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<h5 class="subsubsection">3.2.2.6 Efficiency Considerations for <code>malloc</code></h5>

<p><a name="index-efficiency-and-_0040code_007bmalloc_007d-270"></a>

   <p>As opposed to other versions, the <code>malloc</code> in the GNU C Library
does not round up block sizes to powers of two, neither for large nor
for small sizes.  Neighboring chunks can be coalesced on a <code>free</code>
no matter what their size is.  This makes the implementation suitable
for all kinds of allocation patterns without generally incurring high
memory waste through fragmentation.

   <p>Very large blocks (much larger than a page) are allocated with
<code>mmap</code> (anonymous or via <code>/dev/zero</code>) by this implementation. 
This has the great advantage that these chunks are returned to the
system immediately when they are freed.  Therefore, it cannot happen
that a large chunk becomes &ldquo;locked&rdquo; in between smaller ones and even
after calling <code>free</code> wastes memory.  The size threshold for
<code>mmap</code> to be used can be adjusted with <code>mallopt</code>.  The use of
<code>mmap</code> can also be disabled completely.

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