From mboxrd@z Thu Jan 1 00:00:00 1970 From: David Teigland Subject: Re: File system awareness (or lack thereof) of vfs granting of leases Date: Tue, 20 Feb 2007 15:25:08 -0600 Message-ID: <20070220212508.GD3932@redhat.com> References: <45D6937A.10902@redhat.com> <20070218063948.GC22022@fieldses.org> <20070220190817.GB3932@redhat.com> <38020.141.211.133.169.1172004714.squirrel@www.fieldses.org> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Wendy Cheng , linux-fsdevel@vger.kernel.org To: bfields@fieldses.org Return-path: Received: from mx1.redhat.com ([66.187.233.31]:37534 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1030431AbXBTVWq (ORCPT ); Tue, 20 Feb 2007 16:22:46 -0500 Content-Disposition: inline In-Reply-To: <38020.141.211.133.169.1172004714.squirrel@www.fieldses.org> Sender: linux-fsdevel-owner@vger.kernel.org List-Id: linux-fsdevel.vger.kernel.org On Tue, Feb 20, 2007 at 03:51:54PM -0500, bfields@fieldses.org wrote: > > On Tue, Feb 20, 2007 at 10:46:51AM -0500, Robert Rappaport wrote: > > We did an experimental distributed lease implementation in gfs(1) a while > > ago. It worked, but was so extremely expensive that there was no point in > > considering it seriously. The problem is that _every_ open and close of > > every file requires a new dlm lock operation. Leases require knowledge > > about the cluster-wide opened/closed state of files, not only that but the > > mode they're open in. > > We're using leases to implement NFSv4 delegations. Delegations are > similar to leases--they come in read and write variants, and they give > clients a guarantee that they'll be warned before another client is > allowed to do a conflicting open--but delegations are completely optional. > A server can deny a delegation for any reason, even when there isn't > necessarily a conflicting open. > > So perhaps we need some way for nfsd to ask the filesystem to give it a > lease, but only if it's easy to do so. Would it be possible to make it > cheap for GFS to give out leases in some particular (hopefully common) > cases? I don't know of any shortcuts off hand, but there could certainly be some. Doing something completely different and not using cluster locks may also be worth investigating. Dave