Re: Linux-2.5.17

[Linus Torvalds]

On Wed, 22 May 2002, Roman Zippel wrote:
>
> We already don't let the general vm touch the pgd entries for the same
> reason, so I don't think that's really a big problem.
> Using the present bit has another consequence. unmap() had to be done in
> two phases:

I don't disagree. Are you interested in trying to write it up? It sounds
like a potentially good idea, with few downsides (but I can imagine some:
it does bad things to threads that just happen to share the same 4M area
for other stuff, and that start getting spurious page faults on another
CPU because _their_ area temporarily went away from under them).

I also suspect that it might simplify the TLB shootdown enough that we
wouldn't _have_ to split out the exit case and could use the shared
zapping. But I'm kind of worried about the potential threading issues.

(Rule of thumb: it's always a bad idea to cut down on parallelism, and
we'll _really_ be up shit creek if some threaded app comes along later
where munmap() ends up serializing threads too much).

			Linus