Android内存使用——垃圾回收LOG，GC_CONCURRENT等的意义的说明

在调试程序的时候，经常发现GC_CONCURRENT之类的打印。在网上搜了一下，感觉说法各式各样。最后，在Google的官方网站上发现了详细介绍。

Every time a garbage collection occurs, logcat prints a message with the following information:

D/dalvikvm: <GC_Reason> <Amount_freed>, <Heap_stats>, <External_memory_stats>, <Pause_time>

GC Reason

What triggered the garbage collection and what kind of collection it is. Reasons that may appearinclude:

GC_CONCURRENT

A concurrent garbage collection that frees up memory as your heap begins to fill up.

GC_FOR_MALLOC

A garbage collection caused because your app attempted to allocate memory when your heap wasalready full, so the system had to stop your app and reclaim memory.

GC_HPROF_DUMP_HEAP

A garbage collection that occurs when you create an HPROF file to analyze your heap.

GC_EXPLICIT

An explicit garbage collection, such as when you call gc() (which youshould avoid calling and instead trust the garbage collector to run when needed).

GC_EXTERNAL_ALLOC

This happens only on API level 10 and lower (newer versions allocate everything in the Dalvikheap). A garbage collection for externally allocated memory (such as the pixel data stored innative memory or NIO byte buffers).

Amount freed

The amount of memory reclaimed from this garbage collection.

Heap stats

Percentage free and (number of live objects)/(total heap size).

External memory stats

Externally allocated memory on API level 10 and lower (amount of allocated memory) / (limit atwhich collection will occur).

Pause time

Larger heaps will have larger pause times. Concurrent pause times show two pauses: one at thebeginning of the collection and another near the end.

For example:

D/dalvikvm( 9050): GC_CONCURRENT freed 2049K, 65% free 3571K/9991K, external 4703K/5261K, paused 2ms+2ms

来源： <http://developer.android.com/tools/debugging/debugging-memory.html#LogMessages>

 

GC Reason：引起GC回收的原因。包括a)GC_CONCURRENT：我的理解是当你的堆快被用完的时候，就会触发这个GC回收。b)堆已经满了，同时又要试图分配新的内存，所以系统要回收内存。c）GC_HPROF_DUMP_HEAP这是做HPROF分析用的，正常情况下不会有的。d）这个是明确调用gc产出的垃圾回收。e）GC_EXTERNAL_ALLOC这个在2.3版本以后已经废弃了。所以不用关心了。

Amount freed：本次垃圾回收释放出来的内存。

Heap stats：当前空闲内存占总内存的百分比。比如下面的例子总的65%就是说有65%的空闲。二后面的3571K是占用了这么多，9991K是总的内存。这两个值相除，就是占用的百分比，加上前面的65%正好是100%。

External memory stats：2.3之后就废弃了。

Pause time：你的应用暂停的时间。

假如3571K/9991K 这个值不断增加，从来不减少，则可能有内存泄漏的问题。

 

来自为知笔记(Wiz)