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Date:      Sat, 28 Dec 1996 18:59:56 -0800
From:      David Greenman <dg@root.com>
To:        brian@mediacity.com
Cc:        freebsd-smp@freebsd.org
Subject:   Re: A question of how much memory? 
Message-ID:  <199612290259.SAA02634@root.com>
In-Reply-To: Your message of "Sat, 28 Dec 1996 17:15:53 PST." <19961229011553.25152.qmail@mediacity.com> 

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>I have an ASUS 2xPP200 with 256MB.  It has been my guess that
>I therefore need to set MAXMEM to 128*1024, assuming each
>processor has its own private 128MBs to work with.  This does
>indeed work.
>
>However, my assumptions may be wrong, and memory may be shared
>in some way.  In which case MAXMEM may need to by 256*1024.
>I've tried this and the kernel fails to boot with a Panic
>message along the lines of unable to [reach/allocate?] bounce
>buffer.
>
>Basically, which is it supposed to work?

   You're correct that your assumption is wrong. All of the memory is shared
in SMP PCs. The reason the machine panics is because you have run out of
kernel virtual memory. You need to more carefully tune the various parameters
in your kernel config file (the ones that take lots of virtual memory like
NMBCLUSTERS). The fact that it doesn't panic with 128MB indicates that you
are right on the edge of running out and the extra kernel data structures
that are allocated to manage 256MB is just enough to run out.
   BTW, why do you have bounce buffers configured in your kernel??

-DG

David Greenman
Core-team/Principal Architect, The FreeBSD Project



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