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 5AF82BC9 for ; Thu, 9 Jul 2015 23:51:34 +0000 (UTC) Received: from v094114.home.net.pl (v094114.home.net.pl [79.96.170.134]) by smtp1.linuxfoundation.org (Postfix) with SMTP id B621D12C for ; Thu, 9 Jul 2015 23:51:33 +0000 (UTC) From: "Rafael J. Wysocki" To: Jan Kara Date: Fri, 10 Jul 2015 02:18:02 +0200 Message-ID: <5032030.PDNd4cQKi4@vostro.rjw.lan> In-Reply-To: <20150709112510.GD2900@quack.suse.cz> References: <119701572.LaCIUMEEyV@vostro.rjw.lan> <20150709112510.GD2900@quack.suse.cz> MIME-Version: 1.0 Content-Transfer-Encoding: 7Bit Content-Type: text/plain; charset="utf-8" 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 Thursday, July 09, 2015 01:25:10 PM Jan Kara wrote: > 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? Pretty much nowhere. It would be good to revive that patch if the functionality is reliable, though. Thanks, Rafael