Term explanation
procrank view process memory tool. There are four options, which are a bit vague. I checked it online and recorded it.
VSS-Virtual Set Size virtual memory consumption (including memory occupied by shared libraries)
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- RSS-Resident Set Size Actual physical memory used (including memory occupied by shared libraries)
- PSS-Proportional Set Size Actual physical memory (memory used by shared libraries)
- USS-Physical memory occupied by the Unique Set Size process alone (not including memory occupied by shared libraries)< /li>
Generally speaking, the memory footprint has the following rules: 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 4 096 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, ie 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 pro cesses. 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, ie 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.
The above explanation of these four words:
VSS: virtual memory size
RSS: Physical memory including the memory of all process shared libraries
PSS: Physical memory including the memory of some process shared libraries, and the memory size of some process shared libraries is shared The number of processes in the shared library is divided into equal proportions.
USS: The actual physical memory being used by this process.
Check the process memory space and process memory for leaks, just look at the USS.
# procrank
procrank PID 225K 108K 384K 225K 108K 254K Vss Pss Rss Uss cmdline 481 31536K 30936K 14337K 26128K 992 9956K 5126K 526K 526K 526K 5126K system_server 475 475 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 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