Android内存之VSS/RSS/PSS/USS

Android内存之VSS/RSS/PSS/USS

Terms

VSS - Virtual Set Size 虚拟耗用内存（包含共享库占用的内存）

RSS - Resident Set Size 实际使用物理内存（包含共享库占用的内存）

PSS - Proportional Set Size 实际使用的物理内存（比例分配共享库占用的内存）

USS - Unique Set Size 进程独自占用的物理内存（不包含共享库占用的内存）

一般来说内存占用大小有如下规律：VSS >= RSS >= PSS >= USS

Overview

The aim of this post is to provide information that will assist in interpreting memory reports from various tools so the true memory usage for Linux processes and the system can be determined.

Android has a tool called procrank (/system/xbin/procrank), which lists out the memory usage of Linux processes in order from highest to lowest usage. The sizes reported per process are VSS, RSS, PSS, and USS.For the sake of simplicity in this description,
memory will be expressed in terms of pages, rather than bytes. Linux systems like ours manage memory in 4096 byte pages at the lowest level.

VSS (reported as VSZ from ps)

is the total accessible address space of a process. This size also includes memory that may not be resident in RAM like mallocs that have been allocated but not written to. VSS is of very little use for determing real
memory usage of a process.

RSS

is the total memory actually held in RAM for a process. RSS can be misleading, because it reports the total all of the shared libraries that the process uses, even though a shared library
is only loaded into memory once regardless of how many processes use it. RSS is not an accurate representation of the memory usage for a single process.

PSS

differs from RSS in that it reports the proportional size of its shared libraries, i.e. if three processes all use a shared library that has 30 pages, that library will only contribute 10 pages to the PSS that is reported
for each of the three processes. PSS is a very useful number because when the PSS for all processes in the system are summed together, that is a good representation for the total memory usage in the system. When a process is killed, the shared libraries that
contributed to its PSS will be proportionally distributed to the PSS totals for the remaining processes still using that library. In this way PSS can be slightly misleading, because when a process is killed, PSS does not accurately represent the memory returned
to the overall system.

USS

is the total private memory for a process, i.e. that memory that is completely unique to that process. USS is an extremely useful number because it indicates the true incremental cost of running a particular process.
When a process is killed, the USS is the total memory that is actually returned to the system. USS is the best number to watch when initially suspicious of memory leaks in a process.

For systems that have Python available, there is also a nice tool called smem that will report memory statistics including all of these categories.

# procrank

procrank

PID Vss Rss Pss Uss cmdline

481 31536K 30936K 14337K 9956K system_server

475 26128K 26128K 10046K 5992K zygote

526 25108K 25108K 9225K 5384K android.process.acore

523 22388K 22388K 7166K 3432K com.android.phone

574 21632K 21632K 6109K 2468K com.android.settings

521 20816K 20816K 6050K 2776K jp.co.omronsoft.openwnn

474 3304K 3304K 1097K 624K /system/bin/mediaserver

37 304K 304K 289K 288K /sbin/adbd

29 720K 720K 261K 212K /system/bin/rild

601 412K 412K 225K 216K procrank

1 204K 204K 185K 184K /init

35 388K 388K 182K 172K /system/bin/qemud

284 384K 384K 160K 148K top

27 376K 376K 148K 136K /system/bin/vold

261 332K 332K 123K 112K logcat

33 396K 396K 105K 80K /system/bin/keystore

32 316K 316K 100K 88K /system/bin/installd

269 328K 328K 95K 72K /system/bin/sh

26 280K 280K 93K 84K /system/bin/servicemanager

45 304K 304K 91K 80K /system/bin/qemu-props

34 324K 324K 91K 68K /system/bin/sh

260 324K 324K 91K 68K /system/bin/sh

600 324K 324K 91K 68K /system/bin/sh

25 308K 308K 88K 68K /system/bin/sh

28 232K 232K 67K 60K /system/bin/debuggerd

转自：http://hubingforever.blog.163.com/blog/static/17104057920114411313717/