From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:55709) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1fIDE4-0002qz-FI for qemu-devel@nongnu.org; Mon, 14 May 2018 09:09:17 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1fIDE0-0007hY-Dy for qemu-devel@nongnu.org; Mon, 14 May 2018 09:09:16 -0400 From: Alberto Garcia In-Reply-To: <1525791496-125188-9-git-send-email-anton.nefedov@virtuozzo.com> References: <1525791496-125188-1-git-send-email-anton.nefedov@virtuozzo.com> <1525791496-125188-9-git-send-email-anton.nefedov@virtuozzo.com> Date: Mon, 14 May 2018 15:09:08 +0200 Message-ID: MIME-Version: 1.0 Content-Type: text/plain Subject: Re: [Qemu-devel] [PATCH v9 8/9] qcow2: skip writing zero buffers to empty COW areas List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Anton Nefedov , qemu-devel@nongnu.org Cc: qemu-block@nongnu.org, kwolf@redhat.com, mreitz@redhat.com, eblake@redhat.com, den@virtuozzo.com On Tue 08 May 2018 04:58:15 PM CEST, Anton Nefedov wrote: > If COW areas of the newly allocated clusters are zeroes on the backing image, > efficient bdrv_write_zeroes(flags=BDRV_REQ_ALLOCATE) can be used on the whole > cluster instead of writing explicit zero buffers later in perform_cow(). > > iotest 060: > write to the discarded cluster does not trigger COW anymore. > Use a backing image instead. > > Signed-off-by: Anton Nefedov Reviewed-by: Alberto Garcia Berto