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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 “locked” 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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