Android MemInfo 各项的意义（转）

我不是女神ヾ 2022-08-12 03:00 240阅读 0赞

可以使用adb shell dumpsys meminfo -a <process id>/<process name>来查看一个进程的memory。

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Naitve Heap Size: 从mallinfo usmblks获得，代表最大总共分配空间

Native Heap Alloc: 从mallinfo uorblks获得，总共分配空间

Native Heap Free: 从mallinfo fordblks获得，代表总共剩余空间

Native Heap Size 约等于Native Heap Alloc + Native Heap Free

mallinfo是一个C库， mallinfo 函数提供了各种各样的通过C的malloc（）函数分配的内存的统计信息。

Dalvik Heap Size:从Runtime totalMemory()获得，Dalvik Heap总共的内存大小。

Dalvik Heap Alloc: Runtime totalMemory()-freeMemory() ，Dalvik Heap分配的内存大小。

Dalvik Heap Free:从Runtime freeMemory()获得，Dalvik Heap剩余的内存大小。

Dalvik Heap Size 约等于Dalvik  Heap Alloc + Dalvik  Heap Free

OtherPss, include Cursor,Ashmem, Other Dev, .so mmap, .jar mmap, .apk mmap, .ttf mmap, .dex mmap, Other mmap, Unkown统计信息都可以在process的smap文件看到。

Objects and SQL 信息都是从Android Debug信息中获得。

其他类型               smap 路径名称          描述

Cursor                  /dev/ashmem/Cursor  Cursor消耗的内存(KB)

Ashmem               /dev/ashmem            匿名共享内存用来提供共享内存通过分配一个多个进程

可以共享的带名称的内存块

Other dev             /dev/                        内部driver占用的在 “Other dev”

.so mmap             .so                            C 库代码占用的内存

.jar mmap            .jar                           Java 文件代码占用的内存

.apk mmap           .apk                           apk代码占用的内存

.ttf mmap              .ttf                           ttf 文件代码占用的内存

.dex mmap             .dex                         Dex 文件代码占用的内存

Other mmap                                          其他文件占用的内存

But as to what the difference is between "Pss", "PrivateDirty", and "SharedDirty"... well now the fun begins.

A lot of memory in Android (and Linux systems in general) is actually shared across multiple processes. So how much memory a processes uses is really not clear. Add on top of that paging out to disk (let alone swap which we don't use on Android) and it is even less clear.

Thus if you were to take all of the physical RAM actually mapped in to each process, and add up all of the processes, you would probably end up with a number much greater than the actual total RAM.

The Pss number is a metric the kernel computes that takes into account memory sharing -- basically each page of RAM in a process is scaled by a ratio of the number of other processes also using that page. This way you can (in theory) add up the pss across all processes to see the total RAM they are using, and compare pss between processes to get a rough idea of their relative weight.

The other interesting metric here is PrivateDirty, which is basically the amount of RAM inside the process that can not be paged to disk (it is not backed by the same data on disk), and is not shared with any other processes. Another way to look at this is the RAM that will become available to the system when that process goes away (and probably quickly subsumed into caches and other uses of it).

That is pretty much the SDK APIs for this. However there is more you can do as a developer with your device.

Using adb, there is a lot of information you can get about the memory use of a running system. A common one is the command "adb shell dumpsys meminfo" which will spit out a bunch of information about the memory use of each Java process, containing the above info as well as a variety of other things. You can also tack on the name or pid of a single process to see, for example "adb shell dumpsys meminfo system" give me the system process:

** MEMINFO in pid 890 [system] **
                        native   dalvik    other    total
                size:    10940     7047      N/A    17987
           allocated:     8943     5516      N/A    14459
                free:      336     1531      N/A     1867
               (Pss):     4585     9282    11916    25783
      (shared dirty):     2184     3596      916     6696
        (priv dirty):     4504     5956     7456    17916
    
     Objects
               Views:      149        ViewRoots:        4
         AppContexts:       13       Activities:        0
              Assets:        4    AssetManagers:        4
       Local Binders:      141    Proxy Binders:      158
    Death Recipients:       49
     OpenSSL Sockets:        0
    
     SQL
                heap:      205          dbFiles:        0
           numPagers:        0   inactivePageKB:        0
        activePageKB:        0

The top section is the main one, where "size" is the total size in address space of a particular heap, "allocated" is the kb of actual allocations that heap thinks it has, "free" is the remaining kb free the heap has for additional allocations, and "pss" and "priv dirty" are the same as discussed before specific to pages associated with each of the heaps.

If you just want to look at memory usage across all processes, you can use the command "adb shell procrank". Output of this on the same system looks like:

PID      Vss      Rss      Pss      Uss  cmdline
      890   84456K   48668K   25850K   21284K  system_server
     1231   50748K   39088K   17587K   13792K  com.android.launcher2
      947   34488K   28528K   10834K    9308K  com.android.wallpaper
      987   26964K   26956K    8751K    7308K  com.google.process.gapps
      954   24300K   24296K    6249K    4824K  com.android.phone
      948   23020K   23016K    5864K    4748K  com.android.inputmethod.latin
      888   25728K   25724K    5774K    3668K  zygote
      977   24100K   24096K    5667K    4340K  android.process.acore
    ...
       59     336K     332K      99K      92K  /system/bin/installd
       60     396K     392K      93K      84K  /system/bin/keystore
       51     280K     276K      74K      68K  /system/bin/servicemanager
       54     256K     252K      69K      64K  /system/bin/debuggerd

Here the Vss and Rss columns are basically noise (these are the straight-forward address space and RAM usage of a process, where if you add up the RAM usage across processes you get an ridiculously large number).

Pss is as we've seen before, and Uss is Priv Dirty.

Interesting thing to note here: Pss and Uss are slightly (or more than slightly) different than what we saw in meminfo. Why is that? Well procrank uses a different kernel mechanism to collect its data than meminfo does, and they give slightly different results. Why is that? Honestly I haven't a clue. I believe procrank may be the more accurate one... but really, this just leave the point: "take any memory info you get with a grain of salt; often a very large grain."

Finally there is the command "adb shell cat /proc/meminfo" that gives a summary of the overall memory usage of the system. There is a lot of data here, only the first few numbers worth discussing (and the remaining ones understood by few people, and my questions of those few people about them often resulting in conflicting explanations):

MemTotal:         395144 kB
    MemFree:          184936 kB
    Buffers:             880 kB
    Cached:            84104 kB
    SwapCached:            0 kB

MemTotal is the total amount of memory available to the kernel and user space (often less than the actual physical RAM of the device, since some of that RAM is needed for the radio, DMA buffers, etc).

MemFree is the amount of RAM that is not being used at all. The number you see here is very high; typically on an Android system this would be only a few MB, since we try to use available memory to keep processes running

Cached is the RAM being used for filesystem caches and other such things. Typical systems will need to have 20MB or so for this to avoid getting into bad paging states; the Android out of memory killer is tuned for a particular system to make sure that background processes are killed before the cached RAM is consumed too much by them to result in such paging.

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