From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from aserp1040.oracle.com ([141.146.126.69]:18698 "EHLO aserp1040.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753665AbdHUT5X (ORCPT ); Mon, 21 Aug 2017 15:57:23 -0400 Date: Mon, 21 Aug 2017 12:54:06 -0700 From: Liu Bo To: Josef Bacik Cc: linux-btrfs@vger.kernel.org Subject: Re: [PATCH] Btrfs: make plug in writing meta blocks really work Message-ID: <20170821195405.GC26279@lim.localdomain> Reply-To: bo.li.liu@oracle.com References: <20170818174207.21613-1-bo.li.liu@oracle.com> <20170821174800.GF23807@destiny> <20170821191416.GB26279@lim.localdomain> <20170821192329.GG23807@destiny> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii In-Reply-To: <20170821192329.GG23807@destiny> Sender: linux-btrfs-owner@vger.kernel.org List-ID: On Mon, Aug 21, 2017 at 03:23:30PM -0400, Josef Bacik wrote: > On Mon, Aug 21, 2017 at 12:14:16PM -0700, Liu Bo wrote: > > On Mon, Aug 21, 2017 at 01:48:01PM -0400, Josef Bacik wrote: > > > On Fri, Aug 18, 2017 at 11:42:07AM -0600, Liu Bo wrote: > > > > We have started plug in btrfs_write_and_wait_marked_extents() but the > > > > generated IOs actually go to device's schedule IO list where the work > > > > is doing in another task, thus the started plug doesn't make any > > > > sense. > > > > > > > > And since we wait for IOs immediately after writing meta blocks, it's > > > > the same case as writing log tree, doing sync submit can merge more > > > > IOs. > > > > > > > > > > We're plugging when we do the per-device scheduled IO right? > > > > Yes, we are. > > > > > So we aren't > > > really gaining anything by it being async. Also we do a lot of work between the > > > time that we start writing the marked extents for the tree-log and when we > > > actually wait for them, so we really don't want to do a synchronous write out in > > > that case. > > > > Hmm, we've always been doing sync write for meta blocks of log > > tree/log root tree, because of EXTENT_BIO_TREE_LOG (introduced in > > commit de0022b9da616b95ea5b41eab32da825b0b5150f), and the commit log > > claimed about 15% performance gaining in O_SYNC workloads (maybe we > > need to re-evaluate it?). > > > > > Instead move the sync_writers into write_and_wait_marked_extents. > > > Thanks, > > > > I'm OK with the change, but if sync write benefits both transaction > > commit case and log tree case, we can unify them to %sync_writers > > instead of a bio_flag. > > > > Sigh you're right, I forgot about all of that. Just delete the magic bio flags > stuff and then this is fine. Thanks, > OK, good to know it, thanks for the comments. thanks, -liubo