Date: Thu, 19 Aug 1999 20:10:57 -0700 From: Chuck Silvers <chuq@chuq.com> To: Terry Lambert <tlambert@primenet.com> Cc: wrstuden@nas.nasa.gov, Hackers@FreeBSD.ORG, fs@FreeBSD.ORG Subject: Re: BSD XFS Port & BSD VFS Rewrite Message-ID: <19990819201057.A2185@chuq.chuq.com> In-Reply-To: <199908182043.NAA28863@usr06.primenet.com>; from Terry Lambert on Wed, Aug 18, 1999 at 08:43:14PM %2B0000 References: <Pine.SOL.3.96.990818112953.14430G-100000@marcy.nas.nasa.gov> <199908182043.NAA28863@usr06.primenet.com>
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On Wed, Aug 18, 1999 at 08:43:14PM +0000, Terry Lambert wrote: > > > > Nope. The problem is that while stacking (null, umap, and overlay fs's) > > > > work, we don't have the coherency issues worked out so that upper layers > > > > can cache data. i.e. so that the lower fs knows it has to ask the uper > > > > layers to give pages back. :-) But multiple ls -lR's work fine. :-) > > > > > > With UVM in NetBSD, this is (supposedly) not an issue. > > > > UBC. UVM is a new memory manager. UBC unifies the buffer cache with the VM > > system. > > I was under the impression that th "U" in "UVM" was for "Unified". > > Does NetBSD not have a unified VM and buffer cache? is th "U" in > "UVM" referring not to buffer cache unification, but to platform > unification? > > It was my understanding from John Dyson, who had to work on NetBSD > for NCI, that the new NetBSD stuff actually unified the VM and the > buffer cache. > > If this isn't the case, then, yes, you will need to lock all the way > up and down, and eat the copy overhead for the concurrency for the > intermediate vnodes. 8-(. netbsd w/UVM currently doesn't have unified caches. that feature is what I named UBC, for "unified buffer cache" (ala DEC's UBC). the U in UVM doesn't actually stand for anything. :-) > > > You could actually think of it this way, as well: only FS's that > > > contain vnodes that provide backing should implement VOP_GETPAGES > > > and VOP_PUTPAGES, and all I/O should be done through paging. > > > > Right. That's part of UBC. :-) > > Yep. Again, if NetBSD doesn't have this, it's really important > that it obtain it. 8-(. I'm workin' on it... it'll go in soon after the branch for the next release is created (ie. it won't be in the next release, but the one after that). -Chuck To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-hackers" in the body of the message
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