From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jan Kara Subject: Re: [PATCH v3 3/5] mm: Notify filesystems when it's time to apply a deferred cmtime update Date: Tue, 20 Aug 2013 18:00:57 +0200 Message-ID: <20130820160057.GC2862@quack.suse.cz> References: <20130820023615.GE6023@dastard> <20130820040814.GH6023@dastard> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Cc: Theodore Ts'o , Dave Hansen , "linux-kernel@vger.kernel.org" , xfs@oss.sgi.com, Christoph Hellwig , Jan Kara , "linux-ext4@vger.kernel.org" , Tim Chen To: Andy Lutomirski Return-path: Content-Disposition: inline In-Reply-To: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: xfs-bounces@oss.sgi.com Sender: xfs-bounces@oss.sgi.com List-Id: linux-ext4.vger.kernel.org On Mon 19-08-13 21:14:44, Andy Lutomirski wrote: > >> I could require ->writepages *and* ->flush_cmtime to handle the time > >> update, but that would complicate non-transactional filesystems. > >> Those filesystems should just flush cmtime at the end of writepages. > > > > do_writepages() is the wrong place to do such updates - we can get > > writeback directly through .writepage, so the time updates need to > > be in .writepage. That first .writepage call will clear the bit on > > the mapping, so it's only done on the first call to .writepage on > > the given mapping. > > Last time I checked, all the paths that actually needed the timestamp > update went through .writepages. I'll double-check. kswapd can call just .writepage to do the writeout so timestamp update should be handled there as well. Otherwise all pages in a mapping can be cleaned without timestamp being updated. Which btw made me realize that even your scheme doesn't completely make sure timestamp is updated after mmap write - if you have pages 0 and 1, you write to both of them - CMTIME flag gets set. Then fsync_range(fd, 0, 4096) is called. We write the page 0, writeprotect it, update timestamps. But page 1 is still writeable so writes to it won't set CMTIME flag, neither update the timestamp... Not that I think this can be reasonably solved but it is a food for thought. Honza -- Jan Kara SUSE Labs, CR _______________________________________________ xfs mailing list xfs@oss.sgi.com http://oss.sgi.com/mailman/listinfo/xfs