Date: Sun, 25 Jan 1998 23:47:31 +0000 (GMT) From: Terry Lambert <tlambert@primenet.com> To: dyson@FreeBSD.ORG Cc: scottm@cs.ucla.edu, freebsd-current@FreeBSD.ORG Subject: Re: stable current? Message-ID: <199801252347.QAA17876@usr02.primenet.com> In-Reply-To: <199801251803.NAA25960@dyson.iquest.net> from "John S. Dyson" at Jan 25, 98 01:03:42 pm
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> > For UNI kernels, John's latest round of vm changes seem to be more > > stable -- OTOH I'm not really pushing things that hard either. > > Rather than announcing the system is "better", I have been holding > out until someone else sees it. The only thing(s) that shouldn't > be working are the layered filesystems. Those thing(s) are really > broken, and absolutely no Lite/2 derivative has them working properly. > > Because of the structure of the merged VM/Buffer cache, we haven't had them > working for, a long time but now at least we have a better chance of someone > fixing them. That's not the only problem; I've identified most of them at one time or another... Were you out here (Bay Area) last Thursday for McKusick's talk at Network Appliance on FS stacking? I didn't go to that one, but I talked to him for about half an hour about a month ago, and he seemed to agree with most of what I identified (plus added a thing or two that I hadn't thought of before). The single biggest problem has *got* to be alias buffers hung off top and bottom vnodes in a stack. The vop_getpages/vop_putpages interface needs to become mandatory for all FS's. No more sneaking around it in the vnode pager. That should solve most of the nullfs and single-layer stack FS problems up front, so long as you don't expect locking to work. A real fix will require a VOP to ask for the backing vnode where the buffers and locks are hung off of; until then, I don't think unionfs has a chance of being safe to use. Terre Lambert terry@lambert.org --- Any opinions in this posting are my own and not those of my present or previous employers.
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