> And at least we aren't trashing the cache hierarchy up front – if we delay the zero'ing until we were going to write to the pages anyway, then that means both

> And at least we aren't trashing the cache hierarchy up front – if we delay the zero'ing until we were going to write to the pages anyway, then that means both writes happen at the same time, so we only have to pay one set of TLB / L2 cache / etc. misses. Ooh, nice one. My first impression was that calloc was just lazy-allocating, which is fine in most cases but when you want precise control over timing, maybe you want to be sure that memory is zero'd at allocating time rather than pay the cost unexpectedly at use time. But the cache-awareness makes that a moot point. You'd be paying double cache-eviction costs if you were clearing that memory up front: once at clearing time, and once at actual-writing time. This implementation of calloc avoids that.