From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:42199) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1bpyfP-00062o-WD for qemu-devel@nongnu.org; Fri, 30 Sep 2016 10:20:01 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1bpyfN-0002z0-OE for qemu-devel@nongnu.org; Fri, 30 Sep 2016 10:19:58 -0400 Date: Fri, 30 Sep 2016 16:19:46 +0200 From: Kevin Wolf Message-ID: <20160930141946.GC12028@noname.redhat.com> References: <1474974892-5031-1-git-send-email-famz@redhat.com> <20160929124139.GB5916@stefanha-x1.localdomain> <20160930021205.GC29760@lemon> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20160930021205.GC29760@lemon> Subject: Re: [Qemu-devel] [Qemu-block] [PATCH v3] block: Turn on "unmap" in active commit List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Fam Zheng Cc: Stefan Hajnoczi , qemu-devel@nongnu.org, qemu-block@nongnu.org, Max Reitz Am 30.09.2016 um 04:12 hat Fam Zheng geschrieben: > On Thu, 09/29 13:41, Stefan Hajnoczi wrote: > > On Tue, Sep 27, 2016 at 07:14:52PM +0800, Fam Zheng wrote: > > > We already specified BDRV_O_UNMAP when opening images in 'qemu-img > > > commit', but didn't turn on the "unmap" in the active commit job. This > > > patch fixes that so that zeroed clusters in top image can be discarded > > > which is desired in the virt-sparsify use case, where a temporary > > > overlay is created and fstrim'ed before commiting back, to free space in > > > the original image. > > > > > > This also enables it for block-commit. > > > > > > Signed-off-by: Fam Zheng > > > --- > > > v3: Change the right parameter. > > > v2: Add "unmap" to block-commit as well. [Kevin] > > > --- > > > block/mirror.c | 2 +- > > > 1 file changed, 1 insertion(+), 1 deletion(-) > > > > > > diff --git a/block/mirror.c b/block/mirror.c > > > index f9d1fec..8847ec5 100644 > > > --- a/block/mirror.c > > > +++ b/block/mirror.c > > > @@ -1042,7 +1042,7 @@ void commit_active_start(const char *job_id, BlockDriverState *bs, > > > > > > mirror_start_job(job_id, bs, base, NULL, speed, 0, 0, > > > MIRROR_LEAVE_BACKING_CHAIN, > > > - on_error, on_error, false, cb, opaque, &local_err, > > > + on_error, on_error, true, cb, opaque, &local_err, > > > &commit_active_job_driver, false, base, auto_complete); > > > if (local_err) { > > > error_propagate(errp, local_err); > > > > Why is unmap an option at all? > > > > What's wrong with using BDRV_REQ_MAY_UNMAP on all > > blk_aio_pwrite_zeroes() calls? > > Because unmap is an QMP option of drive-backup. I think in the drive-mirror > context, it mitigates the limitation that we have no control over target's > BDRV_O_UNMAP (always inherited from source). Wouldn't the more straightforward implementation then be if qmp_drive_mirror() set BDRV_O_UNMAP for the target depending on the flag rather than passing the flag down to the mirror job? Hm... And should BDRV_O_UNMAP really be a BlockBackend option rather than a BDS one? We already enable it unconditionally on non-root nodes and it seems to make sense to me to allow discard e.g. from a block job, but not from the guest. Kevin