Re: page table lock patch V15 [0/7]: overview

[Hugh Dickins]

On Wed, 12 Jan 2005, Andrew Morton wrote:
> Nick Piggin <nickpiggin@xxxxxxxxxxxx> wrote:
> >
> > Christoph Lameter wrote:
> >  > Changes from V14->V15 of this patch:
> > 
> >  I wonder what everyone thinks about moving forward with these patches?
> 
> I was waiting for them to settle down before paying more attention.

They seem to have settled down, without advancing to anything satisfactory.
7/7 is particularly amusing at the moment (added complexity with no payoff).

> My general take is that these patches address a single workload on
> exceedingly rare and expensive machines.

Well put.  Christoph's patches stubbornly remain a _good_ hack for one
very specific initial workload (multi-parallel faulting of anon memory)
on one architecture (ia64, perhaps a few more) important to SGI.
I don't see why the mainline kernel should want them.

> If they adversely affect common
> and cheap machines via code complexity, memory footprint or via runtime
> impact then it would be pretty hard to justify their inclusion.

Aside from 7/7 (and some good asm primitives within headers),
the code itself is not complex; but it is more complex to think about,
and so less obviously correct.

> Do we have measurements of the negative and/or positive impact on smaller
> machines?

I don't think so.  But my main worry remains the detriment to other
architectures, which still remains unaddressed.

Nick's patches (I've not seen for some while) are a different case:
on the minus side, considerably more complex; on the plus side,
more general and more aware of the range of architectures.

I'll write at greater length to support these accusations later on.

Hugh

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