From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from aserp1040.oracle.com ([141.146.126.69]:31062 "EHLO aserp1040.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753541AbdHUTRb (ORCPT ); Mon, 21 Aug 2017 15:17:31 -0400 Date: Mon, 21 Aug 2017 12:14:16 -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: <20170821191416.GB26279@lim.localdomain> Reply-To: bo.li.liu@oracle.com References: <20170818174207.21613-1-bo.li.liu@oracle.com> <20170821174800.GF23807@destiny> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii In-Reply-To: <20170821174800.GF23807@destiny> Sender: linux-btrfs-owner@vger.kernel.org List-ID: 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. thanks, -liubo