Question

If you are developing a memory intensive application in C++ on Windows, do you opt to write your own custom memory manager to allocate memory from virtual address space or do you allow CRT to take control and do the memory management for you ? I am especially concerned about the fragmentation caused by the allocation and deallocation of small objects on heap. Because of this, I think the process will run out of memory eventhough there is enough memory but is fragmented.

Answer 1

I think your best bet is to not implement one until profiles prove that the CRT is fragmenting memory in a way that damages the performance of your application. CRT, core OS, and STL guys spend a lot of time thinking about memory management.

There’s a good chance that your code will perform quite fine under existing allocators with no changes needed. There’s certainly a better chance of that, than there is of you getting a memory allocator right the first time. I’ve written memory allocators before for similar circumstances and it’s a monsterous task to take on. Not so suprisingly, the version I inherited was rife with fragmentation problems.

The other advantage of waiting until a profile shows it’s a problem is that you will also know if you’ve actually fixed anything. That’s the most important part of a performance fix.

As long as you’re using standard collection classes an algorihtmns (such as STL/BOOST) it shouldn’t be very hard to plug in a new allocator later on in the cycle to fix the portions of your code base that do need to be fixed. It’s very unlikely that you will need a hand coded allocator for your entire program.