diff --git a/README.md b/README.md
index d763a863..89921e4b 100644
--- a/README.md
+++ b/README.md
@@ -1,7 +1,7 @@
 更多原创内容和干货分享：
 
 1. [公众号—JavaGuide](#公众号) ： 最新原创文章+免费领取本文档配套的《Java面试突击》以及Java工程师必备学习资源）
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+2. [微信](#联系我) ：如果需要和我交流的话可以加我私人微信(ps: 有问题的话也可以问，我会尽量回答大家，我很随和的，哈哈！另外，账号快加满了)
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diff --git a/docs/java/jvm/JVM垃圾回收.md b/docs/java/jvm/JVM垃圾回收.md
index 972e4267..ad4097c1 100644
--- a/docs/java/jvm/JVM垃圾回收.md
+++ b/docs/java/jvm/JVM垃圾回收.md
@@ -159,21 +159,24 @@ public class GCTest {
 > ```c++
 > uint ageTable::compute_tenuring_threshold(size_t survivor_capacity) {
 > 	//survivor_capacity是survivor空间的大小
->   size_t desired_survivor_size = (size_t)((((double) survivor_capacity)*TargetSurvivorRatio)/100);
->   size_t total = 0;
->   uint age = 1;
->   while (age < table_size) {
->     total += sizes[age];//sizes数组是每个年龄段对象大小
->     if (total > desired_survivor_size) break;
->     age++;
->   }
->   uint result = age < MaxTenuringThreshold ? age : MaxTenuringThreshold;
+> size_t desired_survivor_size = (size_t)((((double) survivor_capacity)*TargetSurvivorRatio)/100);
+> size_t total = 0;
+> uint age = 1;
+> while (age < table_size) {
+>  total += sizes[age];//sizes数组是每个年龄段对象大小
+>  if (total > desired_survivor_size) break;
+>  age++;
+> }
+> uint result = age < MaxTenuringThreshold ? age : MaxTenuringThreshold;
 > 	...
 > }
 > 
 > ```
 >
-> 
+> 额外补充说明([issue672](https://github.com/Snailclimb/JavaGuide/issues/672))：**关于默认的晋升年龄是15，这个说法的来源大部分都是《深入理解Java虚拟机》这本书。**
+> 如果你去Oracle的官网阅读[相关的虚拟机参数](https://docs.oracle.com/javase/8/docs/technotes/tools/unix/java.html)，你会发现`-XX:MaxTenuringThreshold=threshold`这里有个说明
+>
+> **Sets the maximum tenuring threshold for use in adaptive GC sizing. The largest value is 15. The default value is 15 for the parallel (throughput) collector, and 6 for the CMS collector.默认晋升年龄并不都是15，这个是要区分垃圾收集器的，CMS就是6.**
 
 
 ## 2 对象已经死亡？