nodejs v8内存gc分配失败

Question

我正在尝试使用一个不做任何事情的服务器来分析nodejs v8内存。我使用node-memwatch来获取heap diff。我在连接之前和连接断开后收集堆信息。我使用node-memwatch。我尝试了200个来自客户端的并发连接。

这是断开连接后的gc跟踪。

有谁能帮我理解一下：

1.为什么内存在增加？在连接中断后，服务器绝对什么也不做。当垃圾被收集时，它不应该总是被丢弃吗？

1. 那些分配失败是什么？我如何真正解释这里的跟踪?

 15802 ms: Mark-sweep 8.9 (45.0) -> 8.1 (45.0) MB, 58 ms [allocation failure] [GC in old space forced by flags].
 16144 ms: Mark-sweep 9.2 (45.0) -> 8.4 (45.0) MB, 53 ms [allocation failure] [GC in old space forced by flags].
 16495 ms: Mark-sweep 9.5 (45.0) -> 8.7 (46.0) MB, 60 ms [allocation failure] [GC in old space forced by flags].
 16837 ms: Mark-sweep 9.8 (46.0) -> 9.0 (46.0) MB, 56 ms [allocation failure] [GC in old space forced by flags].
 17197 ms: Mark-sweep 10.1 (46.0) -> 9.4 (46.0) MB, 62 ms [allocation failure] [GC in old space forced by flags].
 17905 ms: Mark-sweep 11.5 (46.0) -> 10.0 (47.0) MB, 74 ms [Runtime::PerformGC] [GC in old space forced by flags].                                                               
 18596 ms: Mark-sweep 12.2 (47.0) -> 10.7 (47.0) MB, 75 ms [Runtime::PerformGC] [GC in old space forced by flags].
 19315 ms: Mark-sweep 12.8 (47.0) -> 11.3 (48.0) MB, 83 ms [allocation failure] [GC in old space forced by flags].
 20035 ms: Mark-sweep 13.4 (48.0) -> 12.0 (49.0) MB, 90 ms [Runtime::PerformGC] [GC in old space forced by flags].
 21487 ms: Mark-sweep 16.0 (49.0) -> 13.2 (50.0) MB, 96 ms [Runtime::PerformGC] [GC in old space forced by flags].
 22950 ms: Mark-sweep 17.3 (50.0) -> 14.5 (52.0) MB, 116 ms [Runtime::PerformGC] [GC in old space forced by flags].
 24376 ms: Mark-sweep 18.8 (52.0) -> 15.9 (53.0) MB, 114 ms [allocation failure] [GC in old space forced by flags].
 25849 ms: Mark-sweep 19.9 (53.0) -> 17.2 (54.0) MB, 129 ms [Runtime::PerformGC] [GC in old space forced by flags].
 28773 ms: Mark-sweep 25.2 (54.0) -> 19.7 (57.0) MB, 149 ms [allocation failure] [GC in old space forced by flags].
 31725 ms: Mark-sweep 27.7 (57.0) -> 22.2 (59.0) MB, 172 ms [Runtime::PerformGC] [GC in old space forced by flags].
 34678 ms: Mark-sweep 30.2 (59.0) -> 24.7 (61.0) MB, 190 ms [Runtime::PerformGC] [GC in old space forced by flags].
 44045 ms: Mark-sweep 28.4 (61.0) -> 25.8 (63.0) MB, 180 ms [idle notification] [GC in old space forced by flags].
 44216 ms: Mark-sweep 25.8 (63.0) -> 25.8 (63.0) MB, 170 ms [idle notification] [GC in old space requested].
 57471 ms: Mark-sweep 26.9 (63.0) -> 25.8 (62.0) MB, 167 ms [Runtime::PerformGC] [GC in old space forced by flags].
 57651 ms: Mark-sweep 26.8 (62.0) -> 25.5 (62.0) MB, 160 ms [Runtime::PerformGC] [GC in old space forced by flags].
 57828 ms: Mark-sweep 26.5 (62.0) -> 25.5 (62.0) MB, 159 ms [Runtime::PerformGC] [GC in old space forced by flags].

谢谢,

Answer 1

根据代码：

PrintF("%s %.1f (%.1f) -> %.1f (%.1f) MB, ",
       CollectorString(),
       static_cast<double>(start_object_size_) / MB,                                                                                    
       static_cast<double>(start_memory_size_) / MB, 
       SizeOfHeapObjects(),
       end_memory_size_mb);

每一行都是一个gc，当gc启动时，

start_object_size_ = heap_->SizeOfObjects();

在gc摘要中：

PrintF("total_size_before=%" V8_PTR_PREFIX "d ", start_object_size_);                                                                   
PrintF("total_size_after=%" V8_PTR_PREFIX "d ", heap_->SizeOfObjects());

至于为什么我的应用程序空闲时start_object_size_会增加，我猜可能是在gc期间，一些对象被提升到旧空间，并导致旧空间中的对象大小增加。

Answer 2

“分配失败”听起来非常戏剧性，但并不涉及真正的失败。这只是意味着我们分配了如此多的内存，现在是时候进行GC了，看看我们是否可以收集一些内存。

看起来您正在使用--gc-global标志("GC由标志强制执行“)运行。这对于生产来说不是一个好主意，尽管它可以在调试时缩小问题的范围。

我不知道你的进程为什么会泄露。您可能会发现堆分析器很有用。请参阅https://github.com/felixge/node-memory-leak-tutorial