From: Jan Kara Subject: Re: [BUG] aborted ext4 leads to inifinity loop in balance_dirty_pages Date: Wed, 2 Nov 2011 00:13:42 +0100 Message-ID: <20111101231342.GJ18701@quack.suse.cz> References: <4EA6A5E5.2050604@sx.jp.nec.com> <20111025134045.GB8072@quack.suse.cz> <4EAA3EE7.4040802@sx.jp.nec.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Jan Kara , ext4 , Theodore Tso , Andreas Dilger To: Kazuya Mio Return-path: Received: from cantor2.suse.de ([195.135.220.15]:44007 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755183Ab1KAXNp (ORCPT ); Tue, 1 Nov 2011 19:13:45 -0400 Content-Disposition: inline In-Reply-To: <4EAA3EE7.4040802@sx.jp.nec.com> Sender: linux-ext4-owner@vger.kernel.org List-ID: On Fri 28-10-11 14:34:31, Kazuya Mio wrote: > 2011/10/25 22:40, Jan Kara wrote: > > Please no. Generally this boils down to what do we do with dirty data > >when there's error in writing them out. Currently we just throw them away > >(e.g. in media error case) but I don't think that's a generally good thing > >because e.g. admin may want to copy the data to other working storage or > >so. So I think we should rather keep the data and provide a mechanism for > >userspace to ask kernel to get rid of the data (so that we don't eventually > >run OOM). > > I see. I agree with you. > > >>Do you have any ideas? > > So the question is what would you like to achieve. If you just want to > >unblock a thread then a solution would be to make a thread at > >balance_dirty_pages() killable. If generally you want to get rid of dirty > >memory, then I don't have a really good answer but throwing dirty data away > >seems like a bad answer to me. > > The problem is that we cannot unmount the corrupted filesystem due to > un-killable dd process. We must bring down the system to resume the service > with no dirty pages. I think it is important for the service continuity > to be able to kill the thread handling in balance_dirty_pages(). Sure. Then allowing a process to be killed while waiting in balance_dirty_pages() would solve your problem. That can be done relatively easily. I can write the patch, just now the code is under rewrite from IO-less dirty throttling patches so I'll wait for a while for it to settle down. Honza -- Jan Kara SUSE Labs, CR