From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from relay.sgi.com (relay3.corp.sgi.com [198.149.34.15]) by oss.sgi.com (Postfix) with ESMTP id 65C9B7F54 for ; Thu, 13 Mar 2014 20:24:02 -0500 (CDT) Received: from cuda.sgi.com (cuda1.sgi.com [192.48.157.11]) by relay3.corp.sgi.com (Postfix) with ESMTP id 05299AC003 for ; Thu, 13 Mar 2014 18:24:01 -0700 (PDT) Received: from imap.thunk.org (imap.thunk.org [74.207.234.97]) by cuda.sgi.com with ESMTP id VNjU4p9YS8FzX5G8 (version=TLSv1 cipher=AES128-SHA bits=128 verify=NO) for ; Thu, 13 Mar 2014 18:23:56 -0700 (PDT) Date: Thu, 13 Mar 2014 21:23:00 -0400 From: Theodore Ts'o Subject: Re: [PATCH] fs: push sync_filesystem() down to the file system's remount_fs() Message-ID: <20140314012300.GA8282@thunk.org> References: <20140313073936.GA14663@infradead.org> <1394720456-16629-1-git-send-email-tytso@mit.edu> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: List-Id: XFS Filesystem from SGI List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Errors-To: xfs-bounces@oss.sgi.com Sender: xfs-bounces@oss.sgi.com To: Steve French Cc: jfs-discussion@lists.sourceforge.net, Jan Kara , Anders Larsen , cluster-devel@redhat.com, linux-mtd@lists.infradead.org, Mikulas Patocka , Petr Vandrovec , codalist@TELEMANN.coda.cs.cmu.edu, "linux-cifs@vger.kernel.org" , linux-fsdevel@thunk.org, Christoph Hellwig , Ext4 Developers List , Evgeniy Dushistov , Kees Cook , fuse-devel@lists.sourceforge.net, reiserfs-devel@vger.kernel.org, xfs@oss.sgi.com, linux-nilfs@vger.kernel.org, OGAWA Hirofumi , "linux-nfs@vger.kernel.org" , Artem Bityutskiy , linux-ntfs-dev@lists.sourceforge.net, samba-technical , Adrian Hunter , linux-f2fs-devel@lists.sourceforge.net, ocfs2-devel@oss.oracle.com, linux-fsdevel , Phillip Lougher , linux-btrfs@vger.kernel.org On Thu, Mar 13, 2014 at 07:33:02PM -0500, Steve French wrote: > On Thu, Mar 13, 2014 at 9:20 AM, Theodore Ts'o wrote: > > Previously, the no-op "mount -o mount /dev/xxx" operation when the > > file system is already mounted read-write causes an implied, > > unconditional syncfs(). This seems pretty stupid, and it's certainly > > documented or guaraunteed to do this, nor is it particularly useful, > > except in the case where the file system was mounted rw and is getting > > remounted read-only. > > Is there a case where a file system, not mounted read-only, > would want to skip the syncfs on remount? I don't know > of any particular reason to do a syncfs on remount unless > caching behavior is changing (or moving to read-only mount), > but if as you say it is documented and guaranteed... If the file system is mounted read-write, and it is transitioning to read-only, i.e. "mount -o remount,ro /" then you do want to write out all dirty data before you transition it to be read-only (otherwise you would lose data). It is my belief that this is the _only_ data integrity issue which is implied by remount (and this is more about not losing work done by previous system calls). The background reason for this commit is that a user complained on the ext4 list that he is using containers in a virtualization environment, and due to the init scripts which the user doesn't want to change, it is causing gazillions of no-op remounts, and this is causing ext4 (and xfs) to do send CACHE FLUSH commands because it is required by the syncfs(2) system call, which also calls sync_filesystem. These CACHE FLUSH commands are unneeded for anything, especially for these no-op remounts, and so I want them to go away for remounts, but they should still be there in response to syncfs(2) requests. Cheers, - Ted _______________________________________________ xfs mailing list xfs@oss.sgi.com http://oss.sgi.com/mailman/listinfo/xfs