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From: Nick Barnes <Nick.Barnes@pobox.com>
To: Nik Clayton <nik@freebsd.org>
In-Reply-To: <44077091.3060604@freebsd.org> 
	from Nik Clayton <nik@freebsd.org> 
	of "Thu, 02 Mar 2006 22:24:17 +0000"
Date: Thu, 02 Mar 2006 23:50:29 +0000
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Sender: nb@ravenbrook.com
Cc: stable@freebsd.org
Subject: Re: Failing to understand getrusage() 
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At 2006-03-02 22:24:17+0000, Nik Clayton writes:
> I'm failing to understand how getrusage() works, which is a bit perplexing,
> because it doesn't seem like it would be terribly complicated.

ru_maxrss is the maximum resident set size, not the heap size.
malloc(big) doesn't grow the resident set.  Touching the memory you
have allocated will grow the resident set.  Try this:

        getrusage(RUSAGE_SELF, &ru);
        printf("%lu\n", ru.ru_maxrss);
        p = malloc(SIZE);
        assert(p)
        getrusage(RUSAGE_SELF, &ru);
        printf("%lu\n", ru.ru_maxrss);
        for (i=0; i<SIZE; ++i) {
                p[i] = 0;
        }
        getrusage(RUSAGE_SELF, &ru);
        printf("%lu\n", ru.ru_maxrss);

Nick B