&gt; Would you mind providing some more information on this? I googled it but I couldn&#x27;t find any documentation on what you describing.<p>I was talking about <a href="https:&#x2F;&#x2F;www.freebsd.org&#x2F;doc&#x2F;en&#x2F;articles&#x2F;vm-design&#x2F;prefault-optimizations.html" rel="nofollow">https:&#x2F;&#x2F;www.freebsd.org&#x2F;doc&#x2F;en&#x2F;articles&#x2F;vm-design&#x2F;prefault-o...</a> but after actually re-checking the docs rather than going from bitrotted memory pre-zeroing only happens for the initial zero-fill fault, so the original calloc is &quot;free&quot; (if there are zeroed pages in the queue) but freeing then re-calloc&#x27;ing will need to zero the chunk (unless the allocator decides to go see if the kernel has pre-zeroed space instead I guess). My bad.<p>&gt; To be clear though, the parent commenter (and I) are talking about the pages that malloc keeps around in the processes memory to be reused (And thus are never released back to the OS).<p>Yeah so was I, but I was misremembering stuff.<p>&gt; Are you saying FreeBSD&#x2F;OpenBSD&#x2F;others have a system to tell the kernel when a user process has pages it plans to zero, and then a system for the kernel to notify the process when&#x2F;if it does?<p>Turns out no.