Xref: utzoo comp.arch:6037 comp.unix.wizards:10392 Path: utzoo!utgpu!attcan!uunet!husc6!cmcl2!nrl-cmf!ames!ncar!oddjob!gargoyle!att!whuts!homxb!homxc!dwc From: dwc@homxc.UUCP (Malaclypse the Elder) Newsgroups: comp.arch,comp.unix.wizards Subject: Re: What's a "tahoe"? --- and the new bsd kernel memory allocator Message-ID: <2991@homxc.UUCP> Date: 8 Aug 88 21:29:21 GMT References: <6341@bloom-beacon.MIT.EDU> <60859@sun.uucp> <474@m3.mfci.UUCP> <3259@leo.UUCP> Organization: Legion of Dynamic Discord Lines: 45 Summary: In article <3259@leo.UUCP>, jack@leo.UUCP ( Jack Benkual) writes: > In article <3420@phri.UUCP>, roy@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