Re: [PATCH] x86: create array based interface to change page attribute

Arjan van de Ven
2008-03-31T16:10:38Z

Thomas Hellström wrote:

> Let me rehprase. Not really time-critical but it is of some importance
> that CPA is done quickly.
> We're dealing with the tradeoff of reading from uncached device memory

uncached or write combining ?

> vs taking the pages out of
> AGP, setting up a cache-coherent mapping, read and then change back.
> What we'd really would like to set up is a pool of completely unmapped
> (like highmem) pages. Then we could, to a large extent, avoid the CPA
> calls.

changing attributes by nature means a tlb flush and a bunch of expensive cache work.
That's never going to be cheap, I guess it all depends on how much work you do
on the memory for it to pay off or not...