From mboxrd@z Thu Jan 1 00:00:00 1970 From: Wu Fengguang Subject: Re: [PATCH 01/17] writeback: introduce .tagged_sync for the WB_SYNC_NONE sync stage Date: Fri, 13 May 2011 10:56:08 +0800 Message-ID: <20110513025607.GA8016@localhost> References: <20110512135706.937596128@intel.com> <20110512140030.759385136@intel.com> <20110512224013.GH19446@dastard> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Andrew Morton , Jan Kara , Christoph Hellwig , "linux-fsdevel@vger.kernel.org" , LKML To: Dave Chinner Return-path: Content-Disposition: inline In-Reply-To: <20110512224013.GH19446@dastard> Sender: linux-kernel-owner@vger.kernel.org List-Id: linux-fsdevel.vger.kernel.org On Fri, May 13, 2011 at 06:40:13AM +0800, Dave Chinner wrote: > On Thu, May 12, 2011 at 09:57:07PM +0800, Wu Fengguang wrote: > > sync(2) is performed in two stages: the WB_SYNC_NONE sync and the > > WB_SYNC_ALL sync. Tag the first stage with wbc.tagged_sync and do > > livelock prevention for it, too. > > > > Note that writeback_inodes_sb() is called by not only sync(), they are > > treated the same because the other callers also need livelock prevention. > > > > Impact: It changes the order in which pages/inodes are synced to disk. > > Now in the WB_SYNC_NONE stage, it won't proceed to write the next inode > > until finished with the current inode. > > What about all the filesystems that implement their own > .writepages()/write_cache_pages() functions or have > have special code that checks WB_SYNC_ALL in .writepages (e.g. gfs2, > ext4, btrfs and perhaps others). Don't they all need to be aware of > this tagged_sync field? Right, good point. Currently only ext4 is updated. The other filesystems --- afs, btrfs, cifs, gfs2 --- do not even use PAGECACHE_TAG_TOWRITE for livelock prevention. My plan was to add PAGECACHE_TAG_TOWRITE and tagged_sync code to them as the next step, when tagged_sync is accepted and proved to work fine. Thanks, Fengguang