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    <p>No, the virtual address space of a process is not necessarily contiguous. In the old days, a process obtained memory through <a href="http://www.kernel.org/doc/man-pages/online/pages/man2/brk.2.html" rel="nofollow noreferrer"><code>brk</code></a>, which indeed forced the process heap to be a contiguous zone of memory. Nowadays memory allocation is done through <a href="http://www.kernel.org/doc/man-pages/online/pages/man2/mmap.2.html" rel="nofollow noreferrer"><code>mmap</code></a>, which can manipulate the process's virtual memory page by page.</p> <p>If you're curious about the kernel side of things, I recommend two references:</p> <ul> <li>Read a book on the Linux kernel, such as <a href="http://lwn.net/Kernel/LDD3/" rel="nofollow noreferrer"><em>Linux Device Drivers</em> by Jonathan Corbet, Alessandro Rubini, and Greg Kroah-Hartman</a>, in particular <a href="http://lwn.net/images/pdf/LDD3/ch08.pdf" rel="nofollow noreferrer">chapter 8 (Allocating Memory)</a>.</li> <li>Browse the kernel code through <a href="http://lxr.linux.no/linux" rel="nofollow noreferrer">LXR, the Linux kernel cross-reference</a>. The memory management code is in the <a href="http://lxr.linux.no/#linux+v2.6.38/mm" rel="nofollow noreferrer"><code>mm</code> directory</a>; start with <a href="http://lxr.linux.no/#linux+v2.6.38/mm/mmap.c" rel="nofollow noreferrer"><code>mmap.c</code></a> or <a href="http://lxr.linux.no/#linux+v2.6.38/include/linux/mm.h" rel="nofollow noreferrer"><code>mm.h</code></a>.</li> </ul> <p>If you'd like to explore around on your system, you can see each process's memory mapping in <code>/proc/$pid/maps</code>. See <a href="https://unix.stackexchange.com/questions/6301/how-do-i-read-from-proc-pid-mem-under-linux">How do I read from /proc/$pid/mem under Linux?</a> for more information.</p>
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    1. COI think dlmalloc derivatives still use `brk()` for allocations under a certain threshold, though I'll admit I haven't looked at this recently. OTOH, IIRC, OpenBSD uses `mmap()` for every allocation.
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