Re: mmotm 2009-02-02-17-12 uploaded (x86/nopmd etc.)

Andrew Morton
2009-02-04T21:26:13Z

On Wed, 4 Feb 2009 21:08:46 +0100
Ingo Molnar <mingo@elte.hu> wrote:

>
> * Andrew Morton <akpm@linux-foundation.org> wrote:
>
> > > > This is getting painful.
> > >
> > > the include file spaghetti is ... interesting there, and it's historic.
> > >
> > > I could blame it on highmem, PAE or paravirt - but i'll only blame it on
> > > paravirt for now because those developers are still around! ;-)
> > >
> > > Jeremy, any ideas how to reduce the historic dependency mess in that area?
> > > I think we should go on three routes at once:
> > >
> > > - agressive splitup and separation of type definitions from method
> > > declaration (+ inline definitions). The spinlock_types.h / spinlock.h
> > > splitup was really nice in solving such dependency problems.
> >
> > I like this one. The mixing up of declare-something with use-something
> > is often the source of our woes.
>
> yes. I mapped this problem area once and this is how the include file
> spaghetti gets generated in practice:
>
> - type A gets declared
> - type A gets _used_ in the same file in an inline method, BUT,
>
> that usage also brings in instantiated use of type X1, X2 and X3.
>
> if all types are declared like that everywhere, it can be seen (and it's a
> mathematical certainty) that the only conflict-free way of doing this is to:
>
> - initially add random #include lines to bring in type X1, X2 and X3.
> Which brings in recursive dependencies from those X1 X2 and X3 files.
>
> - when the stuff hits the fan then folks are in a big mess already and
> only a deep restructuring could gets them out of it - which they rarely
> do in an iterative environment. So they work it around iteratively:
> instead of new nice inline methods [which we really prefer] they delay
> all the 'usage' instantiation to .c file via the use of CPP macros
> [which we hate because they hide bugs and cause bugs].

None of which would happen if we didn't also have an inlining fetish.