From patchwork Wed Apr 27 13:59:38 2016 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Chris Mason X-Patchwork-Id: 8957781 Return-Path: X-Original-To: patchwork-linux-btrfs@patchwork.kernel.org Delivered-To: patchwork-parsemail@patchwork2.web.kernel.org Received: from mail.kernel.org (mail.kernel.org [198.145.29.136]) by patchwork2.web.kernel.org (Postfix) with ESMTP id 7B8DFBF29F for ; Wed, 27 Apr 2016 14:00:41 +0000 (UTC) Received: from mail.kernel.org (localhost [127.0.0.1]) by mail.kernel.org (Postfix) with ESMTP id 5A1D820114 for ; Wed, 27 Apr 2016 14:00:40 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id BFA5B20109 for ; Wed, 27 Apr 2016 14:00:36 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752755AbcD0OAW (ORCPT ); Wed, 27 Apr 2016 10:00:22 -0400 Received: from mx0a-00082601.pphosted.com ([67.231.145.42]:57898 "EHLO mx0a-00082601.pphosted.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752039AbcD0N7o (ORCPT ); Wed, 27 Apr 2016 09:59:44 -0400 Received: from pps.filterd (m0044008.ppops.net [127.0.0.1]) by mx0a-00082601.pphosted.com (8.16.0.11/8.16.0.11) with SMTP id u3RDuGtV024851 for ; Wed, 27 Apr 2016 06:59:43 -0700 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=fb.com; h=date : from : to : cc : subject : message-id : references : mime-version : content-type : in-reply-to; s=facebook; bh=zVzQod7D3kP5jHTwLogLC5ckcTVjZ5PutK1GOJXpd90=; b=poSzYe+NiyUNS13Hmhyui9W6eLEBfa14NhvjbU5RNrVYpYMx/etyBDpa89JbgdC3ytwc sLLZqlaJvrrWdKjl7v8a5+6PAXUVuQx0oPsodifJspA94bW3cc4owC++MzDJ2wUoh3ma Ky4mk2h3ejuXU0dUST6w1KKsc+Yq/y2Ah1E= Received: from mail.thefacebook.com ([199.201.64.23]) by mx0a-00082601.pphosted.com with ESMTP id 22jv69ha94-1 (version=TLSv1 cipher=AES128-SHA bits=128 verify=NOT) for ; Wed, 27 Apr 2016 06:59:43 -0700 Received: from localhost (192.168.52.123) by mail.thefacebook.com (192.168.16.23) with Microsoft SMTP Server (TLS) id 14.3.248.2; Wed, 27 Apr 2016 06:59:39 -0700 Date: Wed, 27 Apr 2016 09:59:38 -0400 From: Chris Mason To: Josef Bacik CC: , Subject: Re: [PATCH] Btrfs: track transid for delayed ref flushing Message-ID: <20160427135938.pczv7f4ulrvwehqp@floor.thefacebook.com> Mail-Followup-To: Chris Mason , Josef Bacik , linux-btrfs@vger.kernel.org, kernel-team@fb.com References: <1460410660-17430-1-git-send-email-jbacik@fb.com> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <1460410660-17430-1-git-send-email-jbacik@fb.com> User-Agent: Mutt/1.5.23.1 (2014-03-12) X-Originating-IP: [192.168.52.123] X-Proofpoint-Spam-Reason: safe X-FB-Internal: Safe X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10432:, , definitions=2016-04-27_07:, , signatures=0 Sender: linux-btrfs-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-btrfs@vger.kernel.org X-Spam-Status: No, score=-7.8 required=5.0 tests=BAYES_00,DKIM_SIGNED, RCVD_IN_DNSWL_HI,RP_MATCHES_RCVD,T_DKIM_INVALID,UNPARSEABLE_RELAY autolearn=ham version=3.3.1 X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on mail.kernel.org X-Virus-Scanned: ClamAV using ClamSMTP On Mon, Apr 11, 2016 at 05:37:40PM -0400, Josef Bacik wrote: > Using the offwakecputime bpf script I noticed most of our time was spent waiting > on the delayed ref throttling. This is what is supposed to happen, but > sometimes the transaction can commit and then we're waiting for throttling that > doesn't matter anymore. So change this stuff to be a little smarter by tracking > the transid we were in when we initiated the throttling. If the transaction we > get is different then we can just bail out. This resulted in a 50% speedup in > my fs_mark test, and reduced the amount of time spent throttling by 60 seconds > over the entire run (which is about 30 minutes). Thanks, > > Signed-off-by: Josef Bacik > --- > fs/btrfs/ctree.h | 2 +- > fs/btrfs/extent-tree.c | 15 ++++++++++++--- > fs/btrfs/inode.c | 1 + > fs/btrfs/transaction.c | 3 ++- > 4 files changed, 16 insertions(+), 5 deletions(-) > > diff --git a/fs/btrfs/ctree.h b/fs/btrfs/ctree.h > index 55a24c5..4222936 100644 > --- a/fs/btrfs/ctree.h > +++ b/fs/btrfs/ctree.h > @@ -3505,7 +3505,7 @@ void btrfs_put_block_group(struct btrfs_block_group_cache *cache); > int btrfs_run_delayed_refs(struct btrfs_trans_handle *trans, > struct btrfs_root *root, unsigned long count); > int btrfs_async_run_delayed_refs(struct btrfs_root *root, > - unsigned long count, int wait); > + unsigned long count, u64 transid, int wait); > int btrfs_lookup_data_extent(struct btrfs_root *root, u64 start, u64 len); > int btrfs_lookup_extent_info(struct btrfs_trans_handle *trans, > struct btrfs_root *root, u64 bytenr, > diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c > index 4b5a517..f23f426 100644 > --- a/fs/btrfs/extent-tree.c > +++ b/fs/btrfs/extent-tree.c > @@ -2839,6 +2839,7 @@ int btrfs_should_throttle_delayed_refs(struct btrfs_trans_handle *trans, > > struct async_delayed_refs { > struct btrfs_root *root; > + u64 transid; > int count; > int error; > int sync; > @@ -2854,9 +2855,16 @@ static void delayed_ref_async_start(struct btrfs_work *work) > > async = container_of(work, struct async_delayed_refs, work); > > - trans = btrfs_join_transaction(async->root); > + trans = btrfs_attach_transaction(async->root); > if (IS_ERR(trans)) { > - async->error = PTR_ERR(trans); > + if (PTR_ERR(trans) != -ENOENT) > + async->error = PTR_ERR(trans); > + goto done; > + } This ends up deadlocking because btrfs_attach_transaction waits in ways that join does not. The differences between these two are really subtle, and we manage to make this mistake every year or so. Subject: [PATCH] btrfs: fix deadlock in delayed_ref_async_start "Btrfs: track transid for delayed ref flushing" was deadlocking on btrfs_attach_transaction because its not safe to call from the async delayed ref start code. This commit brings back btrfs_join_transaction instead and checks for a blocked commit. Signed-off-by: Josef Bacik Signed-off-by: Chris Mason --- fs/btrfs/extent-tree.c | 20 +++++++++++--------- 1 file changed, 11 insertions(+), 9 deletions(-) diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c index 6ce5b6c..44da4ac 100644 --- a/fs/btrfs/extent-tree.c +++ b/fs/btrfs/extent-tree.c @@ -2845,16 +2845,13 @@ static void delayed_ref_async_start(struct btrfs_work *work) async = container_of(work, struct async_delayed_refs, work); - trans = btrfs_attach_transaction(async->root); - if (IS_ERR(trans)) { - if (PTR_ERR(trans) != -ENOENT) - async->error = PTR_ERR(trans); + /* if the commit is already started, we don't need to wait here */ + if (btrfs_transaction_blocked(async->root->fs_info)) goto done; - } - /* Don't bother flushing if we got into a different transaction */ - if (trans->transid != async->transid) { - btrfs_end_transaction(trans, async->root); + trans = btrfs_join_transaction(async->root); + if (IS_ERR(trans)) { + async->error = PTR_ERR(trans); goto done; } @@ -2863,10 +2860,15 @@ static void delayed_ref_async_start(struct btrfs_work *work) * wait on delayed refs */ trans->sync = true; + + /* Don't bother flushing if we got into a different transaction */ + if (trans->transid > async->transid) + goto end; + ret = btrfs_run_delayed_refs(trans, async->root, async->count); if (ret) async->error = ret; - +end: ret = btrfs_end_transaction(trans, async->root); if (ret && !async->error) async->error = ret;