thrash(1)

NAME
     thrash - thrash memory to explore paging behavior

SYNOPSIS
     thrash [args]

DESCRIPTION
     thrash will allocate a region of its virtual memory of a size given by
     its arguments, and either randomly or sequentially access that memory in
     order to explore the system paging behavior.

     The amount of memory to thrash over is specified by a size flag followed
     by an integer argument, whose units are determined by the particular size
     flag used.  The flag may be -m, for megabytes, -p, for pages; or -k for
     kilobytes.  An additional argument of -s implies sequential thrashing;
     the default is random.  Another optional argument, -n count, gives the
     number of references to make before exiting; it defaults to 10000.  An
     optional argument -w followed by an integer time tells thrash to sleep
     for ``time'' seconds after thrashing, but before exiting.

     Once the memory is allocated, thrash prints a message on stdout saying
     how much it is using, and then proceeds to thrash over it.

USAGE
     thrash can be used, in conjunction with cvusage and squeeze to determine
     the approximate available working memory on a system.  To do so, run the
     command:
                    ssusage thrash -m 4
     which asks thrash to use about 4 MB of memory.  When the command
     completes, the resource usage of thrash is printed; the value labeled
     majf gives the number of major page faults it took, that is the number of
     faults that required a physical read.  When run on a machine with a large
     amount of physical memory, this value is the number of faults needed to
     start the program, which is the minimum number for any run.

     Then, as superuser, and in a separate window, run squeeze to lock down
     varying amounts of memory, and rerun ``ssusage thrash -m 4".  The major-
     fault number will remain low at first, but as you squeeze out more and
     more memory, it will rise.  The amount of available memory reported by
     squeeze at point at which thrash begins to page-fault tells you the
     combined working set of thrash (~ 4MB), the kernel, and any other
     applications you have running.

SEE ALSO
     ssusage(1), squeeze(1)