pmap - Process Memory Map

Linux Tutorials - Herong's Tutorial Examples

∟pmap - Process Memory Map

This section provides a tutorial on how to install 'smem' and use it to report memory usage of each running process.

What Is "pmap"? - "pmap" is a Linux command that reports the virtual memory map of a given process. Here are some examples of "pmap" command output:

1. Report virtual memory map for process ID 1998.

herong$ sudo pmap 1998

1998:   /usr/libexec/mysqld --basedir=/usr
0000561c0ddea000  60468K r-x-- mysqld
0000561c118f7000   1492K r---- mysqld
0000561c11a6c000   3612K rw--- mysqld
0000561c11df3000   5300K rw---   [ anon ]
0000561c1403c000  79032K rw---   [ anon ]
00007ff90ac25000     24K r-x-- libevent_openssl-2.1.so.6.0.2
00007ff90ac2b000   2044K ----- libevent_openssl-2.1.so.6.0.2
00007ff90ae2a000      4K r---- libevent_openssl-2.1.so.6.0.2
00007ff90ae2b000      4K rw---   [ anon ]
...

 total          3439672K

The output shows that:

The program code "mysqld (/usr/libexec/mysqld)" is distributed in 3 locations in the virtual memory.
The data area is reported as "[ anon ] (anonymous mapping)" and scattered in multiple locations.
Libraries (linked exclusively to the process and share with other processes) are also reported. libevent_openssl-2.1.so.6.0.2 is an example.

2. Report virtual memory map in the extended format, which provides 2 extra output fields and field headers.

herong$ sudo pmap -x 1998

1998:   /usr/libexec/mysqld --basedir=/usr

Address           Kbytes     RSS   Dirty Mode  Mapping
0000561c0ddea000   60468   13552       0 r-x-- mysqld
0000561c118f7000    1492     672     672 r---- mysqld
0000561c11a6c000    3612     252     224 rw--- mysqld
0000561c11df3000    5300    1524    1524 rw---   [ anon ]
0000561c1403c000   79032   45400   45400 rw---   [ anon ]
00007ff838000000   37204   27912   27912 rw---   [ anon ]
00007ff83a455000   28332       0       0 -----   [ anon ]
00007ff90b6d5000       4       4       4 r---- ld-2.28.so
00007ff90b6d6000       8       8       8 rw--- ld-2.28.so
00007ffcf9398000     132       8       8 rw---   [ stack ]
...
total kB         3439672  655928  638844

Compare "pmap", "ps" and "smem" Reports - Here are the outputs of "pmap", "ps" and "smem" commands on process id 1998 (MySQL Server).

herong$ sudo pmap -x 1998
1998:   /usr/libexec/mysqld --basedir=/usr
...
Address           Kbytes     RSS   Dirty Mode  Mapping
total kB         3439672  655928  638844

herong$ sudo smem -P mysqld
  PID User   Command                Swap     USS     PSS     RSS 
 1998 mysql  /usr/libexec/mysqld  388652  652612  653036  655928 

herong$ ps -o pid,euser,%mem,rss,drs,trs,sz,vsz,comm -p 1998
  PID EUSER    %MEM    RSS     DRS  TRS     SZ     VSZ COMMAND
 1998 mysql     4.1 645924 3439668    0 859917 3439668 mysqld

Those outputs show that:

The VSZ (total memory) usage is 3,439,672 KiB reported by "pmap" and "ps -o vsz" (with a 4 KiB difference).
The RSS (memory mapped in RAM) usage is 655,928 KiB reported by "pmap" and "smem". But "ps -o vsz" reported much lower number, 645 924 KiB. Comparing with VSZ of 3,439,672 KiB, there should be about 2,800,000 KiB memory mapped to the swap space.
However, "smem" only reported a swap usage of 388,652 KiB. So there are about 2,400,000 KiB virtual memory mapped to nowhere. I am not sure why.