From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752240Ab2INNT5 (ORCPT ); Fri, 14 Sep 2012 09:19:57 -0400 Received: from cantor2.suse.de ([195.135.220.15]:52331 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751008Ab2INNTz (ORCPT ); Fri, 14 Sep 2012 09:19:55 -0400 Date: Fri, 14 Sep 2012 15:19:52 +0200 From: Jan Kara To: OGAWA Hirofumi Cc: Fengguang Wu , viro@zeniv.linux.org.uk, jack@suse.cz, hch@lst.de, linux-kernel@vger.kernel.org Subject: Re: [PATCH] Fix queueing work if !bdi_cap_writeback_dirty() Message-ID: <20120914131952.GA4952@quack.suse.cz> References: <87wr002z39.fsf@devron.myhome.or.jp> <20120913063906.GA24974@localhost> <871ui6e4tl.fsf@devron.myhome.or.jp> <20120914111429.GA19509@localhost> <87r4q4n6r1.fsf@devron.myhome.or.jp> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <87r4q4n6r1.fsf@devron.myhome.or.jp> User-Agent: Mutt/1.5.20 (2009-06-14) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri 14-09-12 21:12:02, OGAWA Hirofumi wrote: > Fengguang Wu writes: > >> >> @@ -120,6 +120,9 @@ __bdi_start_writeback(struct backing_dev > >> >> { > >> >> struct wb_writeback_work *work; > >> >> > >> >> + if (!bdi_cap_writeback_dirty(bdi)) > >> >> + return; > >> > > >> > Will someone in the current kernel actually call > >> > __bdi_start_writeback() on a BDI_CAP_NO_WRITEBACK bdi? > >> > > >> > If the answer is no, VM_BUG_ON(!bdi_cap_writeback_dirty(bdi)) looks better. > >> > >> I guess nobody call it in current kernel though. Hmm.., but we also have > >> check in __mark_inode_dirty(), nobody should be using it, right? > >> > >> If we defined it as the bug, I can't see what BDI_CAP_NO_WRITEBACK wants > >> to do actually. We are not going to allow to disable the writeback task? > > > >> I was going to use this to disable writeback task on my developing FS... > > > > That sounds like an interesting use case. Can you elaborate a bit more? > > > > Note that even if you disable __bdi_start_writeback() here, the kernel > > may also start writeback in the page reclaim path, the fsync() path, > > and perhaps more. > > page reclaim and fsync path have FS handler. So, FS can control those. > > The modern FS have to control to flush carefully. Many FSes are already > ignoring if wbc->sync_mode != WB_SYNC_ALL (e.g. ext3_write_inode, > nilfs_writepages), and have own FS task to flush. Out of curiosity, what exactly do you need to control in your filesystem that makes flusher thread unusable for you? You still have a lot of flexibility with ->write_inode() and ->writepages() callbacks... Honza -- Jan Kara SUSE Labs, CR