Question

Is there anything wrong with the optimization of overloading the global operator new to round up all allocations to the next power of two? Theoretically, this would lower fragmentation at the cost of higher worst-case memory consumption, but does the OS already have redundant behavior with this technique, or does it do its best to conserve memory?

Basically, given that memory usage isn’t as much of an issue as performance, should I do this?

Answer 1

The default memory allocator is probably quite smart and will deal well with large numbers of small to medium sized objects, as this is the most common case. For all allocators, the number of bytes requested is never always the amount allocated. For example, if you say:

char * p = new char[3];

the allocator almost certainly does something like:

char * p = new char[16];   // or some minimum power of 2 block size

Unless you can demonstrate that you have an actual problem with allocations, you should not consider writing your own version of new.