From mboxrd@z Thu Jan 1 00:00:00 1970 From: Vladimir V. Saveliev Date: Fri, 29 Feb 2008 17:05:12 +0200 Subject: [Lustre-devel] subtree locks and path re-validation avoidance In-Reply-To: <47BF8FBA.3090705@sun.com> References: <1203080062.19279.91.camel@linux.site> <47BD7D0D.6090906@sun.com> <47BF8FBA.3090705@sun.com> Message-ID: <1204297512.24711.20.camel@linux.site> List-Id: MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: lustre-devel@lists.lustre.org Hello On Fri, 2008-02-22 at 20:15 -0700, Peter J Braam wrote: > I'd like to make a suggestion to perhaps immediately find the right > primitives for getcwd to return a reasonably correct pathname in > Lustre. Peter, would you say a bit more about that: currently, there is nothing a filesystem can do in linux's getcwd. It simply returns instant dcache path from "." to "/". > I believe this is the simplest case where I have seen pathname > revalidation being important. In the context of that example the > subtree lock discussion might gain more clarity. > > I would also like to note that I had a discussion with Linus at one of > the kernel workshops in Ottawa maybe almost 4-5 years ago. First Linus > attacked the idea of using file identifiers - he suggested that doing > everything with pathnames was better (which is what InterMezzo did). > When we explained to him that this requires locking all parents he began > to see the problems we had with this and understood the locking at the > fid/name level that we use in Lustre. I found little resistance when I > mentioned to him that for this model the VFS does not have a correct > implementation of getcwd, unless the dcache is kept current. > > UCSC has received funding from the National Labs and now been turned > into a peta-scale I/O institute I believe did more results on file > systems implemented with pathnames. Some things are beautiful and easy > with pathnames, but others get really ugly, and so far I don't see this > displacing fid ideas that govern NFS, AFS and Lustre. > Best regards, Vladimir