&gt; Ehh, that doesn&#x27;t apply to what he&#x27;s talking about though.<p>Of course it does.<p>&gt;  That only works when the pages are actually freed. Since actually asking the kernel for more memory is expensive, most malloc&#x2F;calloc implementations will hold-on to some pages since it assumes you&#x27;re going to allocate more. Since it reuses this memory without ever giving it back to the kernel, the kernel won&#x27;t zero it for us.<p>It&#x27;s what the standard system malloc does, possibly in cooperation with the kernel but not necessarily so (why would it need the kernel involved after all?)<p>Just as OpenBSD&#x27;s malloc framework can do way more than trivially request memory from the kernel: <a href="http:&#x2F;&#x2F;www.openbsd.org&#x2F;cgi-bin&#x2F;man.cgi&#x2F;OpenBSD-current&#x2F;man5&#x2F;malloc.conf.5?query=malloc%2econf" rel="nofollow">http:&#x2F;&#x2F;www.openbsd.org&#x2F;cgi-bin&#x2F;man.cgi&#x2F;OpenBSD-current&#x2F;man5&#x2F;...</a>. In fact, since OpenBSD 5.6 it&#x27;ll junk small allocations on freeing (fill them with 0xdf) by default. And as usual that uncovered broken code…<p>&gt; When we started junking memory by default after free, the postgres ruby gem stopped working.