From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mx0b-00082601.pphosted.com ([67.231.153.30]:57307 "EHLO mx0b-00082601.pphosted.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752798AbaGWNZ4 (ORCPT ); Wed, 23 Jul 2014 09:25:56 -0400 Message-ID: <53CFB7D6.1040203@fb.com> Date: Wed, 23 Jul 2014 09:25:42 -0400 From: Josef Bacik MIME-Version: 1.0 To: , Mark Fasheh , Zach Brown , Dave Chinner , , , Chris Mason Subject: Re: [PATCH] xfstests/btrfs: add test for quota groups and drop snapshot References: <20140709224150.GA5484@wotan.suse.de> <20140710004330.GG4453@dastard> <20140710173614.GB5484@wotan.suse.de> <20140710183228.GD17201@lenny.home.zabbo.net> <20140710190055.GC5484@wotan.suse.de> <20140722190532.GI1553@twin.jikos.cz> <20140723123056.GL1553@twin.jikos.cz> In-Reply-To: <20140723123056.GL1553@twin.jikos.cz> Content-Type: text/plain; charset="ISO-8859-1"; format=flowed Sender: linux-btrfs-owner@vger.kernel.org List-ID: On 07/23/2014 08:30 AM, David Sterba wrote: > On Tue, Jul 22, 2014 at 09:05:32PM +0200, David Sterba wrote: >> On Thu, Jul 10, 2014 at 12:00:55PM -0700, Mark Fasheh wrote: >>> On Thu, Jul 10, 2014 at 11:32:28AM -0700, Zach Brown wrote: >>>> What interfaces would be needed for this to work precisely so we don't >>>> have to play this game ever again? >>> >>> Well there's also the 'sleep 45' below because we need to be certain that >>> btrfs_drop_snapshot gets run. This was all a bit of a pain during debugging >>> to be honest. >>> >>> So in my experience, an interface to make debugging easier would involve >>> running every delayed action in the file system to completion, including a >>> sync of dirty blocks to disk. In theory, this would include any delayed >>> actions that were kicked off as a result of the actions you are syncing. >>> You'd do it all from a point in time of course so that we don't spin forever >>> on a busy filesystem. I do not know whether this is feasible. >>> >>> Given something like that, you'd just replace the calls to sleep with 'btrfs >>> fi synctheworldandwait' and know that on return, the actions you just queued >>> up completed. >> >> Waiting until some subvolume gets completely removed needs some work. In >> your case the cleaner thread sleeps and is woken up at the transaction >> commit time. As there is no other activity on the filesystem this >> happens at the periodic commit time, usually 30 seconds. 'sync' will not >> help, because it needs a transaction in progress. >> >> I have patchset in works that addresses a different problem but >> introduces a functionality that keeps track of some global pending >> actions. This could be easily enhanced to trigger the commit with sync >> if there was a snapshot deletion since last commit regardless of a >> transaction running status. >> >> This still does not cover the part where we want a command that waits >> until a given subvolume is completely removed, but I have a draft for >> that as well. >> >> Unfortunatelly until both parts are in place the sleep is the only >> reliable way. Oh well. > > And it turned out to be much simpler, I was wrong about transaction > commit poking the cleaner thread. It's actually the transaction commit > thread that wakes up cleaner and that's why it's always at the periodic > commit time. > > The proposed fix is to wake up transaction thread from the sync ioctl > (not the generic sync call through). > > For the qgroup test needs it's enough to delete subvolumes, issue 'btrfs > fi sync' and wait until there are no subvols listed (btrfs list -d). > > Without the fix, this will take up to 30 seconds, with the fix it's > immediate. The test script will not need any change. > I'll just add a sync flag to the snapshot creation and then Mark can redo this test to use the sync flag once that stuff is in. Thanks, Josef