THRASH(1)							     THRASH(1)

NAME    [Toc]    [Back]

     thrash - thrash memory to explore paging behavior

SYNOPSIS    [Toc]    [Back]

     thrash [args]

DESCRIPTION    [Toc]    [Back]

     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    [Toc]    [Back]

     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 majorfault
 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    [Toc]    [Back]

     ssusage(1), squeeze(1)


									PPPPaaaaggggeeee 1111