I forgot that this GC is non-moving (I'm not used to that assumption, and it was a bit of a quick comment).

I do find the statement dubious still, do you mind clearing it up for me?

Given a page { void* addr; size_t size; size_t alignment; BitMap used; } where used's size in bits is page.size / page.alignment, surely we only need to visit the used bitmap for marking a memory slot as free?

Yes, I agree. (This thread continued in https://news.ycombinator.com/item?id=45137286.)

You’re correct, I forgot about that optimisation!