Re: anon_vma RFC2

From: William Lee Irwin III
Date: Fri Mar 12 2004 - 19:30:03 EST

On Fri, Mar 12, 2004 at 08:17:49AM -0800, Linus Torvalds wrote:
> I have to _violently_ agree with Andrea on this one.
> The absolute _LAST_ thing we want to have is a "remnant" rmap
> infrastructure that only gets very occasional use. That's a GUARANTEED way
> to get bugs, and really subtle behaviour.
> I think Andrea is 100% right. Either do rmap for everything (like we do
> now, modulo IO/mlock), or do it for _nothing_. No half measures with
> "most of the time".
> Quite frankly, the stuff I've seen suggested sounds absolutely _horrible_.
> Special cases are not just a pain to work with, they definitely will cause
> bugs. It's not a matter of "if", it's a matter of "when".
> So let's make it clear: if we have an object-based reverse mapping, it
> should cover all reasonable cases, and in particular, it should NOT have
> rare fallbacks to code that thus never gets any real testing.
> And if we have per-page rmap like now, it should _always_ be there.
> You do have to realize that maintainability is a HELL of a lot more
> important than scalability of performance can be. Please keep that in
> mind.

The sole point I had to make was against a performance/resource scalabilty
argument; the soft issues weren't part of that, though they may ultimately
be the deciding factor.

-- wli
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