On Tue, Jun 21, 2005 at 10:02:44AM +1000, matthew green wrote:
>    
>    > IIRC, some ports don't call uvm_pageidlezero as it's considered harmful.
>    
>    Why? Cache poisoning?
> 
> 
> it also interfered with UBC when it arrived.  enable it and run some
> tests and see if it works better for you :-)

I've had it on in my test environment for a couple years now, I think.
I meant to go check if it had any discernable negative impact anymore,
but, uh, I forgot.   the problem before was that we were mapping the
page to be zeroed with an uncached mapping, which slowed down DMA a lot.
now we use a cached mapping, so the problem (if there is one) will be
excessive cache flushing instead.  it'd be nice if someone looked into this.

-Chuck