MAXPHYS and physical memory (Was: Re: siis/atacam/ata/gmirror
8.0-BETA3 disk performance)
mav at FreeBSD.org
Wed Sep 2 21:20:53 UTC 2009
Mel Flynn wrote:
> On Wednesday 02 September 2009 17:46:46 Alexander Motin wrote:
>> 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
>> Could you show your panic message?
> It's been a while since I last tried, during 7.1-STABLE. Two different
> machines wouldn't boot, both 1.5G; loading kernel.old, then commenting the
> MAXPHYS change, rebuilding kernel made things work, so I stopped pursuing this
> at the time.
> I remember the panic message quite early page fault, one of the first drivers
> loaded (ahci or acpi). Since this is supposed to work, I'm going to pursue it
> further and see if I can still reproduce it.
I have fixed MAXPHYS issue in ata-ahci in RELENG_8, but I haven't merged
it lower as code is quite different. So it would be nice if you can
check it on 8.x.
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