Subject: Re: pmap_extract()?
To: Eduardo E. Horvath <>
From: Chris G. Demetriou <>
List: tech-kern
Date: 01/16/1997 16:32:29
> I will admit that I had not studied the vm code closely enough to notice
> that the vm code checked to make sure pages were wired before calling
> pmap_extract().  I am still surprized the daemon book makes no mention of
> pmap_extract() as part of the pmap interface.  Was that part of the
> original 4.4BSD implementation, or did it come from somewhere else?

I can't say _for sure_ about 4.4BSD, but uses of pmap_extract() (in
similar places) were definitely in Lite2, and i doubt that code
changed between 4.4 and Lite.

Quite honestly, it doesn't surprise me that the daemon book doesn't
mention it.  It also doesn't include e.g. details on vnode locking
protocols (at least, when i looked for them i couldn't find them!),
which someone studying the 4.4BSD and/or Lite/Lite2 kernels would find

> [ ... ]
> O.K., you can get around this problem by severely restricting the kernel
> address space. [ ... ]

Indeed, why would you _not_ do this?  Why does the _kernel_ need a
64-bit, or even 43- or 40-bit virtual address range?