Re: AGP and PAT (induced?) problem (on AMD family 6)

[Rene Herman <rene.herman@keyaccess.nl>]

On 20-08-08 21:41, Venki Pallipadi wrote:

> OK. I have reproduced this list size issue locally and this order 1 
> allocation and set_memory_uc on that allocation is actually coming
> from agp_allocate_memory() -> agp_generic_alloc_page() ->
> map_page_into_agp() agp_allocate_memory breaks higher order page
> requests into order 1 allocs.
> 
> On my system I see multiple agp_allocate_memory requests for nrpages 
> 8841, 1020, 16, 2160, 2160, 8192. Together they end up resulting in 
> more than 22K entries in PAT pages.

Okay, thanks for the confirmation.

Now, how to fix...

Firstly, it seems we can conclude that any expectancy of a short PAT 
list is simply destroyed by AGP. I believe the best thing migh be to 
look into "fixing" AGP rather than PAT for now?

In a sense the entire purpose of the AGP GART is collecting non 
contiguous pages but given that in practice it's generally still just 
one or at most a few regions, going to multi-page allocs sounds most 
appetising to me.

All in tree AGP drivers except sgi-agp use agp_generic_alloc_page(), ali 
via m1541_alloc_page and i460 via i460_alloc_page.

Rene.