Memory Usage

Linux Commands to Monitor Memory Usage

vmstat	Monitor virtual memory
free	Display amount of free and used memory in the system. (Also: cat /proc/meminfo)
pmap	Display/examine memory map and libraries (so). Usage: pmap pid
top	Show top processes
sar -B	Show statistics on page swapping.
time -v date	Show system page size, page faults, etc of a process during execution. Note you must fully qualify the command as "/usr/bin/time" to avoid using the bash shell command "time".
cat /proc/sys/vm/freepages	Display virtual memory "free pages". One may increase/decrease this limit: echo 300 400 500 > /proc/sys/vm/freepages
cat /proc/meminfo	Show memory size and usage.

Examination of memory usage:

Show system page size: /usr/bin/time -v date

        ...
        Page size (bytes): 4096
        Exit status: 0

Show paging: /usr/bin/time -v firefox

        ...
        Major (requiring I/O) page faults: 24
        Minor (reclaiming a frame) page faults: 11271
        Voluntary context switches: 302
        Involuntary context switches: 3689
        ...

Explanation of terms:

Major Page Fault (MPF): When a request for memory is made but it does not exist in physical memory, a request to the disk subsystem to retrieve pages from virtual memory and buffer them in RAM. The MPF occurs most when an application is started.
Minor Page Fault (MnPF): Reusing a page in memory as opposed to placing it back on disk