From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752210Ab2IPVtR (ORCPT ); Sun, 16 Sep 2012 17:49:17 -0400 Received: from cantor2.suse.de ([195.135.220.15]:43096 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751186Ab2IPVtQ (ORCPT ); Sun, 16 Sep 2012 17:49:16 -0400 Date: Sun, 16 Sep 2012 23:49:12 +0200 From: Jan Kara To: OGAWA Hirofumi Cc: Jan Kara , Fengguang Wu , viro@zeniv.linux.org.uk, hch@lst.de, linux-kernel@vger.kernel.org Subject: Re: [PATCH] Fix queueing work if !bdi_cap_writeback_dirty() Message-ID: <20120916214912.GA7503@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> <20120914131952.GA4952@quack.suse.cz> <87ipbgn2gz.fsf@devron.myhome.or.jp> <20120914144543.GB4952@quack.suse.cz> <878vccmygy.fsf@devron.myhome.or.jp> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <878vccmygy.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 Sat 15-09-12 00:10:53, OGAWA Hirofumi wrote: > Jan Kara writes: > > >> If flusher is working, it clears dirty flags of inode. But if those > >> handers can't flush at the time, we have to do redirty or something to > >> prevent the reclaim. > > Well, if this is your only problem then I'd see better options than just > > disabling flusher thread. If the inability to write inode is rare, then > > redirtying seems like a reasonable option (despite I agree it's a bit > > ugly). If the inability to write is common, then you'll probably have to do > > the dirty inode tracking yourself in some list and expose inodes to VM when > > they are ready to be written. Or you handle writing of inodes yourself but > > leave writing of pages on flusher thread... > > Basically all data can be data-integrity write like data logging, so it > would be more than common. And ->writepages() will also ignore WBC_SYNC_NONE. > > > Because when you disable flusher thread completely you have to put all the > > smarts to avoid livelocks, keep fairness among processes, write old data, > > keep number of dirty pages under control into your filesystem which leads > > to a lot of duplication. > > I'm not sure what you meant though. What is the difference with ignoring > WBC_SYNC_NONE? When you completely ignore WB_SYNC_NONE writeback, you'll soon drive the machine close to dirty limits and processes dirtying pages will get throttled. Because flusher threads won't be able to write pages - they do WB_SYNC_NONE writeback when we have too many dirty pages - processes will be throttled until somebody calls sync(1) or someone writes the data for some other reason... So I suspect things won't really work as you expect. Honza -- Jan Kara SUSE Labs, CR