Date: Wed, 23 Dec 1998 18:24:01 -0500 (EST) From: "John S. Dyson" <dyson@iquest.net> To: pfgiffun@bachue.usc.unal.edu.co (Pedro F. Giffuni) Cc: freebsd-hackers@FreeBSD.ORG Subject: Re: questions/problems with vm_fault() in Stable Message-ID: <199812232324.SAA26271@y.dyson.net> In-Reply-To: <367F9D58.D755DAB0@bachue.usc.unal.edu.co> from "Pedro F. Giffuni" at "Dec 22, 98 08:23:36 am"
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Pedro F. Giffuni said: > In this thread I've heard good comment on UVM and also that there is not > anyone really in charge of the VM. > > Would this indicate that we want UVM ?? Chuck Cranor's papers say a port > could be done but, as I understand, our VM is faster. > In *no way* is UVM done. It is still missing merged VM buffer cache and is not productized (from a performance standpoint.) As the optimizations for performance are done, the complexities also arise. From a tutorial standpoint, UVM might be good because of it's cleanliness -- however the performance is the critical thing that distinguishes FreeBSD from the alternatives. Almost any negative allegations as to portability regarding the FreeBSD VM are incorrect and mostly spin. There are features in the FreeBSD VM that take advantage of CPU capabilities that are inherently non-portable. However, those features are optional, and not necessary for correct operation. I suspect that as the Alpha platform is optimized, the VM code will be tuned to support that super-well also. Geesh, there is already support in FreeBSD for non-copy read/write to/from the buffer cache also. It isn't complete, but is there. It only takes someone to finish the job (which I was in the middle of.) On some machines, that feature would definitely be a mis-feature, but on the X86, it would be useful. Also, the FreeBSD VFS/VM code already supports the ability to have non-mapped buffers (and has for 2years.) There is alot in there that might make the complexity look excessive, but that is only because there are features in there that are almost ready to go. I suspect that if there is a concentrated effort on UVM for a couple of years, by a couple of people, it will be as functional as FreeBSD VM. At that point, it might be worthwhile to adopt it. For an opinion about using a FreeBSD VM vs. a UVM development environment -- use both for awhile, and then notice the very significant (noticible) differences in performance. -- 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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