What is rss in linux

In Linux, the full name of rss is "Resident Set Size", which refers to the resident memory set, indicating the actual physical memory size occupied by the corresponding process in RAM, and does not include the virtual memory occupied in SWAP. RSS does not include the memory that goes into the swap partition, but does include the memory occupied by shared libraries (as long as the shared libraries are in memory).

#The operating environment of this tutorial: CentOS 6 system, Dell G3 computer.

In Linux memory management, whether it is the top command or the ps command, there will be two terms RSS and VSZ. Example:

[root@localhost ~]# ps aux
#查看系统中所有的进程
USER PID %CPU %MEM  VSZ  RSS   TTY STAT START TIME COMMAND
root   1  0.0  0.2 2872 1416   ?   Ss   Jun04 0:02 /sbin/init
root   2  0.0  0.0    0    0   ?    S   Jun04 0:00 [kthreadd]
root   3  0.0  0.0    0    0   ?    S   Jun04 0:00 [migration/0]
root   4  0.0  0.0    0    0   ?    S   Jun04 0:00 [ksoftirqd/0]
…省略部分输出…

Here we will take you to learn about RSS and VSZ.

linux RSS

RSS is the resident set size (Resident Set Size), which indicates the actual physical memory size occupied by the corresponding process in RAM and is not included in SWAP The virtual memory occupied in . Even the memory size in memory using shared libraries is included in the calculation, including the complete memory in the stack and heap.

• RSS does not include memory going into the swap partition.

• RSS includes the memory occupied by the shared library (as long as the shared library is in memory)

• RSS includes all allocated stack memory and heap memory.

linux VSZ

VSZ (Virtual Memory Size), indicating the virtual memory size, indicating all the memory that the process can access, including Swap memory and shared library memory.

VSZ includes all memory that the process can access, including what goes into the swap partition, and the memory occupied by shared libraries.

Example:

If the binary file size of process A is 500KB, and it is linked to a 2500KB shared library and has a stack/heap size of 200KB, this Another 100KB of the 200KB is in memory, 100KB is in SWAP space, and 1000KB of shared libraries and 400KB of its own binaries are loaded. Then

RSS:

400K + 1000K + 100K = 1500K

VSZ

500K + 2500K + 200K = 3200K

Part of the RSS comes from the shared library, and the shared library may be used by many processes, so if the RSS of all processes are added up , may be larger than system memory.

There is a newer parameter PSS (proportional set size), which calculates shared memory differently from RSS. Referring to the previous example, if two processes use the same shared library, then:

PSS:

400K (1000K/2) 100K = 400K 500K 100K = 1000K

Threads share the same address space, so all threads within a process have the same RSS, VSZ and PSS. You can use the ps or top command to observe this information.

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