From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753534AbZIOM65 (ORCPT ); Tue, 15 Sep 2009 08:58:57 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1753376AbZIOM6y (ORCPT ); Tue, 15 Sep 2009 08:58:54 -0400 Received: from cantor.suse.de ([195.135.220.2]:40898 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753224AbZIOM6y (ORCPT ); Tue, 15 Sep 2009 08:58:54 -0400 Date: Tue, 15 Sep 2009 14:58:55 +0200 From: Jan Kara To: Jens Axboe Cc: Jan Kara , Christoph Hellwig , linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, chris.mason@oracle.com, tytso@mit.edu, akpm@linux-foundation.org, trond.myklebust@fys.uio.no Subject: Re: [PATCH 6/7] writeback: separate starting of sync vs opportunistic writeback Message-ID: <20090915125855.GF12169@duck.suse.cz> References: <1252920994-11141-1-git-send-email-jens.axboe@oracle.com> <1252920994-11141-7-git-send-email-jens.axboe@oracle.com> <20090914133307.GJ24075@duck.suse.cz> <20090914134207.GA14830@infradead.org> <20090914192803.GL14984@kernel.dk> <20090914194242.GM14984@kernel.dk> <20090915090847.GA12169@duck.suse.cz> <20090915091402.GG23126@kernel.dk> <20090915114426.GJ23126@kernel.dk> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20090915114426.GJ23126@kernel.dk> User-Agent: Mutt/1.5.17 (2007-11-01) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue 15-09-09 13:44:26, Jens Axboe wrote: > On Tue, Sep 15 2009, Jens Axboe wrote: > > On Tue, Sep 15 2009, Jan Kara wrote: > > > On Mon 14-09-09 21:42:43, Jens Axboe wrote: > > > > On Mon, Sep 14 2009, Jens Axboe wrote: > > > > > On Mon, Sep 14 2009, Christoph Hellwig wrote: > > > > > > On Mon, Sep 14, 2009 at 03:33:07PM +0200, Jan Kara wrote: > > > > > > > On Mon 14-09-09 11:36:33, Jens Axboe wrote: > > > > > > > > bdi_start_writeback() is currently split into two paths, one for > > > > > > > > WB_SYNC_NONE and one for WB_SYNC_ALL. Add bdi_sync_writeback() > > > > > > > > for WB_SYNC_ALL writeback and let bdi_start_writeback() handle > > > > > > > > only WB_SYNC_NONE. > > > > > > > What I don't like about this patch is that if somebody sets up > > > > > > > writeback_control with WB_SYNC_ALL mode set and then submits it to disk via > > > > > > > bdi_start_writeback() it will just silently convert his writeback to an > > > > > > > asynchronous one. > > > > > > > So I'd maybe leave setting of sync_mode to the caller and just WARN_ON if > > > > > > > it does not match the purpose of the function... > > > > > > > > > > > > Or initialize the wb entirely inside these functions. For the sync case > > > > > > we really only need a superblock as argument, and for writeback it's > > > > > > bdi + nr_pages. And also make sure they consistenly return void as > > > > > > no one cares about the return value. > > > > > > > > > > Yes, I thought about doing that and like that better than the warning. > > > > > Just pass in the needed args and allocate+fill the wbc on stack. I'll > > > > > make that change. > > > > > > > > That works out much better, imho: > > > > > > > > http://git.kernel.dk/?p=linux-2.6-block.git;a=commit;h=270c12655d7d11e234d335a8ab0540c02c034b66 > > > Yeah, the code looks better. BTW, how about converting also > > > bdi_writeback_all() to get superblock and nr_pages as an argument? > > > Currently it seems to be the only place "above" flusher thread which uses > > > wbc and it's just constructed in the callers of bdi_writeback_all() and > > > then disassembled inside the function... > > > > Yes good point, I'll include that too. Thanks! > > One small problem there, though... Currently all queued writeback is > range cyclic, however with this change then we drop that bit from > sync_inodes_sb() which isn't range_cyclic and instead just specifies the > whole range. I'm not sure I understand your comment but I see a problem that even writeback queued from sync_inodes_sb() is processed by wb_writeback() which sets range_cyclic. That's a bug even in your old patchset. Let's have a look at the flags in wbc: nonblocking - Currently only set by direct callers of ->writepage() BUT originally wb_kupdate() and background_writeout() also set this flag. Since filesystems and write_cache_pages() use the flag we should set it for equivalent writeouts as well. This should be fixed... encountered_congestion - Checked only by AFS, probably we can get rid of it now. for_kupdate - Used, we set it properly in wb_writeback() so that is fine. for_reclaim - Used by direct callers of ->writepage(). OK. for_writepages - Only set. Get rid of it. range_cyclic - Used. Set also when a caller didn't want it - should be fixed. Honza -- Jan Kara SUSE Labs, CR