using malloc on custom memory allocator about memory-allocators HOT 1 CLOSED

Hey,

Thank you for the kind words. I did this project a while ago and I can't believe people still find it useful.

You're right about everything you said. The arena or other custom allocators work by doing fewer malloc calls (usually on startup) and then managing the memory by themselves, instead of doing a malloc every time. It is effectively one memory tool on top of another.

Why we need an additional memory tool on top of malloc? Malloc performance is not terrible but it's a bit inconsistent and sometimes it can be really slow. Malloc usually takes the memory from the user/app space if there's some available but if there's not, it needs to do system/OS call to request for more memory. This operation requires to switch the context (from user to OS and the back again to user). This is absurdly slow. The point of doing fewer mallocs, specially at start up is to reduce these slow operations, we'll do them once and that's it. After that, our allocations will be super fast.

Why the OS doesn't do that for us? Well, because it doesn't know how much memory our program will use but we do, or at least we have a rough idea. Having this information, allows us to allocate the memory in advance for our custom allocator and save syscalls.

I am no expert in this matter, so I suggest you to research about this interesting topic,

All the best,
Mariano.

from memory-allocators.