Date: 15 Feb 2007 16:42:48 +0100 From: Tomas Olsson <tol@it.su.se> To: Robert Watson <rwatson@FreeBSD.org> Cc: freebsd-fs@FreeBSD.org, arla-drinkers@stacken.kth.se Subject: Re: Arla on FreeBSD Message-ID: <lsr4ppn5sw7.fsf@kashyyyk.ite.kth.se> In-Reply-To: <20070215150015.O90799@fledge.watson.org> References: <20070214162938.GA96725@keira.kiwi-computer.com> <20070214173211.L1054@chrishome.localnet> <20070214170808.GC96725@keira.kiwi-computer.com> <lsrvei45pq1.fsf@kashyyyk.ite.kth.se> <20070215044707.GA39168@deviant.kiev.zoral.com.ua> <lsrmz3f680v.fsf_-_@kashyyyk.ite.kth.se> <20070215104537.GC39168@deviant.kiev.zoral.com.ua> <lsrhctn6393.fsf@kashyyyk.ite.kth.se> <20070215120855.GE39168@deviant.kiev.zoral.com.ua> <lsrd54b603c.fsf@kashyyyk.ite.kth.se> <20070215134608.GG39168@deviant.kiev.zoral.com.ua> <lsr8xez5v15.fsf@kashyyyk.ite.kth.se> <20070215150015.O90799@fledge.watson.org>
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Robert Watson <rwatson@FreeBSD.org> writes: > On Thu, 15 Feb 2007, Tomas Olsson wrote: > >> Also, you could look at file handle API, that would save you of path > >> lookups after the vnode is looked up first time (look around for vfs_vptofh > >> and vfs_fhtovp ops). This API is used by NFS server, so it shall work :). > >> > > That's an idea. We used that before in another context, but then we ran into > > trouble with too many OSes so we dropped it. Depends on how much code one > > can share. > > It has been ages since I looked at the xfs/nnpfs internals, but I thought it > already used file handles to identify cache files to the kernel? I seem to > recall several of our fh*() system calls were added by Assar specifically in > support of Arla work. > Sounds likely. I first saw it from arlad's side, so I've always thought of it as an optimization to avoid lookups in that end without pondering it all that much. > Is it the case that one file visible in /afs may now be backed by pages > coming from different cache files? > Yup. There ware requests for low latency fetching of ID3 tags etc, and working with files larger than the cache. > How does this interact with the vnode pager? I assume you actually end > up with two pagers -- one for the file as visible in /afs, and then > satisfy the pager's VOP requests by forwarding them to the right one of > the cache vnodes? > Exactly. As always, just more fine grained. > I trust you don't mmap the cache vnode, which would lead to cache > consistency issues between any mappings of the /afs vnode vs the cache > vnode? > Me too :-) But this is still a suboptimal world where we end up with double pager layers, and consistency can still be a problem. In the long term it would be nice to have arlad open it's cache nodes through nnpfs, be it small files or just one large VM space. > Any chance we could attract you to BSDCan to meet in person to discuss this? > Chance, not probable; May is beyond my horizon. And I do expect to have the arla working properly on fbsd well before that. /t
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