I've been looking through some of the jemalloc code and had a question about bitmap.h. Testing on a 64-bit machine, the arena bin with the most elements is size=8 with 501 items. Since a cacheline is commonly 64 bytes = 512 bits, a simpler single-level bitmap would seem to win just on memory effects. It's not clear to me if its advantageous on a branching basis, at least on 64-bit. On average you'd need to look at 4 words to find an unused 8-byte entry, and fewer for other size bins. I guess on a 32-bit platform, it might be a different story. Still, I wonder if it is worth touching another cache line to avoid the comparisons. Are there cases where the bitmap code is used for more than 512 items in it? -Mitch