I usually use doubling, but I just recently landed a patch to expand by a factor of 8 instead, which sped up a microbenchmark (of constructing a JSON string, fw

I usually use doubling, but I just recently landed a patch to expand by a factor of 8 instead, which sped up a microbenchmark (of constructing a JSON string, fwiw) by 50%. Someone saw in a profile that we were spending a lot of time in realloc in a task that involved building a string in contiguous memory. But the final string was realloc'd down to its actual size, so it was safe to get a lot more aggressive with the growth to avoid copying. The overhead was only temporary. It turns out that powers of 8 get big fast, so there are now many fewer copies and the few that happen are copying a small portion of the overall data, before a final octupling that provided mostly unused space that didn't cost much. Know your problem, I guess?