Malloc vs custom allocator: Malloc has a lot of overhead. Why?

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On Windows 7 you will always get the low-fragmentation heap allocator, without explicitly calling HeapSetInformation() to ask for it. That allocator sacrifices virtual memory space to reduce fragmentation. Your program is not actually using 170 megabytes, you are just seeing a bunch of free blocks lying around, waiting for an allocation of a similar size.

This algorithm is very easy to beat with a custom allocator that doesn’t do anything to reduce fragmentation. Which may well work out for you, albeit that you don’t see the side effects of it until you keep the program running longer than a single debug session. You do need to make sure it is stable for days or weeks if that is the expected usage pattern.

Best thing to do is just not fret about it, 170 MB is rather small potatoes. And do keep in mind that this is virtual memory, it doesn’t cost anything.

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