What's a "tahoe"? --- and the new bsd kernel memory allocator

[Malaclypse the Elder]

In article <3259 at leo.UUCP>, jack at leo.UUCP ( Jack Benkual) writes:
> In article <3420 at phri.UUCP>, roy at phri.UUCP (Roy Smith) writes:
> > 
> > 	For months I've been listening to people talking about "4.3-tahoe"
> > but I still havn't seen anybody explain what a "tahoe" is.
> > -- 
> 
> Tahoe was the project name for the CCI Power 6/32 Superminicomputer available
> since 1985. It has an architecture very similar to VAX/780 and probably that
> and the higher performance (8 VAX MIPS in 1985) was the reason that Berkeley
> released 4.3-Tahoe.

does the tahoe have a more limited kernel address space than the vax?
the reason i ask is that at the recent usenix conference in san francisco,
kirk mckusick presented the architecture of the new kernel memory allocator
for bsd.  it turns out that for memory requests smaller than a page or two,
they do allocation based on a power of 2 scheme (not really a binary buddy
system since they do not do coalescing).  but for memory requests larger
than a page or two, they do something like a first fit (i don't remember
exactly what).

since the primary disadvantage of a power of 2 scheme is internal memory
fragmentation, i asked why, for large allocations, they did not implement
a buddy scheme (or their power of 2 scheme) to allocate kernel virtual
address space and simply allocate the minimal amount of physical pages
necessary to satisfy the request.  that way, you have the fast allocation
of the buddy system with minimal fragmentation of physical memory resources.
(also thrown in are kernel traps in case you ever use much more than you
asked for).

the response i got from him was that not only was it not desirable to
have internal fragmentation of physical memory but there were systems
with limited kernel address space and that it was undesirable to have
fragmentation of virtual address space.  since all the modern processors
that i know of (not many) have address spaces of at least 4Gbytes with
at least 1/4 going to kernel, i did not think this was an issue.

now i learn of this tahoe processor which the bsd distribution is based
on.  is this the system he had in mind when he said that there are
processors with limited kernel address space?  more importantly, should
one design a system that is going to be ported to many processors based
on such a restriction?

danny chen
att!homxc!dwc