几个月之前看过一遍，结果过一阵子在查bitmap造成内存泄露时又感觉忘得差不多了，不晓得android os RAM 到底怎么分配的了。干脆，再翻翻，翻译翻译。（粗翻，不对请指出）
https://developer.android.com/studio/profile/investigate-ram.html?
观察所有的内存分配
为了更深入的研究，你需要下面这个指令来观察，你app的内存在不同类型的RAM分配之下是如何分开使用的：
adb shell dumpsys meminfo[-d]
加入-d 标识可以打印更多关于Dalvik 和 ART的内存使用信息。
这条命令的输出展示了app所有当前的内存分配，kb为单位。
当查看这些信息时，你需要知道下面几种分配类型：（之所以把英文也贴到文章结尾，是因为貌似这一块貌似更新过，几个月之前我看的分配类型好像不是这些，贴出英文，怕后期google有更新，好有一个对比）
私有RAM(分为Clean和Dirty)
这一部分内存是被你的进程独占的。当你的app进程销毁，这部分内存绝大多数会被系统收回。通常，私有RAM里面最重要的部分是私有dirty RAM,因为他不仅由你的进程独占，同时其所有内容也只能在RAM里面，不能被分页存入外存（因为android没有虚拟内存？），所以他尤其珍贵。所有Dalvik和native heap使用的内存都是私有dirty RAM 。你和Zygote 进程共享的Dalvik与native内存属于 共享dirty RAM。
个人理解:内存分
Private RAM (Dirty :上面已讲 Clean:不明？)
Shared RAM（Dirty：上面已讲 Clean:不明？）
PSS-实际使用的物理内存（比例分配共享库占用的内存）
这是一种把你的app所有有共享部分的进程内存也计算在内的测量手段。所有你的进程独占的RAM内存首先会直接计入PSS,然后与其他进程共享的内存会只计算共享的那一部分。例如，一块内存被2个进程共享，就会把这块内存的一半分别算入两个进程的PSS 里面去。
PSS这一测量规则的一个好处是你可以把所有的内存的PSS加在一起，就可以看到所有进程的实际使用总内存。这意味着PSS是一个很好的,测量一个进程实际使用内存的方法，同时也很方便与其他进程的内存使用量进行对比，而且方便计算总的可用内存。 例如：... （见链接图表）
通常，只需要关心 Pss Total和 Private Dirty 这两列，在一些例子中，Private Clean和Heap Alloc 列也有一些有趣的数据。为了观察更多的内存分配信息，你需要关注下面的数据:
Dalvik Heap:
Dalvik虚拟机所使用的那一部分RAM. PSS Total包含所有Zygote分配的内存（按所有共享进程的占比计入，上文对PSS的定义已经说过）The Private Dirty number is the actual RAM committed to only your app’s heap, composed of your own allocations and any Zygote allocation pages that have been modified since forking your app’s process from Zygote.(有些没看懂，Private Dirty是 真实的RAM内存，只属于app堆中，当app进程从zygote进程fork出来后，app所分配的和zygote所分配的内存就会发生改变？)
.so mmapand.dex mmap:
.oat mmap:
... Please stay tuned
View overall memory allocations
For further analysis, you might want to observe how your app's memory is divided between different types of RAM allocation with the followingadbcommand:
adb shell dumpsys meminfo [-d]
The -d flag prints more info related to Dalvik and ART memory usage.
The output lists all of your app's current allocations, measured in kilobytes.
When inspecting this information, you should be familiar with the following types of allocation:
Private (Clean and Dirty) RAM
This is memory that is being used by only your process. This is the bulk of the RAM that the system can reclaim when your app’s process is destroyed. Generally, the most important portion of this isprivate dirtyRAM, which is the most expensive because it is used by only your process and its contents exist only in RAM so can’t be paged to storage (because Android does not use swap). All Dalvik and native heap allocations you make will be private dirty RAM; Dalvik and native allocations you share with the Zygote process are shared dirty RAM.
Proportional Set Size (PSS)
This is a measurement of your app’s RAM use that takes into account sharing pages across processes. Any RAM pages that are unique to your process directly contribute to its PSS value, while pages that are shared with other processes contribute to the PSS value only in proportion to the amount of sharing. For example, a page that is shared between two processes will contribute half of its size to the PSS of each process.
A nice characteristic of the PSS measurement is that you can add up the PSS across all processes to determine the actual memory being used by all processes. This means PSS is a good measure for the actual RAM weight of a process and for comparison against the RAM use of other processes and the total available RAM.
For example, below is the the output for Map’s process on a Nexus 5 device. There is a lot of information here, but key points for discussion are listed below.
adb shell dumpsys meminfo com.google.android.apps.maps -d
Note:The information you see might vary slightly from what is shown here, because some details of the output differ across platform versions.
** MEMINFO in pid 18227 [com.google.android.apps.maps] **
Pss Private Private Swapped Heap Heap Heap
Total Dirty Clean Dirty Size Alloc Free
------ ------ ------ ------ ------ ------ ------
Native Heap 10468 10408 0 0 20480 14462 6017
Dalvik Heap 34340 33816 0 0 62436 53883 8553
Dalvik Other 972 972 0 0
Stack 1144 1144 0 0
Gfx dev 35300 35300 0 0
Other dev 5 0 4 0
.so mmap 1943 504 188 0
.apk mmap 598 0 136 0
.ttf mmap 134 0 68 0
.dex mmap 3908 0 3904 0
.oat mmap 1344 0 56 0
.art mmap 2037 1784 28 0
Other mmap 30 4 0 0
EGL mtrack 73072 73072 0 0
GL mtrack 51044 51044 0 0
Unknown 185 184 0 0
TOTAL 216524 208232 4384 0 82916 68345 14570
Dalvik Details
.Heap 6568 6568 0 0
.LOS 24771 24404 0 0
.GC 500 500 0 0
.JITCache 428 428 0 0
.Zygote 1093 936 0 0
.NonMoving 1908 1908 0 0
.IndirectRef 44 44 0 0
Objects
Views: 90 ViewRootImpl: 1
AppContexts: 4 Activities: 1
Assets: 2 AssetManagers: 2
Local Binders: 21 Proxy Binders: 28
Parcel memory: 18 Parcel count: 74
Death Recipients: 2 OpenSSL Sockets: 2
Here is an older dumpsys on Dalvik of the gmail app:
** MEMINFO in pid 9953 [com.google.android.gm] **
Pss Pss Shared Private Shared Private Heap Heap Heap
Total Clean Dirty Dirty Clean Clean Size Alloc Free
------ ------ ------ ------ ------ ------ ------ ------ ------
Native Heap 0 0 0 0 0 0 7800 7637(6) 126
Dalvik Heap 5110(3) 0 4136 4988(3) 0 0 9168 8958(6) 210
Dalvik Other 2850 0 2684 2772 0 0
Stack 36 0 8 36 0 0
Cursor 136 0 0 136 0 0
Ashmem 12 0 28 0 0 0
Other dev 380 0 24 376 0 4
.so mmap 5443(5) 1996 2584 2664(5) 5788 1996(5)
.apk mmap 235 32 0 0 1252 32
.ttf mmap 36 12 0 0 88 12
.dex mmap 3019(5) 2148 0 0 8936 2148(5)
Other mmap 107 0 8 8 324 68
Unknown 6994(4) 0 252 6992(4) 0 0
TOTAL 24358(1) 4188 9724 17972(2)16388 4260(2)16968 16595 336
Objects
Views: 426 ViewRootImpl: 3(8)
AppContexts: 6(7) Activities: 2(7)
Assets: 2 AssetManagers: 2
Local Binders: 64 Proxy Binders: 34
Death Recipients: 0
OpenSSL Sockets: 1
SQL
MEMORY_USED: 1739
PAGECACHE_OVERFLOW: 1164 MALLOC_SIZE: 62
In general, be concerned with only thePss TotalandPrivate Dirtycolumns. In some cases, thePrivate CleanandHeap Alloccolumns also offer interesting data. More information about the different memory allocations (the rows) you should observe follows:
Dalvik Heap
The RAM used by Dalvik allocations in your app. ThePss Totalincludes all Zygote allocations (weighted by their sharing across processes, as described in the PSS definition above). ThePrivate Dirtynumber is the actual RAM committed to only your app’s heap, composed of your own allocations and any Zygote allocation pages that have been modified since forking your app’s process from Zygote.
Note:On newer platform versions that have theDalvik Othersection, thePss TotalandPrivate Dirtynumbers for Dalvik Heap do not include Dalvik overhead such as the just-in-time compilation (JIT) and GC bookkeeping, whereas older versions list it all combined underDalvik.
TheHeap Allocis the amount of memory that the Dalvik and native heap allocators keep track of for your app. This value is larger thanPss TotalandPrivate Dirtybecause your process was forked from Zygote and it includes allocations that your process shares with all the others.
.so mmapand.dex mmap
The RAM being used for mapped.so(native) and.dex(Dalvik or ART) code. ThePss Totalnumber includes platform code shared across apps; thePrivate Cleanis your app’s own code. Generally, the actual mapped size will be much larger—the RAM here is only what currently needs to be in RAM for code that has been executed by the app. However, the .so mmap has a large private dirty, which is due to fix-ups to the native code when it was loaded into its final address.
.oat mmap
This is the amount of RAM used by the code image which is based off of the preloaded classes which are commonly used by multiple apps. This image is shared across all apps and is unaffected by particular apps.
.art mmap
This is the amount of RAM used by the heap image which is based off of the preloaded classes which are commonly used by multiple apps. This image is shared across all apps and is unaffected by particular apps. Even though the ART image containsObjectinstances, it does not count towards your heap size.
.Heap(only with -d flag)
This is the amount of heap memory for your app. This excludes objects in the image and large object spaces, but includes the zygote space and non-moving space.
.LOS(only with -d flag)
This is the amount of RAM used by the ART large object space. This includes zygote large objects. Large objects are all primitive array allocations larger than 12KB.
.GC(only with -d flag)
This is the amount of internal GC accounting overhead for your app. There is not really any way to reduce this overhead.
.JITCache(only with -d flag)
This is the amount of memory used by the JIT data and code caches. Typically, this is zero since all of the apps will be compiled at installed time.
.Zygote(only with -d flag)
This is the amount of memory used by the zygote space. The zygote space is created during device startup and is never allocated into.
.NonMoving(only with -d flag)
This is the amount of RAM used by the ART non-moving space. The non-moving space contains special non-movable objects such as fields and methods. You can reduce this section by using fewer fields and methods in your app.
.IndirectRef(only with -d flag)
This is the amount of RAM used by the ART indirect reference tables. Usually this amount is small, but if it is too high, it might be possible to reduce it by reducing the number of local and global JNI references used.
Unknown
Any RAM pages that the system could not classify into one of the other more specific items. Currently, this contains mostly native allocations, which cannot be identified by the tool when collecting this data due to Address Space Layout Randomization (ASLR). Like the Dalvik heap, thePss Totalfor Unknown takes into account sharing with Zygote, andPrivate Dirtyis unknown RAM dedicated to only your app.
TOTAL
The total Proportional Set Size (PSS) RAM used by your process. This is the sum of all PSS fields above it. It indicates the overall memory weight of your process, which can be directly compared with other processes and the total available RAM.
ThePrivate DirtyandPrivate Cleanare the total allocations within your process, which are not shared with other processes. Together (especiallyPrivate Dirty), this is the amount of RAM that will be released back to the system when your process is destroyed. Dirty RAM is pages that have been modified and so must stay committed to RAM (because there is no swap); clean RAM is pages that have been mapped from a persistent file (such as code being executed) and so can be paged out if not used for a while.
ViewRootImpl
The number of root views that are active in your process. Each root view is associated with a window, so this can help you identify memory leaks involving dialogs or other windows.
AppContextsandActivities
The number of appContextandActivityobjects that currently live in your process. This can help you to quickly identify leakedActivityobjects that can’t be garbage collected due to static references on them, which is common. These objects often have many other allocations associated with them, which makes them a good way to track large memory leaks.
Note:AVieworDrawableobject also holds a reference to theActivitythat it's from, so holding aVieworDrawableobject can also lead to your app leaking anActivity.
Trigger memory leaks
While using the tools described above, you should aggressively stress your app code and try forcing memory leaks. One way to provoke memory leaks in your app is to let it run for a while before inspecting the heap. Leaks will trickle up to the top of the allocations in the heap. However, the smaller the leak, the longer you need to run the app in order to see it.
You can also trigger a memory leak in one of the following ways:
Rotate the device from portrait to landscape and back again multiple times while in different activity states. Rotating the device can often cause an app to leak anActivity,Context, orViewobject because the system recreates theActivityand if your app holds a reference to one of those objects somewhere else, the system can't garbage collect it.
Switch between your app and another app while in different activity states (navigate to the Home screen, then return to your app).
Tip:You can also perform the above steps by using themonkeytest framework. For more information on running the monkey test framework, read themonkeyrunnerdocumentation.
