Without wishing to weigh in on whether this caching is a good idea... Wouldn't it be simpler, rather than having two separate "alloc" and "flush" caches, to have a single larger cache, such that whenever it becomes full we bulk flush the top half, and when it's empty we bulk alloc the bottom half? That should mean fewer branches, fewer instructions etc. than having to decide which cache to act upon every time.
-ed
