Yeah, this. Unless you are zeroing a really big chunk of memory, you expect that it might already be in the cache and you almost always want it in the cache af

Yeah, this. Unless you are zeroing a really big chunk of memory, you expect that it might already be in the cache and you almost always want it in the cache after, so pushing it down to the memory is often counter-productive in this sense: you want it close to the core. Zeroing memory does take up a non-negligible amount of time some some workflows, especially those that make sparse use of the memory (e.g., don't end up writing all the memory in the end, think a large-radix histogram where many counters stay zero, or allocations that are larger than needed and don't end up getting used, etc). That said, zeroing can be pretty fast as this post shows: around 30 bytes per cycle, which on a 4 GHz CPU is 120 GB/s. AVX-512 doubles that to ~60 bytes/cycle.