From mboxrd@z Thu Jan 1 00:00:00 1970 From: Christoph Hellwig Subject: Re: do_sync() and XFSQA test 182 failures.... Date: Fri, 31 Oct 2008 18:22:32 -0400 Message-ID: <20081031222232.GB29761@infradead.org> References: <20081030085020.GP17077@disturbed> <20081030224625.GA18690@infradead.org> <20081031001249.GM4985@disturbed> <20081031203123.GA11514@infradead.org> <20081031215430.GB19509@disturbed> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii To: Christoph Hellwig , xfs@oss.sgi.com, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org Return-path: Content-Disposition: inline In-Reply-To: <20081031215430.GB19509@disturbed> Sender: linux-kernel-owner@vger.kernel.org List-Id: linux-fsdevel.vger.kernel.org On Sat, Nov 01, 2008 at 08:54:30AM +1100, Dave Chinner wrote: > Effectively, yes. > > Currently we iterate inodes for data and "metadata" sync, and the > only other concept is writing superblocks. I think most filesystems > have more types of metadata than this, so it makes sense for sync to > work on abstracts sync as data and metadata rather than data, inodes > and superblocks... Yes, absolutely. And for those that have inodes as primary / only metadata besides superblock we can still provide a generic_sync_inodes helper that just takes a callback to apply to every inode. Which we probably want anyway as XFS is the only intree-filesystem that currently has a more efficient way to iterate inodes. > > And as we found out it's not just sync that gets it wrong, it's also > > fsync (which isn't part of the above picture as it's per-inode) that > > gets this utterly wrong, as well as all kinds of syncs, not just the > > unmount one. > > Async writeback (write_inode()) has the same problem as fsync - > writing the inode before waiting for data I/O to complete - which > means we've got to jump through hoops in the filesystem to avoid > blocking on inodes that can't be immediately flushed, and often we > end up writing the inode multiple times and having to issue log > forces whenw e shouldn't need to. Effectively we have to tell the > VFS to "try again later" the entire time data is being flushed > before we can write the inode and it's exceedingly inefficient..... Yes, that was the couple of sync functions I meant above as the whole inode writeback path is extremly convoluted - mostly due to the dirty data vs metadata mixup mess.