[KMag]

> I don't understand why it is slower. It has to be zeroed anyway.

Memory pages freed from userspace might be reused in kernelspace.

If, for instance, the memory is re-used in the kernel's page cache, then the kernel doesn't need to zero it out before copying the to-be-cached data into the page.

Edit: I seem to remember back in the 1990s that the kernel at least in some cases wouldn't zero-out pages previously used by the kernel before giving them to userspace, sometimes resulting in kernel secrets being leaked to arbitrary userspace processes. Maybe I'm missremembering, and it was just leakage of secrets between userspace processes. In any case, in the 1990s, Linux was way too lax about leaking data from freed pages.