From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:55609) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1YIGz6-0007hR-Lh for qemu-devel@nongnu.org; Mon, 02 Feb 2015 08:24:13 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1YIGz0-0004qH-DV for qemu-devel@nongnu.org; Mon, 02 Feb 2015 08:24:10 -0500 Received: from mx1.redhat.com ([209.132.183.28]:46347) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1YIGz0-0004q7-3h for qemu-devel@nongnu.org; Mon, 02 Feb 2015 08:24:06 -0500 Date: Mon, 2 Feb 2015 14:23:55 +0100 From: Kevin Wolf Message-ID: <20150202132355.GC9478@noname.redhat.com> References: <1422607337-25335-1-git-send-email-den@openvz.org> <1422607337-25335-8-git-send-email-den@openvz.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1422607337-25335-8-git-send-email-den@openvz.org> Subject: Re: [Qemu-devel] [PATCH 7/7] block/raw-posix: set max_write_zeroes to INT_MAX for regular files List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: "Denis V. Lunev" Cc: Fam Zheng , Peter Lieven , qemu-devel@nongnu.org, Stefan Hajnoczi Am 30.01.2015 um 09:42 hat Denis V. Lunev geschrieben: > fallocate() works fine and could handle properly with arbitrary size > requests. There is no sense to reduce the amount of space to fallocate. > The bigger is the size, the better is the performance as the amount of > journal updates is reduced. > > The patch changes behavior for both generic filesystem and XFS codepaths, > which are different in handle_aiocb_write_zeroes. The implementation > of fallocate and xfsctl(XFS_IOC_ZERO_RANGE) for XFS are exactly the same > thus the change is fine for both ways. > > Signed-off-by: Denis V. Lunev > Reviewed-by: Max Reitz > CC: Kevin Wolf > CC: Stefan Hajnoczi > CC: Peter Lieven > CC: Fam Zheng > --- > block/raw-posix.c | 17 +++++++++++++++++ > 1 file changed, 17 insertions(+) > > diff --git a/block/raw-posix.c b/block/raw-posix.c > index 7b42f37..933c778 100644 > --- a/block/raw-posix.c > +++ b/block/raw-posix.c > @@ -293,6 +293,20 @@ static void raw_probe_alignment(BlockDriverState *bs, int fd, Error **errp) > } > } > > +static void raw_probe_max_write_zeroes(BlockDriverState *bs) > +{ > + BDRVRawState *s = bs->opaque; > + struct stat st; > + > + if (fstat(s->fd, &st) < 0) { > + return; /* no problem, keep default value */ > + } > + if (!S_ISREG(st.st_mode) || !s->discard_zeroes) { > + return; > + } > + bs->bl.max_write_zeroes = INT_MAX; > +} Peter, do you remember why INT_MAX isn't actually the default? I think the most reasonable behaviour would be that a limitation is only used if a block driver requests it, and otherwise unlimited is assumed. We can take this patch to raw-posix, it is certainly not wrong. But any format driver or filter will still, in most cases needlessly, apply MAX_WRITE_ZEROES_DEFAULT, i.e. a 16 MB maximum, so I think we should consider making a change to the default. Kevin