From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from smtp1.linuxfoundation.org (smtp1.linux-foundation.org [172.17.192.35]) by mail.linuxfoundation.org (Postfix) with ESMTPS id 0DAD5B68 for ; Thu, 9 Jul 2015 11:43:44 +0000 (UTC) Received: from mx2.suse.de (cantor2.suse.de [195.135.220.15]) by smtp1.linuxfoundation.org (Postfix) with ESMTPS id 8ADC5108 for ; Thu, 9 Jul 2015 11:43:43 +0000 (UTC) Date: Thu, 9 Jul 2015 13:25:10 +0200 From: Jan Kara To: "Rafael J. Wysocki" Message-ID: <20150709112510.GD2900@quack.suse.cz> References: <9412727.0bKgPF9YKr@vostro.rjw.lan> <119701572.LaCIUMEEyV@vostro.rjw.lan> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <119701572.LaCIUMEEyV@vostro.rjw.lan> Cc: ksummit-discuss@lists.linuxfoundation.org Subject: Re: [Ksummit-discuss] [TECH TOPIC] giving freezer well-defined semantics List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , On Wed 08-07-15 23:55:09, Rafael J. Wysocki wrote: > On Wednesday, July 08, 2015 10:16:39 AM Jiri Kosina wrote: > > On Wed, 8 Jul 2015, Rafael J. Wysocki wrote: > > > > > OK, it is necessary to ensure that the contents of the image will be > > > consistent with the state of filesystems on the storage media, so > > > everything that may change that state should be "frozen" before the > > > image is created, but "frozen" in terms of "no persistent state changes > > > from now on" rather than in terms of "no forward progress from now on". > > > > Yeah. So again, why do we even have freezer for so many kernel threads at > > all? :) > > Well, one reason may be that we've never grown a decent mechanism for freezing > filesystems (as in "no persistent state changes from now on") and people try to > make up for that by stopping things if they can (but in the kernel space that's > inherently racy). The most common filesystems - xfs, ext4, ext3, btrfs - handle freezing fine these days. And the filesystem freezing is used by LVM snapshots, Virtualization guest snapshots etc. so it is even tested ;). I know you have proposed to use fs freezing during hibernation some time ago but I don't remember where it ended up... Do you remember? Honza -- Jan Kara SUSE Labs, CR