Re: Page aging broken in 2.6

[Linus Torvalds]

On Sat, 27 Dec 2003, Benjamin Herrenschmidt wrote:
> 
> Or do what I propose here, that is have ptep_test_and_clear_* be
> responsible for the flush on archs where it is necessary, but then
> it would be nice to have more than the ptep as an argument...

The dirty handling already does the TLB flush (in that case it's a 
correctness issue, not a hint). So it's only ptep_test_and_clear_young() 
that matters.

I don't know whather that ever ends up being performance-critical, and I
don't see what else could be passed into it. We literally don't _have_
anythign else than the pte.

But the ppc architecture could easily decide to walk the hash tables and
invalidate in ptep_test_and_clear_young(). And if it ends up being a
performance issue, it _appears_ that all users of "page_referenced()" 
(which is the only thing that does this) are actually using the return 
value as just a boolean. And it's entirely possible that we should break 
out of "page_referenced()" on the _first_ hit of "yes, this has been 
referenced".

That would make it much less CPU-intensive to make
"ptep_test_and_clear_young()" slightly heavier to execute. It would also 
cause "page_referenced()" to not clear _all_ mapped reference bits at the 
same time - which might unfairly cause multi-used pages to stay in memory. 
On the other hand, that might be the _right_ behaviour.

Rik? Andrea? 

Worth testing, perhaps.

		Linus
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