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Date: Wed, 02 Sep 2009 18:46:46 +0300
From: Alexander Motin <mav@FreeBSD.org>
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To: Mel Flynn <mel.flynn+fbsd.current@mailing.thruhere.net>
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Cc: "Derek \(freebsd lists\)" <482254ac@razorfever.net>,
	freebsd-current@freebsd.org
Subject: Re: MAXPHYS and physical memory (Was: Re: siis/atacam/ata/gmirror
 8.0-BETA3 disk performance)
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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