MAXPHYS and physical memory (Was: Re: siis/atacam/ata/gmirror 8.0-BETA3 disk performance)

[Alexander Motin]

Mel Flynn wrote:
> On Wednesday 02 September 2009 16:51:35 Alexander Motin wrote:
> 
>> For maximum linear I/O performance you may want to build kernel with
>> options 	MAXPHYS=(1024*1024)
> 
> I've found that just doubling the default MAXPHYS already panics-on-boot a 
> 1.5GB i386 system. Is there any reasonable conversion table for MAXPHYS to 
> physical memory, since various memory related kernel setups are derived from 
> or calculated with MAXPHYS?

What especially your panic was about? It could be bug in ATA(4) or some 
other code, that does not handle MAXPHYS correctly. I don't think that 
you could reach memory limit during simple system boot because of that. 
I am successfully running my testing Pentium-75 with 64MB RAM with 1MB 
MAXPHYS.

Could you show your panic message?

-- 
Alexander Motin