Re: [PATCH 2/2] page table iterators

[Nick Piggin <nickpiggin@yahoo.com.au>]

Andi Kleen wrote:
> On Thu, Feb 17, 2005 at 03:30:31PM -0800, David S. Miller wrote:
> 
>>On Fri, 18 Feb 2005 00:03:42 +0100
>>Andi Kleen <ak@suse.de> wrote:
>>
>>
>>>And to be honest we only have about 6 or 7 of these walkers
>>>in the whole kernel. And 90% of them are in memory.c
>>>While doing 4level I think I changed all of them around several
>>>times and it wasn't that big an issue.  So it's not that we
>>>have a big pressing problem here... 
>>
>>It's super error prone.  A regression added by your edit of these
> 
> 
> Actually it was in Nick's code (PUD layer ;-).  But I won't argue
> that my code didn't have bugs too...
> 
> 

I won't look back to see where the error came from :) But
yeah it is equally (if not more) likely to have come from
me. And it probably did happen because all the code is
slightly different and hard to understand.

>>walkers for the 4level changes was only discovered and fixed
>>yesterday by the ppc folks.
>>
>>I absolutely support any change which consolidates these things.
> 
> 
> The problem is just that these walker macros when they
> do all the lazy walking stuff will be quite complicated.
> And I don't really want another uaccess.h-like macro mess.
> 
> Yes currently they look simple, but that will change.
> 

But even in that case, it will still be better to have the
extra complexity once in the macro rather than throughout mm/

> Open coding is probably the smaller evil.
> 
> And they're really not changed that often.
> 

It is not so much a matter of changing, so much as having 10
slightly different implementations.

I think it should be easier to go from the iterators patch to
perhaps more complex iterators, or some open coding, etc etc.
rather than try to put a big complex pt walker on top of these
10 different open coded implementations.

But perhaps I'm missing something you're not - I'd need to see
the lazy walking code I guess.

Nick