From owner-freebsd-hackers Wed Jan 6 20:23:31 1999 Return-Path: Received: (from majordom@localhost) by hub.freebsd.org (8.8.8/8.8.8) id UAA29652 for freebsd-hackers-outgoing; Wed, 6 Jan 1999 20:23:31 -0800 (PST) (envelope-from owner-freebsd-hackers@FreeBSD.ORG) Received: from iquest3.iquest.net (iquest3.iquest.net [209.43.20.203]) by hub.freebsd.org (8.8.8/8.8.8) with SMTP id UAA29615 for ; Wed, 6 Jan 1999 20:23:20 -0800 (PST) (envelope-from toor@y.dyson.net) Received: (qmail 9487 invoked from network); 7 Jan 1999 04:22:49 -0000 Received: from dyson.iquest.net (HELO y.dyson.net) (198.70.144.127) by iquest3.iquest.net with SMTP; 7 Jan 1999 04:22:49 -0000 Received: (from root@localhost) by y.dyson.net (8.9.1/8.9.1) id XAA00697; Wed, 6 Jan 1999 23:22:48 -0500 (EST) Message-Id: <199901070422.XAA00697@y.dyson.net> Subject: Re: questions/problems with vm_fault() in Stable In-Reply-To: <199901070315.UAA10543@usr09.primenet.com> from Terry Lambert at "Jan 7, 99 03:15:21 am" To: tlambert@primenet.com (Terry Lambert) Date: Wed, 6 Jan 1999 23:22:48 -0500 (EST) Cc: dillon@apollo.backplane.com, tlambert@primenet.com, dyson@iquest.net, pfgiffun@bachue.usc.unal.edu.co, freebsd-hackers@FreeBSD.ORG From: "John S. Dyson" Reply-To: dyson@iquest.net X-Mailer: ELM [version 2.4ME+ PL38 (25)] MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: owner-freebsd-hackers@FreeBSD.ORG Precedence: bulk X-Loop: FreeBSD.ORG Terry Lambert said: > > I'm not trying to 'type' a VFS layer. The problem is that some > idiot (who was right) thought it's be faster to implement block > access in FS's that need block access, instead of creating a generic > "stream tail" that implemented the buffer cache interface. > > If they had done that, then the VOP_GETPAGES/VOP_PUTPAGES would > directly access the VOP_GETBLOCKRANGE/VOP_PUTBLOCKRANGE of the > underling tail, and FFS could stack on top of it, and "stack" > on top of other FS's (although it would only use a subset of > the operations, which would pretty much result in it doing the > same thing as if it wasn't stacked, unless you implemented > VOP_GETBLOCKRANGE/VOP_PUTBLOCKRANGE, for example to implement > "vinum" as a stacking layer). > Lots of I/O doesn't require explicit system calls (but are faults.) When mixing layering and coherent mmaps, the VFS paradigm is just not very useful. VFS as it is supports a subset of what is needed for coherency (except if lots of invalidates are passed, and even then there are problems.) If you can show where a memory coherency mechanism (like MESI) is provided inside of the VFS, then it might be possible. I cannot see it though. VFS supporting simple read/write type system calls is really different than distributed memory schemes (and coherent mmap capabilities are very similar and analogous.) -- John | Never try to teach a pig to sing, dyson@iquest.net | it makes one look stupid jdyson@nc.com | and it irritates the pig. To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-hackers" in the body of the message