From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Aneesh Kumar K.V" Subject: Re: __fsync_super and inode dirty pages Date: Tue, 5 Aug 2008 23:43:31 +0530 Message-ID: <20080805181331.GA18419@skywalker> References: <20080805175439.GA17772@skywalker> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: "linux-fsdevel@vger.kernel.org" To: Christoph Hellwig , Alexander Viro , Andrew Morton Return-path: Received: from e28smtp05.in.ibm.com ([59.145.155.5]:58052 "EHLO e28esmtp05.in.ibm.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1757977AbYHESNl (ORCPT ); Tue, 5 Aug 2008 14:13:41 -0400 Received: from d28relay02.in.ibm.com (d28relay02.in.ibm.com [9.184.220.59]) by e28esmtp05.in.ibm.com (8.13.1/8.13.1) with ESMTP id m75IDaLD011385 for ; Tue, 5 Aug 2008 23:43:36 +0530 Received: from d28av04.in.ibm.com (d28av04.in.ibm.com [9.184.220.66]) by d28relay02.in.ibm.com (8.13.8/8.13.8/NCO v9.0) with ESMTP id m75IDaj01486986 for ; Tue, 5 Aug 2008 23:43:36 +0530 Received: from d28av04.in.ibm.com (loopback [127.0.0.1]) by d28av04.in.ibm.com (8.13.1/8.13.3) with ESMTP id m75IDa9J007735 for ; Tue, 5 Aug 2008 23:43:36 +0530 Content-Disposition: inline In-Reply-To: <20080805175439.GA17772@skywalker> Sender: linux-fsdevel-owner@vger.kernel.org List-ID: On Tue, Aug 05, 2008 at 11:24:39PM +0530, Aneesh Kumar K.V wrote: > Hi, > > I am trying to understand the expectation on filesystem > writepages by __fsync_super -> generic_sync_sb_inodes call path. > __fsync_super make two calls to generic_sync_sb_inodes and the > second call is made with WB_SYNC_ALL. The problem is, i am finding > multiple ways we may 'break' from the generic_sync_sb_inodes > while (!list_empty(&sb->s_io)) loop. For ex: > > a) When wbc->nr_to_write <=0 > This should normally indicate that we wrote more than we requested > That means we have more dirty pages . So why break from loop ? > This may be ok for nr_to_write limited writeback. But is it ok > for __fsync_super ? > > b) pages_skipped != wbc->pages_skipped. > That means writepages was not able to write some of the pages > and it redirtied the same. We add such inode to s_dirty list. But > we don't loop through the s_dirty list later trying to write the > dirty pages. We actually call generic_sync_sb_inodes again. That > can actually cause s_dirty list content to move to s_io once > via queue_io. But then we can have pages skipped again in the second > call to generic_sync_sb_inodes ? > > > Shouldn't we have a variant that actually loop trough s_dirty and s_more_io > list MULTIPLE times and make sure we force all the dirty pages to disk > before __fsync_super returns ? Or is there an expectation from file > system writepages that would make sure calling generic_sync_sb_inodes > TWICE would guarantee that ? > > The problem I am looking at is listed here. http://thread.gmane.org/gmane.comp.file-systems.ext4/8277 basically a mount -o remount,ro followed by a sync is indicating that there are dirty pages left after remount,ro -aneesh