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Date: Sun, 10 Apr 2011 11:34:24 -0400
From: Rich Felker <>
Subject: Re: Simple testing task - string functions

On Sun, Apr 10, 2011 at 10:25:59PM +0700, JIghtuse wrote:
> I have some questions about my task. I've written a program to test
> malloc() function of musl. But..
> 1. Can I use standart rand() and srand() functions to generate
> random size of allocated memory chunks, or I must to write another
> one random number generator?

I don't mind if you use them as long as you make the default behavior
deterministic, i.e. don't seed it with time or something where we
might get a failure and then not be able to reproduce it. Or you could
use time as a seed by default if you print it so it's not lost on
failure. This is all stuff that could be changed later anyway. I just
don't want to have a situation where we saw one failure but can't
reproduce it without trying all 2billion possible seeds. :)

> Write a program which loops many times allocating and freeing memory
> So, when my program must to free memory? If it freeing just after
> its allocating, it always gets one chunk of memory. And how to

If you just allocate chunk X and then free chunk X, it won't affect
fragmentation at all. You'll need to do some shuffling. There's some
code in libc-bench (see musl gitweb server) which attempts to do the
sort of random allocation patterns I have in mind, but I haven't
evaluated how good a job it actually does at fragmenting memory. You
could use it as an idea or starting point.

Or if you want to do it from scratch, read up on how hard disks get
fragmented and apply the same principles to memory.

If you're stuck, I also just thought of a simple algorithmic way to
generate fragmentation which I could explain.

> 3. I decided to generate a fragmentation diagram as a .dat file for
> plotting by gnuplot. Are you satisfied with it, or maybe write it as
> a simple text file with pseudo-graphic diagram?

Either or both would be fine.


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