Date: Tue, 7 Mar 2006 02:15:56 +0300 From: Yar Tikhiy <yar@comp.chem.msu.su> To: Nick Barnes <Nick.Barnes@pobox.com> Cc: stable@freebsd.org Subject: Re: Failing to understand getrusage() Message-ID: <20060306231556.GB64952@comp.chem.msu.su> In-Reply-To: <80813.1141343429@thrush.ravenbrook.com> References: <44077091.3060604@freebsd.org> <80813.1141343429@thrush.ravenbrook.com>
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On Thu, Mar 02, 2006 at 11:50:29PM +0000, Nick Barnes wrote:
> 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);
Well, there was a call to memset() in the original Nik's program
while your code just does the same by itself.
Personally, I'd like to say a "me too". /me too fails to see why
in a quiet, idle system ru_maxrss is very unpredictable over numerous
runs of the test program, both before and after the malloc+memset.
Filling the memory with a non-zero value doesn't matter. Is it the
Heizenberg daemon at work? :-)
--
Yar
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