Re: [PATCH]Fix broken VMI in 2.6.27-rc..

[Jeremy Fitzhardinge]

H. Peter Anvin wrote:
> Jeremy Fitzhardinge wrote:
> > > The Linux kernel was never a paragon of perfection - it was never 
> > > meant to be.  Just because a bit of cruft went unnoticed into the 
> > > kernel doesn't mean we shouldn't fix it.
> >
> > I don't really see what the issue is.
> >
> > Fixmaps are primarily used for things that need to be mapped early 
> > before we can allocate address space dynamically.  They're 
> > predominantly used for boot-time init, and rarely on any 
> > performance-critical path.  The only vaguely regular use a fixmap 
> > gets during runtime is poking at apics, and that's dominated by IO 
> > time, and kmap_atomic.  Statically, there's only 100 references in 
> > the kernel.  And it only affects 32-bit.
> >
> > Having fixmaps at link-time fixed addresses would be nice, I suppose, 
> > but hardly worth going to vast effort over.
>
> No, but it's hardly vast effort, either.

Thinking about it, the fixmap really has to be as high as possible.  If 
it were any lower, then it would either truncate the 1:1 mapping, or 
shadow some physical memory.

   J
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