02-17-2015
PS: Used/Free memory in a VM system is pretty meaningless. Once a system goes quiescent, the free memory just represents recent proceess terminations, which make a bunch of free pages. Pages may be used for old mmap(), perhaps by ld() the dynamic linker, and remain mapped in speculation of future use. If there is demand for free memory, and they are not modified, then they can be repurposed immediately, but the memory is in use, used. Whe a process exits, the RAM used for stack and heap are returned to the free memory pool, awaiting use by the nest consumer.
It is more useful to look at page writes and reads of swap per second, to determine if there is a RAM shortage. There are also many ways to tune a system for lower swap I/O, but that is very much an art, sometimes a proprietary product. If you are writing the apps, then there are also many ways to control RAM demand. Paging, in and of itself, may be the right behavior for what is going on, such as extensive interrogation of a huge database. I often see high page faults on virus scanners, as their dictionary is huge.
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LEARN ABOUT ULTRIX
vmstat
vmstat(1) General Commands Manual vmstat(1)
Name
vmstat - report virtual memory statistics
Syntax
vmstat [ interval [ count ] ]
vmstat -v [ interval [ count ] ]
vmstat -fKSsz
vmstat -Kks namelist [ corefile ]
Description
The command reports statistics on processes, virtual memory, disk, trap, and cpu activity.
If is specified without arguments, this command summarizes the virtual memory activity since the system was last booted. If the interval
argument is specified, then successive lines are summaries of activity over the last interval seconds. Because many statistics are sampled
in the system every five seconds, five is a good specification for interval; other statistics vary every second. If the count argument is
provided, the statistics are repeated count times.
When you run the format fields are as follows:
Procs: information about numbers of processes in various states.
r in run queue
b blocked for resources (i/o, paging, and so on.)
w runnable or short sleeper (< 20 seconds) but swapped
faults: trap/interrupt rate averages per second over the last 5 seconds.
in (non clock) device interrupts per second
sy system calls per second
cs cpu context switch rate (switches/second)
cpu: breakdown of percentage usage of cpu time
us user time for normal and low priority processes
sy system time
id cpu idle time
Memory: information about the use of virtual and real memory. Virtual pages are considered active if they belong to processes which are
running or have run in the last 20 seconds.
avm active virtual pages
fre size of the free list
Pages are reported in units of 1024 bytes.
If the number of pages exceeds 9999, it is shown in a scaled representation. The suffix k indicates multiplication by 1000 and the suffix
m indicates multiplication by 1000000. For example, the value 12345 appears as 12k.
page: information about page faults and paging activity. These are averaged every five seconds, and given in units per second. The size
of a unit is always 1024 bytes and is independent of the actual page size on a machine.
re page reclaims (simulating reference bits)
at pages attached (found in free list not swapdev or filesystem)
pi pages paged in
po pages paged out
fr pages freed per second
de anticipated short term memory shortfall
sr pages scanned by clock algorithm, per-second
disk: s0, s1 ...sn: Paging/swapping disk sector transfers per second (this field is system dependent). Typically paging is split across
several of the available drives. This will print for each paging/swapping device configured into the kernel.
Options
-f Provides reports on the number of forks and vforks since system startup and the number of pages of virtual memory involved in each
kind of fork.
-K Displays usage statistics of the kernel memory allocator.
-k Allows a dump to be interrogated to print the contents of the sum structure when specified with a namelist and corefile. This is
the default.
-S Replaces the page reclaim (re) and pages attached (at) fields with processes swapped in (si) and processes swapped out (so).
-s Prints the contents of the sum structure, giving the total number of several kinds of paging related events that have occurred since
boot.
-v Prints an expanded form of the virtual memory statistics.
-z Zeroes out the sum structure if the UID indicates root privilege.
Examples
The following command prints what the system is doing every five seconds:
vmstat 5
To find the status after a core dump use the following:
cd /usr/adm/crash
vmstat -k vmunix.? vmcore.?
Files
Kernel memory
System namelist
vmstat(1)