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Date:      Wed, 5 Sep 2001 15:11:45 +0200
From:      Tuyet-Tram.Dang-Ngoc@prism.uvsq.fr
To:        freebsd-questions@freebsd.org
Subject:   behaviour of getrusage () on FreeBSD
Message-ID:  <20010905151145.A76514@gibet.prism.uvsq.fr>

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Hello,



	in ordre to know the size of the data allocated in my C
program at certain points of its execution, I wanted to use the 
primitive function 'getrusage ()'

	I encounter some problems when I use getrusage to display
memory usage by a code like the following :

[...]
getrusage (RUSAGE_SELF, &r);

printf ("user time : %ld.%02ld\n", r.ru_utime.tv_sec, \
        r.ru_utime.tv_usec/10000) ;
printf ("system time : %ld.%02ld\n", r.ru_stime.tv_sec, \
        r.ru_stime.tv_usec/10000) ;

ticks = (r.ru_utime.tv_sec + r.ru_stime.tv_sec + \
        r.ru_utime.tv_usec/10000 + r.ru_stime.tv_usec/10000) * clock;
printf ("nombre de ticks : %ld\n", ticks) ;

printf ("max resident set size       : %ld\n", r.ru_maxrss);
printf ("integral shared memory size : %ld\n", r.ru_ixrss / ticks);
printf ("integral unshared data      : %ld\n", r.ru_idrss / ticks);
printf ("integral unshared stack     : %ld\n", r.ru_isrss / ticks);
[...]

	If I make such calls in my main program :

int main ()
{
    /* step 1 */
    Displaying information about getrusage (and be careful about not to
    divide by the number of ticks which is 0 at the beginning)

    /* step 2 */
    big and long processing instructions allocating and using lot of memory

    /* step 3 */
    Displaying information about getrusage.

    [...]
}

	On a FreeBSD 4.3-RELEASE-p14, I get :
* On step 1 :
max resident set size       : 0
integral shared memory size : 0
integral unshared data      : 0
integral unshared stack     : 0
user time           : 0.00
system time               : 0.00
 
   Well, this seems normal, as it has just started.

* On step 3 (after a big instructions), I get :
max resident set size       : 436
integral shared memory size : 4
integral unshared data      : 13
integral unshared stack     : 145
user time           : 0.52
system time               : 8.50

   Well, no comments about these results, it's OK.

	I launch the same program on another computer (a little
more powerful), on  FreeBSD 4.3-RELEASE, and :

* step 1 :
max resident set size       : 0
integral shared memory size : 0
integral unshared data      : 0
integral unshared stack     : 0
user time           : 0.00
system time               : 0.00

* step 3 :
max resident set size       : 0
integral shared memory size : 0
integral unshared data      : 0
integral unshared stack     : 0
user time           : 0.00
system time               : 6.46

	Questions :
	- why the behaviours aren't the same as on the first computer ?
	- why are all the data size, null ?

	And finally with another computer (an old P75) with a 
FreeBSD 5.0-CURRENT, I get :

* step 1 :
max resident set size       : 208
integral shared memory size : 8
integral unshared data      : 8
integral unshared stack     : 256
user time           : 0.00
system time               : 0.00

* step 3 :
max resident set size       : 372
integral shared memory size : 4
integral unshared data      : 12
integral unshared stack     : 130
user time           : 1.88
system time               : 70.39

	- why at step 1 do I have non-null values ?
	- why at step 3, the values are very different from computer 1 and 2 ?

	I also tested on a computer with Linux (but without the division by
tcks as said on its man page), and on step 1 and on step 3, all data size are
always null.


On conclusion, my main questions are :
	- is it a good idea to use getrusage () to get the size of a process 
a *certain* point of its execution (I can't of course watch continuously
a 'top' command or a 'ps -v' command ;-)

	- if yes, how can I use it with a determinist behaviour ?

	- I also saw that if the big processing instructions of 
step 2 are just reduced on the single instruction 'malloc (10000)', 
then the r.ru_*time.tv_*sec are null, and so the values of number of ticks too,
and I will have division by zero, and no hope to get data size.

	- I also look at 'ps' source code and saw that I could use
kvm_getproc (), but it is not portable when I will have to use it for Linux
and other un*x ;

	- someone has told me to make my program read /proc/XXX/map
on FreeBSD and /proc/XXX/status on Linux, but it seems to be a little
"bulky", and I'm not sure I will alway have the rights on this directory.
And it's not portable.

	-another one told me to make fork and generate a core to get the
size, but it's a little "bulky" for me ;-)


	Does someone have an idea please ?



	Thanks in advance,

				Tram

-- 
Tuyêt Trâm ÐANG NGOC <dntt@prism.uvsq.fr>
Laboratoire PRiSM - Université de Versailles
http://www.prism.uvsq.fr/~dntt

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