01-19-2019
Note that some systems actively try to use otherwise unused memory to speed up running processes. For example, if a process starts reading from a large file, the system might read the next few blocks (or megabytes) of that file into a system buffer so the data will be in memory without having to wait for the disk to rotate if that process reads the next block.
If other processes start up need the memory that was used for read-ahead buffers they can be reallocated to the next process without affecting how fast the new process can be loaded.
Different versions of BSD, Linux, and UNIX systems use different algorithms to try to make efficient use of memory. And, different releases of each of those systems may change the algorithms as the vendors think they have learned something from past experiences.
In other words, there can be lots of "free" memory may be used to hold data that may soon be useful to someone even though it can be re-allocated immediately if someone asks for it to be put to a specific use.
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memx(8) System Manager's Manual memx(8)
NAME
memx - memory exerciser
SYNOPSIS
/usr/field/memx -s [-h] [-ofile] [-ti] [-mj] [-pk]
OPTIONS
The memx options are as follows: Print the help message for the memx command. Disables automatic shared memory testing. Save diagnostic
output in file. Run time in minutes (i). The default is to run until the process receives a CTRL-C or a kill -15 pid command. The memory
size in bytes (j) to be tested by each spawned process. Must be greater than 4095. The default is (total-memory)/20. The number of pro-
cesses to spawn (k). The default is 20. The maximum is also 20.
DESCRIPTION
The memx memory exerciser spawns processes to exercise memory by writing and reading three patterns: 1's and 0's, 0's and 1's, and a random
pattern.
You specify the number of processes to spawn and the size of memory to be tested by each process. If the shmx Shared Memory exerciser is
present, it will be the first process spawned; the remaining processes are standard memory exercisers. The memx exerciser will run until
the process receives a CTRL-C or a kill -15 pid command.
A logfile for you to examine and then remove is created in the current working directory. If there are errors in the logfile, check the
syslog file where the driver and kernel error messages are saved.
RESTRICTIONS
The memx exerciser is restricted by the size of the available swap space. The size of the swap space and the size of internal memory
available determines how many processes can run on the system. For example, If there is 16 Mbytes of swap space and 16 Mbytes of memory,
all of the swap space would be used if all 20 spawned memory exercisers are running. In that event, no new processes would be able to run.
On systems with large amounts of memory and small swap space, you must restrict the number of memory exercisers and/or the size of memory
being tested.
If there is a need to run a system exerciser over an NFS link or on a diskless system there are some restrictions. For exercisers that
need to write into a file system, such as fsx(8), the target file system must be writable by root. Also, the directory in which any of the
exercisers are executed must be writable by root because temporary files are written into the current directory. These latter restrictions
are sometimes difficult to overcome because often NFS file systems are mounted in a way that prevents root from writing into them. Some of
the restrictions may be overcome by copying the exerciser to another directory and then executing it.
You should specify the -s option to disable automatic shared memory testing, which is not supported.
EXAMPLES
The following example tests all of memory by running 20 spawned processes until a CTRL-C or kill -15 pid command is received: %
/usr/field/memx The following example runs 10 spawned processes, memory size 500,000 bytes, for 180 minutes in the background. %
/usr/field/memx -t180 -m500000 -p10 &
SEE ALSO
Commands: cmx(8), diskx(8), fsx(8), shmx(8), tapex(8)
memx(8)