From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Yan, Zheng " Subject: Re: Disk space accounting and subvolume delete Date: Wed, 12 May 2010 13:02:07 +0800 Message-ID: References: <20100510182352.GA21154@untroubled.org> <20100511154518.GA11710@untroubled.org> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 To: linux-btrfs@vger.kernel.org Return-path: In-Reply-To: <20100511154518.GA11710@untroubled.org> List-ID: On Tue, May 11, 2010 at 11:45 PM, Bruce Guenter = wrote: > On Tue, May 11, 2010 at 08:10:38AM +0800, Yan, Zheng =A0wrote: >> This is because the snapshot deleting ioctl only removes the a link. > > Right, I understand that. =A0That part is not unexpected, as it works= just > like unlink would. =A0However... > >> The corresponding tree is dropped in the background by a kernel thre= ad. > > The surprise is that 'sync', in any form I was able to try, does not > wait until all or even most of the I/O is completed. =A0Apparently th= e > standards spec for sync(2) says it is not required to wait for I/O to > complete, but AFAIK all other Linux FS do wait (the man page for sync= (2) > implies as much, as does the info page for sync in glibc). > > The only way I've found so far to force this behavior is to unmount, = and > that's rather intrusive to other users of the FS. > >> We could probably add another ioctl that waits until the tree has be= en >> completely dropped. > > Since the expected behavior for sync is to wait until all pending I/O > has been completed, I would argue this should be the default action f= or > sync. =A0Am I misunderstanding something? > Dropping a tree can be lengthy. It's not good to let sync wait for hour= s. =46or most linux FS, 'sync' just force an transaction/journal commit. I= don't think they wait for large operations that can span multiple transaction= s to complete. Yan, Zheng -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" = in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html