From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:53103) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1avJ1J-0000Nf-31 for qemu-devel@nongnu.org; Wed, 27 Apr 2016 02:32:22 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1avJ1A-0008Dz-Qy for qemu-devel@nongnu.org; Wed, 27 Apr 2016 02:32:17 -0400 Received: from mail-am1on0147.outbound.protection.outlook.com ([157.56.112.147]:52032 helo=emea01-am1-obe.outbound.protection.outlook.com) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1avJ1A-0008Dp-9M for qemu-devel@nongnu.org; Wed, 27 Apr 2016 02:32:12 -0400 References: <1461400913-7321-1-git-send-email-den@openvz.org> <20160426094654.GE10650@stefanha-x1.localdomain> From: "Denis V. Lunev" Message-ID: <57205CE2.4070009@openvz.org> Date: Wed, 27 Apr 2016 09:32:02 +0300 MIME-Version: 1.0 In-Reply-To: <20160426094654.GE10650@stefanha-x1.localdomain> Content-Type: text/plain; charset="windows-1252"; format=flowed Content-Transfer-Encoding: 7bit Subject: Re: [Qemu-devel] [PATCH for 2.7 0/2] backup compression List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Stefan Hajnoczi Cc: qemu-devel@nongnu.org, Pavel Butsykin , Jeff Cody , Markus Armbruster , John Snow , Kevin Wolf On 04/26/2016 12:46 PM, Stefan Hajnoczi wrote: > On Sat, Apr 23, 2016 at 11:41:51AM +0300, Denis V. Lunev wrote: >> The idea is simple - backup is "written-once" data. It is written block >> by block and it is large enough. It would be nice to save storage >> space and compress it. >> >> These patches add the ability to compress data during backup. This >> functionality is implemented by means of adding options to the qmp/hmp >> commands(drive-backup, blockdev-backup). The implementation is quite >> simple, because the responsibility for data compression imposed on the >> format driver. >> >> Signed-off-by: Pavel Butsykin >> Signed-off-by: Denis V. Lunev >> CC: Jeff Cody >> CC: Markus Armbruster >> CC: Eric Blake >> CC: John Snow >> >> Pavel Butsykin (2): >> drive-backup: added support for data compression >> blockdev-backup: added support for data compression >> >> block/backup.c | 13 +++++++++++++ >> blockdev.c | 20 ++++++++++++++++++-- >> hmp-commands.hx | 8 +++++--- >> hmp.c | 3 ++- >> include/block/block_int.h | 1 + >> qapi/block-core.json | 3 ++- >> qmp-commands.hx | 7 +++++-- >> 7 files changed, 46 insertions(+), 9 deletions(-) > bdrv_write_compressed() hasn't been called from a running VM before, it > was purely a synchronous qemu-img operation. The > qcow2.c:qcow2_write_compressed() code doesn't seem to be written with > coroutine context in mind but I think the lock in > block/backup.c:backup_do_cow() will protect against race conditions. > > Please include a test case (using qcow2?). I have looked into the code. The only problematic thing there is that the compression is performed directly in the write, which could take a bit of time. Thus responsiveness of the guest system could be reduced. Though I do not expect here troubles. I think that it is worth to give this tech a chance. Compression could be moved to the outer thread in the next step if required. Den