From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:45643) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1XKo5N-0004Io-6f for qemu-devel@nongnu.org; Fri, 22 Aug 2014 08:36:56 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1XKo5J-0003HJ-G7 for qemu-devel@nongnu.org; Fri, 22 Aug 2014 08:36:53 -0400 Received: from mx1.redhat.com ([209.132.183.28]:61398) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1XKo5J-0003HF-7g for qemu-devel@nongnu.org; Fri, 22 Aug 2014 08:36:49 -0400 Date: Fri, 22 Aug 2014 13:36:34 +0100 From: "Daniel P. Berrange" Message-ID: <20140822123634.GL8447@redhat.com> References: <20140728084846.GH31917@G08FNSTD100614.fnst.cn.fujitsu.com> <20140822122556.GJ14001@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20140822122556.GJ14001@redhat.com> Subject: Re: [Qemu-devel] [PATCH v12 0/6] qcow2, raw: add preallocation=full and preallocation=falloc Reply-To: "Daniel P. Berrange" List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: "Richard W.M. Jones" Cc: Kevin Wolf , Hu Tao , qemu-devel@nongnu.org, Max Reitz , Stefan Hajnoczi , Yasunori Goto On Fri, Aug 22, 2014 at 01:25:56PM +0100, Richard W.M. Jones wrote: > > On Mon, Jul 28, 2014 at 04:48:46PM +0800, Hu Tao wrote: > > ping... > > > > All the 6 patches have reviewed-by now. > > > > On Fri, Jul 11, 2014 at 02:09:57PM +0800, Hu Tao wrote: > > > This series adds two preallocation mode to qcow2 and raw: > > > > > > Option preallocation=full preallocates disk space for image by writing > > > zeros to disk, this ensures disk space in any cases. > > > > > > Option preallocation=falloc preallocates disk space by calling > > > posix_fallocate(). This is faster than preallocation=full. > > Sorry if this was discussed before, but why would anyone use > preallocation=full if preallocation=falloc was possible? > > Shouldn't preallocation=full simply use posix_fallocate if it's > available, and fall back to writing zeroes if not? posix_fallocate() will itself fallback to writing zeros to disk if the filesystem can't do the fast allocation method. So I can't see any reason to have separate options for this. Just have a preallocation=full option which - at compile time - chooses between posix_fallocate and write(). This is what we've done in libvirt for many years now and no one has ever asked for more http://libvirt.org/git/?p=libvirt.git;a=blob;f=src/util/virfile.c;h=b6f5e3f2cbbcc6768d764009b238b2349bee3fee;hb=HEAD#l1037 We actually try to use mmap() before going to write() since that is slightly faster. http://log.amitshah.net/2009/03/comparison-of-file-systems-and-speeding-up-applications/ Regards, Daniel -- |: http://berrange.com -o- http://www.flickr.com/photos/dberrange/ :| |: http://libvirt.org -o- http://virt-manager.org :| |: http://autobuild.org -o- http://search.cpan.org/~danberr/ :| |: http://entangle-photo.org -o- http://live.gnome.org/gtk-vnc :|