Date: Wed, 6 Jan 1999 23:22:48 -0500 (EST) From: "John S. Dyson" <dyson@iquest.net> To: tlambert@primenet.com (Terry Lambert) Cc: dillon@apollo.backplane.com, tlambert@primenet.com, dyson@iquest.net, pfgiffun@bachue.usc.unal.edu.co, freebsd-hackers@FreeBSD.ORG Subject: Re: questions/problems with vm_fault() in Stable Message-ID: <199901070422.XAA00697@y.dyson.net> In-Reply-To: <199901070315.UAA10543@usr09.primenet.com> from Terry Lambert at "Jan 7, 99 03:15:21 am"
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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
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