GC_FOR_ALLOC更“严重”吗？在调查内存使用情况时？ [英] Is GC_FOR_ALLOC more "serious" when investigating memory usage?

问题描述

我目前正在用我的Android应用程序调查垃圾收集问题，我很想知道GC_FOR_ALLOC是否指示比其他GC消息（如GC_CONCURRENT）更大的问题。

据我了解，GC_CONCURRENT正在做垃圾回收器应该做的事情。堆已经达到了一个特定的限制，最好去清理内存。

GC_FOR_ALLOC向我建议更严重的事情发生，如果我试图创建一个对象，并且没有内存留下来做。

GC消息有优先级或严重性级别吗？

GC_FOR_ALLOC 比 GC_CONCURRENT 更严重，因为 GC_FOR_ALLOC 意味着没有足够的可用内存来完成分配请求，所以需要垃圾回收，而 GC_CONCURRENT 只是意味着GC感觉就像跑步一样，通常是因为分配后可用内存的数量低于某个阈值。

A GC_FOR_ALLOC 本身并不是您的应用程序中存在问题的标志：



• Android应用程序以一个小堆增长在某种程度上）当应用离子需要越来越多的内存，并且在增加堆的大小之前完成 GC_FOR_ALLOC 。在这种情况下， GC_FOR_ALLOC 是完全正常的。


• 如果分配内存的速度比并发GC有时间释放内存更快， c $ c> GC_FOR_ALLOC 是不可避免的。而且分配内存的速度比并发GC可以释放内存的速度更快。

Android上更严重的GC类型是 GC_BEFORE_OOM ，当分配请求在 GC_FOR_ALLOC 之后失败并且应用程序堆增长得如此大被允许。当发生这种情况时，作为最后的手段，Dalvik将尝试释放SoftReferences，然后再进行最后的内存分配尝试，并且该失败将抛出OutOfMemory异常。

如果你想看看这个逻辑的代码，它在 tryMalloc（）中。 p =平台/ dalvik.git; A =斑点; F = VM /分配/ Heap.cpp; H = 9eee817e5e5cc1115041c5548214292a7f6e1090; HB = HEAD> dalvik.git / VM /分配/ Heap.cpp

无论如何，如果您不介意，我怀疑查看logcat输出是调试垃圾回收问题的最有效方法。我不知道你有什么具体问题，但是你有没有看过DDMS中的Allocation Tracker等工具，并借助 hprof-conv 来分析堆转储。工具？ （请参阅 http://android-developers.blogspot.se/2011/03/内存分析为android.html 例如开始。）

I'm currently investigating garbage collection problems with my Android app, and I'm curious to know if GC_FOR_ALLOC is indicative of a bigger problem than other GC messages, such as GC_CONCURRENT.

From my understanding, GC_CONCURRENT is doing what the garbage collector should do. The heap has reached a particular limit, better go clean up memory.

GC_FOR_ALLOC suggests to me something more serious is happening if I'm trying to create an object and there's no memory left to do it.

Is there a priority or "seriousness" level for the GC messages?

解决方案

In a sense, GC_FOR_ALLOC is more serious than GC_CONCURRENT, because GC_FOR_ALLOC means there were not enough free memory to fulfill an allocation request, so a garbage collection was necessary, whereas GC_CONCURRENT just means that the GC felt like running, typically because the amount of free memory became lower than a certain threshold after an allocation.

A GC_FOR_ALLOC is by itself not a sign of a problem in your application however:

• Android applications start with a small heap which grows (up to a point) when applications require more and more memory, and a GC_FOR_ALLOC is done before increasing the size of the heap. In this case GC_FOR_ALLOC is perfectly normal.
• If you allocate memory faster than the concurrent GC has time to free it up, GC_FOR_ALLOC is inevitable. And there's nothing inherently wrong with allocating memory faster than the concurrent GC can free up memory.

A more serious type of GC on Android is GC_BEFORE_OOM, which is performed when an allocation request fails even after GC_FOR_ALLOC and when the application heap has grown as big as it is allowed to be. When this happen, as a last resort, Dalvik will try to release SoftReferences as well, before doing a final attempt at allocating memory and if that fails throw an OutOfMemory exception.

If you're curious to look at the code for this logic, it is in tryMalloc() in dalvik.git/vm/alloc/Heap.cpp

Anyway, if you don't mind, I doubt that looking at logcat output is the most efficient way to debug your garbage collection problems. I don't know what specific problem you are having, but have you looked into tools such as the Allocation Tracker in DDMS and analyzing heap dumps with the help of the hprof-conv tool? (See http://android-developers.blogspot.se/2011/03/memory-analysis-for-android.html for example to get started.)

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