From mboxrd@z Thu Jan 1 00:00:00 1970 From: Trond Myklebust Subject: Re: [RFC PATCH]autofs4: hang and proposed fix Date: Wed, 30 Nov 2005 12:04:11 -0500 Message-ID: <1133370251.8625.38.camel@lade.trondhjem.org> References: <20051116101740.GA9551@RAM> <438B3C34.2050509@us.ibm.com> <1133219572.27824.24.camel@localhost.localdomain> <438C82FB.50706@us.ibm.com> <1133369361.27824.61.camel@localhost.localdomain> Mime-Version: 1.0 Content-Type: text/plain Content-Transfer-Encoding: 7bit Cc: Ian Kent , "William H. Taber" , Ram Pai , autofs mailing list , linux-fsdevel , Al Viro , smaneesh@in.ibm.com Return-path: Received: from pat.uio.no ([129.240.130.16]:64956 "EHLO pat.uio.no") by vger.kernel.org with ESMTP id S1751460AbVK3REh (ORCPT ); Wed, 30 Nov 2005 12:04:37 -0500 To: Badari Pulavarty In-Reply-To: <1133369361.27824.61.camel@localhost.localdomain> Sender: linux-fsdevel-owner@vger.kernel.org List-Id: linux-fsdevel.vger.kernel.org On Wed, 2005-11-30 at 08:49 -0800, Badari Pulavarty wrote: > On Wed, 2005-11-30 at 09:02 -0500, Ian Kent wrote: > > On Tue, 29 Nov 2005, William H. Taber wrote: > > > > > Ian Kent wrote: > > > > We'll need to do an analysis of all callers of the revalidate method. > > > You are right. Searching through the sources, it would appear that I > > > missed fixing autofs and devfs. Everyone else just defines a revalidate > > > routine but doesn't call one. You may find devfs to be interesting > > > because they have code to determine whether they need to release the > > > i_sem lock or not. I am working on an updated patch to include the > > > changes needed for these two modules. > > > > I've looked at devfs before but that bit of code sounds interesting to me. > > > > The other thing that concerns me is that we may be increasing the latency > > of some code paths that need to be really fast. I was thinking that > > perhaps it might be good to try a change more in line with the locking > > used in link_patch_walk (ie. i_sem free revalidate) rather than that used > > in lookup_one_len. My only justification being that lookup is called to > > create stuff where revalidate is called to check stuff. I've been > > poking around and this change looks fairly difficult as well (I seem to > > remember you also looked at this). > > > > Anyway, I'm keen to have a look at your patch. > > Thanks much for your interest and help. > > > > Ian > > > > Again, I am posting Will's latest patch on his behalf. > > Any thoughts on how acceptable are the VFS changes ? That will slow link_path_walk() for commonly accessed shared directories (/lib, /usr/share,...) down to a crawl. Instead of having lock-free lookups of cached dentries, you are suddenly serialising everybody in the parent directory. Cheers, Trond