-    }
-    for(u32 i = 0; i<GC_TYPE_SIZE; ++i) {
-        len = std::to_string(status.gc_cycle_trigger_count[i]).length();
-        indent = indent<len? len:indent;
-        len = std::to_string(status.alloc_count[i]).length();
-        indent = indent<len? len:indent;
-        len = std::to_string(status.object_size[i]).length();
-        indent = indent<len? len:indent;
-    }
-    auto indent_string = std::string("──");
-    for(usize i = 0; i<indent; ++i) {
-        indent_string += "─";
-    }
-    const auto first_line = "╭" + indent_string + "┬" +
-                            indent_string + "┬" +
-                            indent_string + "┬" +
-                            indent_string + "╮";
-    const auto second_line = "├" + indent_string + "┼" +
-                             indent_string + "┼" +
-                             indent_string + "┼" +
-                             indent_string + "┤";
-    const auto mid_line = "├" + indent_string + "┼" +
-                          indent_string + "┴" +
-                          indent_string + "┴" +
-                          indent_string + "┤";
-    const auto another_mid_line = "├" + indent_string + "┼" +
-                                  indent_string + "─" +
-                                  indent_string + "─" +
-                                  indent_string + "┤";
-    const auto last_line = "╰" + indent_string + "┴" +
-                           indent_string + "─" +
-                           indent_string + "─" +
-                           indent_string + "╯";
-
-    std::clog << "\n" << first_line << "\n";
-    std::clog << "│ " << left << setw(indent) << setfill(' ') << "object type";
-    std::clog << " │ " << left << setw(indent) << setfill(' ') << "gc cycle";
-    std::clog << " │ " << left << setw(indent) << setfill(' ') << "alloc count";
-    std::clog << " │ " << left << setw(indent) << setfill(' ') << "object count";
-    std::clog << " │\n" << second_line << "\n" << std::internal;
-
-    double total = 0;
-    for(u8 i = 0; i<GC_TYPE_SIZE; ++i) {
-        if (!status.gc_cycle_trigger_count[i] &&
-            !status.alloc_count[i] &&
-            !status.object_size[i]) {
-            continue;
-        }
-        total += static_cast<f64>(status.gc_cycle_trigger_count[i]);
-        std::clog << "│ " << left << setw(indent) << setfill(' ') << name[i];
-        std::clog << " │ " << left << setw(indent) << setfill(' ') << status.gc_cycle_trigger_count[i];
-        std::clog << " │ " << left << setw(indent) << setfill(' ') << status.alloc_count[i];
-        std::clog << " │ " << left << setw(indent) << setfill(' ') << status.object_size[i];
-        std::clog << " │\n" << std::internal;
-    }
-    std::clog << mid_line << "\n";
-
-    const auto den = std::chrono::high_resolution_clock::duration::period::den;
-    std::clog << "│ " << left << setw(indent) << setfill(' ') << "detail";
-    std::clog << " │ " << left << setw(indent) << setfill(' ') << "time spend";
-    std::clog << "   " << left << setw(indent) << setfill(' ') << " ";
-    std::clog << "   " << left << setw(indent) << setfill(' ') << " ";
-    std::clog << " │\n" << another_mid_line << "\n";
-
-    std::clog << "│ " << left << setw(indent) << setfill(' ') << "gc time";
-    std::clog << " │ " << setw(indent-3) << setprecision(4) << status.gc_time_ms() << " ms";
-    std::clog << setw(indent*2+7) << " " << "│\n";
-
-    std::clog << "│ " << left << setw(indent) << setfill(' ') << "avg time";
-    std::clog << " │ " << setw(indent-3) << setprecision(4) << status.avg_time_ms() << " ms";
-    std::clog << setw(indent*2+7) << " " << "│\n";
-
-    std::clog << "│ " << left << setw(indent) << setfill(' ') << "avg mark";
-    std::clog << " │ " << setw(indent-3) << setprecision(4) << status.avg_mark_time_ms() << " ms";
-    std::clog << setw(indent*2+7) << " " << "│\n";
-
-    std::clog << "│ " << left << setw(indent) << setfill(' ') << "avg sweep";
-    std::clog << " │ " << setw(indent-3) << setprecision(4) << status.avg_sweep_time_ms() << " ms";
-    std::clog << setw(indent*2+7) << " " << "│\n";
-
-    std::clog << "│ " << left << setw(indent) << setfill(' ') << "max mark";
-    std::clog << " │ " << setw(indent-3) << setprecision(4) << status.max_mark_time_ms() << " ms";
-    std::clog << setw(indent*2+7) << " " << "│\n";
-
-    std::clog << "│ " << left << setw(indent) << setfill(' ') << "max sweep";
-    std::clog << " │ " << setw(indent-3) << setprecision(4) << status.max_sweep_time_ms() << " ms";
-    std::clog << setw(indent*2+7) << " " << "│\n";
-
-    std::clog << "│ " << left << setw(indent) << setfill(' ') << "concurrent";
-    std::clog << " │ " << setw(indent)
-              << (status.flag_concurrent_mark_triggered? "true":"false");
-    std::clog << setw(indent*2+7) << " " << "│\n";
-
-    std::clog << last_line << "\n" << std::internal;
-
-    wm.restore_code_page();
-}
-
 var gc::alloc(const vm_type type) {
     const u32 index = static_cast<u32>(type)-static_cast<u32>(vm_type::vm_str);
     ++status.alloc_count[index];
diff --git a/src/nasal_gc.h b/src/nasal_gc.h
index 18c384f..c44e137 100644
--- a/src/nasal_gc.h
+++ b/src/nasal_gc.h
@@ -95,15 +95,10 @@ private:
     void mark_map(std::vector<var>&, nas_map&);
     void sweep();
 
-    static const auto concurrent_threshold() {
-        return UINT16_MAX * 16;
-    }
-
 public:
     void extend(const vm_type);
     void init(const std::vector<std::string>&, const std::vector<std::string>&);
     void clear();
-    void info() const;
     var alloc(const vm_type);
     void context_change(nas_co*);
     void context_reserve();
diff --git a/src/nasal_opcode.h b/src/nasal_opcode.h
index 0b9fa1a..9201ff8 100644
--- a/src/nasal_opcode.h
+++ b/src/nasal_opcode.h
@@ -215,8 +215,7 @@ public:
                     const nasal_builtin_table*,
                     const std::string* file_list = nullptr);
     void dump(std::ostream&) const;
+    friend std::ostream& operator<<(std::ostream&, const codestream&);
 };
 
-std::ostream& operator<<(std::ostream&, const codestream&);
-
 }
\ No newline at end of file
diff --git a/src/nasal_vm.cpp b/src/nasal_vm.cpp
index 0dcfaaa..96b9388 100644
--- a/src/nasal_vm.cpp
+++ b/src/nasal_vm.cpp
@@ -717,7 +717,7 @@ void vm::run(const codegen& gen,
 // all nasal programs should end here
 vmexit:
     if (verbose) {
-        ngc.info();
+        ngc.status.dump_info();
     }
     imm.clear();
     if (!is_repl_mode) {
diff --git a/src/util/gc_stat.cpp b/src/util/gc_stat.cpp
index 5bac2f6..d6631e5 100644
--- a/src/util/gc_stat.cpp
+++ b/src/util/gc_stat.cpp
@@ -1,6 +1,8 @@
+#include "util/util.h"
 #include "util/gc_stat.h"
 
 #include <chrono>
+#include <iomanip>
 
 namespace nasal {
 
@@ -19,8 +21,6 @@ void gc_stat::init() {
 
     max_mark_time = 0;
     max_sweep_time = 0;
-
-    flag_concurrent_mark_triggered = false;
 }
 
 f64 gc_stat::gc_time_ms() const {
@@ -56,4 +56,138 @@ f64 gc_stat::max_sweep_time_ms() const {
     return (max_sweep_time * 1000.0) / den;
 }
 
+void gc_stat::dump_info() const {
+    util::windows_code_page_manager wm;
+    wm.set_utf8_output();
+
+    using std::left;
+    using std::setw;
+    using std::setfill;
+    using std::setprecision;
+
+    const char* used_table_name[] = {
+        "object type",
+        "gc cycle",
+        "alloc count",
+        "object count",
+        "detail",
+        "time spend",
+        "gc time",
+        "avg time",
+        "max gc",
+        "max mark",
+        "max sweep"
+    };
+    const char* name[] = {
+        "string",
+        "vector",
+        "hashmap",
+        "function",
+        "upvalue",
+        "ghost",
+        "coroutine",
+        "namespace"
+    };
+
+    // calculate max indent length
+    usize indent = 0;
+    for (auto tname : used_table_name) {
+        auto len = strlen(tname);
+        indent = indent<len? len:indent;
+    }
+    for (auto n : name) {
+        auto len = strlen(n);
+        indent = indent<len? len:indent;
+    }
+    for(u32 i = 0; i < GC_TYPE_SIZE; ++i) {
+        auto len = std::to_string(gc_cycle_trigger_count[i]).length();
+        indent = indent<len? len:indent;
+        len = std::to_string(alloc_count[i]).length();
+        indent = indent<len? len:indent;
+        len = std::to_string(object_size[i]).length();
+        indent = indent<len? len:indent;
+    }
+
+    auto indent_string = std::string("──");
+    for(usize i = 0; i < indent; ++i) {
+        indent_string += "─";
+    }
+
+    const auto first_line = "╭" + indent_string + "┬" +
+                            indent_string + "┬" +
+                            indent_string + "┬" +
+                            indent_string + "╮";
+    const auto second_line = "├" + indent_string + "┼" +
+                             indent_string + "┼" +
+                             indent_string + "┼" +
+                             indent_string + "┤";
+    const auto mid_line = "├" + indent_string + "┼" +
+                          indent_string + "┴" +
+                          indent_string + "┴" +
+                          indent_string + "┤";
+    const auto another_mid_line = "├" + indent_string + "┼" +
+                                  indent_string + "─" +
+                                  indent_string + "─" +
+                                  indent_string + "┤";
+    const auto last_line = "╰" + indent_string + "┴" +
+                           indent_string + "─" +
+                           indent_string + "─" +
+                           indent_string + "╯";
+
+    std::clog << "\n" << first_line << "\n";
+    std::clog << "│ " << left << setw(indent) << setfill(' ') << "object type";
+    std::clog << " │ " << left << setw(indent) << setfill(' ') << "gc cycle";
+    std::clog << " │ " << left << setw(indent) << setfill(' ') << "alloc count";
+    std::clog << " │ " << left << setw(indent) << setfill(' ') << "object count";
+    std::clog << " │\n" << second_line << "\n" << std::internal;
+
+    for (u32 i = 0; i < GC_TYPE_SIZE; ++i) {
+        if (!gc_cycle_trigger_count[i] &&
+            !alloc_count[i] &&
+            !object_size[i]) {
+            continue;
+        }
+        std::clog << "│ " << left << setw(indent) << setfill(' ') << name[i];
+        std::clog << " │ " << left << setw(indent) << setfill(' ') << gc_cycle_trigger_count[i];
+        std::clog << " │ " << left << setw(indent) << setfill(' ') << alloc_count[i];
+        std::clog << " │ " << left << setw(indent) << setfill(' ') << object_size[i];
+        std::clog << " │\n" << std::internal;
+    }
+    std::clog << mid_line << "\n";
+
+    std::clog << "│ " << left << setw(indent) << setfill(' ') << "detail";
+    std::clog << " │ " << left << setw(indent) << setfill(' ') << "time spend";
+    std::clog << "   " << left << setw(indent) << setfill(' ') << " ";
+    std::clog << "   " << left << setw(indent) << setfill(' ') << " ";
+    std::clog << " │\n" << another_mid_line << "\n";
+
+    std::clog << "│ " << left << setw(indent) << setfill(' ') << "gc time";
+    std::clog << " │ " << setw(indent-3) << setprecision(4) << gc_time_ms() << " ms";
+    std::clog << setw(indent*2+7) << " " << "│\n";
+
+    std::clog << "│ " << left << setw(indent) << setfill(' ') << "avg time";
+    std::clog << " │ " << setw(indent-3) << setprecision(4) << avg_time_ms() << " ms";
+    std::clog << setw(indent*2+7) << " " << "│\n";
+
+    std::clog << "│ " << left << setw(indent) << setfill(' ') << "avg mark";
+    std::clog << " │ " << setw(indent-3) << setprecision(4) << avg_mark_time_ms() << " ms";
+    std::clog << setw(indent*2+7) << " " << "│\n";
+
+    std::clog << "│ " << left << setw(indent) << setfill(' ') << "avg sweep";
+    std::clog << " │ " << setw(indent-3) << setprecision(4) << avg_sweep_time_ms() << " ms";
+    std::clog << setw(indent*2+7) << " " << "│\n";
+
+    std::clog << "│ " << left << setw(indent) << setfill(' ') << "max mark";
+    std::clog << " │ " << setw(indent-3) << setprecision(4) << max_mark_time_ms() << " ms";
+    std::clog << setw(indent*2+7) << " " << "│\n";
+
+    std::clog << "│ " << left << setw(indent) << setfill(' ') << "max sweep";
+    std::clog << " │ " << setw(indent-3) << setprecision(4) << max_sweep_time_ms() << " ms";
+    std::clog << setw(indent*2+7) << " " << "│\n";
+
+    std::clog << last_line << "\n" << std::internal;
+
+    wm.restore_code_page();
+}
+
 }
\ No newline at end of file
diff --git a/src/util/gc_stat.h b/src/util/gc_stat.h
index ca0083e..7c7b420 100644
--- a/src/util/gc_stat.h
+++ b/src/util/gc_stat.h
@@ -19,8 +19,6 @@ struct gc_stat {
     i64 max_mark_time = 0;
     i64 max_sweep_time = 0;
 
-    bool flag_concurrent_mark_triggered = false;
-
     std::chrono::time_point<std::chrono::high_resolution_clock> start_time;
 
     void stamp() {
@@ -50,6 +48,8 @@ struct gc_stat {
     f64 avg_sweep_time_ms() const;
     f64 max_mark_time_ms() const;
     f64 max_sweep_time_ms() const;
+
+    void dump_info() const;
 };
 
 }
\ No newline at end of file