From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from aserp1040.oracle.com ([141.146.126.69]:25825 "EHLO aserp1040.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753469Ab3HEOSk (ORCPT ); Mon, 5 Aug 2013 10:18:40 -0400 Date: Mon, 5 Aug 2013 22:18:18 +0800 From: Liu Bo To: Jan Schmidt Cc: linux-btrfs@vger.kernel.org Subject: Re: [RFC PATCH v5 4/5] Btrfs: disable qgroups accounting when quota is off Message-ID: <20130805141817.GB10401@localhost.localdomain> Reply-To: bo.li.liu@oracle.com References: <1375285066-14173-1-git-send-email-bo.li.liu@oracle.com> <1375285066-14173-5-git-send-email-bo.li.liu@oracle.com> <51FF9BD6.7000003@jan-o-sch.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii In-Reply-To: <51FF9BD6.7000003@jan-o-sch.net> Sender: linux-btrfs-owner@vger.kernel.org List-ID: On Mon, Aug 05, 2013 at 02:34:30PM +0200, Jan Schmidt wrote: > Nice try hiding this one in a dedup patch set, but I finally found it :-) Ahhhh, I didn't mean to ;-) > > On Wed, July 31, 2013 at 17:37 (+0200), Liu Bo wrote: > > So we don't need to do qgroups accounting trick without enabling quota. > > This reduces my tester's costing time from ~28s to ~23s. > > > > Signed-off-by: Liu Bo > > --- > > fs/btrfs/extent-tree.c | 6 ++++++ > > fs/btrfs/qgroup.c | 6 ++++++ > > 2 files changed, 12 insertions(+), 0 deletions(-) > > > > diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c > > index 10a5c72..c6612f5 100644 > > --- a/fs/btrfs/extent-tree.c > > +++ b/fs/btrfs/extent-tree.c > > @@ -2524,6 +2524,12 @@ int btrfs_delayed_refs_qgroup_accounting(struct btrfs_trans_handle *trans, > > struct qgroup_update *qgroup_update; > > int ret = 0; > > > > + if (!trans->root->fs_info->quota_enabled) { > > + if (trans->delayed_ref_elem.seq) > > + btrfs_put_tree_mod_seq(fs_info, &trans->delayed_ref_elem); > > + return 0; > > + } > > + > > if (list_empty(&trans->qgroup_ref_list) != > > !trans->delayed_ref_elem.seq) { > > /* list without seq or seq without list */ > > diff --git a/fs/btrfs/qgroup.c b/fs/btrfs/qgroup.c > > index 1280eff..f3e82aa 100644 > > --- a/fs/btrfs/qgroup.c > > +++ b/fs/btrfs/qgroup.c > > @@ -1200,6 +1200,9 @@ int btrfs_qgroup_record_ref(struct btrfs_trans_handle *trans, > > { > > struct qgroup_update *u; > > > > + if (!trans->root->fs_info->quota_enabled) > > + return 0; > > + > > BUG_ON(!trans->delayed_ref_elem.seq); > > u = kmalloc(sizeof(*u), GFP_NOFS); > > if (!u) > > @@ -1850,6 +1853,9 @@ out: > > > > void assert_qgroups_uptodate(struct btrfs_trans_handle *trans) > > { > > + if (!trans->root->fs_info->quota_enabled) > > + return; > > + > > if (list_empty(&trans->qgroup_ref_list) && !trans->delayed_ref_elem.seq) > > return; > > pr_err("btrfs: qgroups not uptodate in trans handle %p: list is%s empty, seq is %#x.%x\n", > > > > The second hunk looks sensible at first sight. However, hunk 1 and 3 don't. They > assert consistency of qgroup state in well defined places. The fact that you > need to disable those checks shows that skipping addition to the list in the > second hunk cannot be right, or at least not sufficient. I agree, only hunk 2 is necessary. > > We've got the list of qgroup operations trans->qgroup_ref_list and we've got the > qgroup's delayed ref blocker, trans->delayed_ref_elem. If you stop adding to the > list (hunk 2) which seems reasonable when quota is disabled, then you also must > ensure you're not acquiring the delayed ref blocker element, which should give > another performance boost. WHY a 'must' here? > > need_ref_seq may be the right place for this change. It just feels a bit too > obvious. The critical cases obviously are quota enable and quota disable. I just > don't recall why it wasn't that way from the very beginning of qgroups, I might > be missing something fundamental here. Yeah I thought about 'need_ref_seq', but the point is that delayed ref blocker not only serves qgroups accounting, but also features based on backref walking, such as scrub, snapshot-aware defragment. And I want dedup to work with all these features well, including qgroups too. Any ideas? -liubo