Re: [RFC][PATCH 0/10] alternate 4-level page tables patches

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

Andi Kleen wrote:
> On Wed, Dec 22, 2004 at 10:19:09PM +1100, Nick Piggin wrote:
> 
>>But the advantages I see in the source code are a) pud folding matches 
>>exactly
>>how pmd folding was done on 2 level architectures, and b) it doesn't touch
>>either of the "business ends" of the page table structure (ie. top most or
>>bottom most levels).  I think these two points give some (if only slight)
>>advantage in maintainability and consistency.
> 
> 
> Sure, but when it's merged then pml4_t (or p<whatever>_t) would be 
> the "business end", so it doesn't make much difference longer term.
> After all future linux coders will not really care what was in the
> past, just what is in the code at the time they hack on it.
> 

Yeah OK, raw-code wise the pml4 patch isn't much different. But the
conceptual intrusiveness of having the folding 'magic' in the top
level page table is a bit higher.

Also, pml4 does have some implementation intrusiveness by introducing
a new _way_ of folding the table, whereas pud folds in the same manner
as pmd.

> 
> 
>>If I can get the bulk of the architectures changed and tested, the arch
>>maintainers don't kick up too much fuss, it has a relatively trouble free 
>>run
>>in -mm, and Andrew and Linus are still happy to merge before 2.6.11, would 
>>you
>>be OK with the pud version (in principle)?
> 
> 
> I can't say I'm very enthusiastic about it (but more due to scheduling
> issues than technical issues). I don't see anything wrong with them by itself,
> but I also don't think they have any particular advantages over the
> pml4 version. But in the end the main thing I care about is that
> 4 level pagetables get in in some form, where exactly the
> new level is added and how it is named is secondary.
> 

So long as you are not completely against it, that is a good start ;)

> I would prefer if it happened sooner though because the work
> is not finished (the optimized walking is still needed),
> and i've been just waiting for getting merged and settled
> down a bit before continuing. 
> 

Yeah sure. I can also try to help with that (regardless of which patch
is merged).
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