From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 2DE7CC433EF for ; Sat, 19 Feb 2022 12:55:49 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S242247AbiBSM4G (ORCPT ); Sat, 19 Feb 2022 07:56:06 -0500 Received: from mxb-00190b01.gslb.pphosted.com ([23.128.96.19]:43806 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233494AbiBSM4E (ORCPT ); Sat, 19 Feb 2022 07:56:04 -0500 Received: from dfw.source.kernel.org (dfw.source.kernel.org [IPv6:2604:1380:4641:c500::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id DF8F11CB756 for ; Sat, 19 Feb 2022 04:55:45 -0800 (PST) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by dfw.source.kernel.org (Postfix) with ESMTPS id 57E1360AC9 for ; Sat, 19 Feb 2022 12:55:45 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 3BEEEC004E1; Sat, 19 Feb 2022 12:55:44 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1645275344; bh=4/VBZF6I6fLjxPiehz0zNSC3eoA1yZaGMvSxcURlgUI=; h=Subject:From:To:Cc:Date:In-Reply-To:References:From; b=JMTD9Nl4XrZNCGIdml8a45Lr4b3898YpkyCo2u6Dyeau8kz1uZz2AQNVDy4ld3NHL GnX0HB5Cdx1YHcU6QvckzbcC9qGqPY81Pq7rJVrzqOq7aTKmwf1j0+0EWwzzUkG3cd wlOmngFpRi9rY28PMmxJjBxO18OA16cId1nV5F+PPHGYigIC8/SBudzJLOgxQzmB4l B0wZHd6TkMIfqoZIZJ4voc+6uhmmYHDjboj5fBgJ2Q4fzWV4oLoZ8VuKYjwS0i930r zZZ0dXafrH6SVQ5tFz5g78bMGN1ujC6Ie8GtvwJHmBFsPIi/UoPAL49M5Ljve1C31S UeaamqI/5JtwA== Message-ID: Subject: Re: [PATCH v3] ceph: do not update snapshot context when there is no new snapshot From: Jeff Layton To: xiubli@redhat.com Cc: idryomov@gmail.com, vshankar@redhat.com, ceph-devel@vger.kernel.org Date: Sat, 19 Feb 2022 07:55:42 -0500 In-Reply-To: <20220219062833.30192-1-xiubli@redhat.com> References: <20220219062833.30192-1-xiubli@redhat.com> Content-Type: text/plain; charset="ISO-8859-15" User-Agent: Evolution 3.42.4 (3.42.4-1.fc35) MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: ceph-devel@vger.kernel.org On Sat, 2022-02-19 at 14:28 +0800, xiubli@redhat.com wrote: > From: Xiubo Li > > We will only track the uppest parent snapshot realm from which we > need to rebuild the snapshot contexts _downward_ in hierarchy. For > all the others having no new snapshot we will do nothing. > > This fix will avoid calling ceph_queue_cap_snap() on some inodes > inappropriately. For example, with the code in mainline, suppose there > are 2 directory hierarchies (with 6 directories total), like this: > > /dir_X1/dir_X2/dir_X3/ > /dir_Y1/dir_Y2/dir_Y3/ > > Firstly, make a snapshot under /dir_X1/dir_X2/.snap/snap_X2, then make a > root snapshot under /.snap/root_snap. Every time we make snapshots under > /dir_Y1/..., the kclient will always try to rebuild the snap context for > snap_X2 realm and finally will always try to queue cap snaps for dir_Y2 > and dir_Y3, which makes no sense. > > That's because the snap_X2's seq is 2 and root_snap's seq is 3. So when > creating a new snapshot under /dir_Y1/... the new seq will be 4, and > the mds will send the kclient a snapshot backtrace in _downward_ > order: seqs 4, 3. > > When ceph_update_snap_trace() is called, it will always rebuild the from > the last realm, that's the root_snap. So later when rebuilding the snap > context, the current logic will always cause it to rebuild the snap_X2 > realm and then try to queue cap snaps for all the inodes related in that > realm, even though it's not necessary. > > This is accompanied by a lot of these sorts of dout messages: > > "ceph: queue_cap_snap 00000000a42b796b nothing dirty|writing" > > Fix the logic to avoid this situation. > > Also, the 'invalidate' word is not precise here. In actuality, it will > cause a rebuild of the existing snapshot contexts or just build > non-existant ones. Rename it to 'rebuild_snapcs'. > > URL: https://tracker.ceph.com/issues/44100 > Signed-off-by: Xiubo Li > Signed-off-by: Jeff Layton > --- > > > > V3: > - Fixed the crash issue reproduced by Luís. > > > > > fs/ceph/snap.c | 28 +++++++++++++++++++--------- > 1 file changed, 19 insertions(+), 9 deletions(-) > > diff --git a/fs/ceph/snap.c b/fs/ceph/snap.c > index 32e246138793..25a29304b74d 100644 > --- a/fs/ceph/snap.c > +++ b/fs/ceph/snap.c > @@ -736,7 +736,8 @@ int ceph_update_snap_trace(struct ceph_mds_client *mdsc, > __le64 *prior_parent_snaps; /* encoded */ > struct ceph_snap_realm *realm = NULL; > struct ceph_snap_realm *first_realm = NULL; > - int invalidate = 0; > + struct ceph_snap_realm *realm_to_rebuild = NULL; > + int rebuild_snapcs; > int err = -ENOMEM; > LIST_HEAD(dirty_realms); > > @@ -744,6 +745,7 @@ int ceph_update_snap_trace(struct ceph_mds_client *mdsc, > > dout("update_snap_trace deletion=%d\n", deletion); > more: > + rebuild_snapcs = 0; > ceph_decode_need(&p, e, sizeof(*ri), bad); > ri = p; > p += sizeof(*ri); > @@ -767,7 +769,7 @@ int ceph_update_snap_trace(struct ceph_mds_client *mdsc, > err = adjust_snap_realm_parent(mdsc, realm, le64_to_cpu(ri->parent)); > if (err < 0) > goto fail; > - invalidate += err; > + rebuild_snapcs += err; > > if (le64_to_cpu(ri->seq) > realm->seq) { > dout("update_snap_trace updating %llx %p %lld -> %lld\n", > @@ -792,22 +794,30 @@ int ceph_update_snap_trace(struct ceph_mds_client *mdsc, > if (realm->seq > mdsc->last_snap_seq) > mdsc->last_snap_seq = realm->seq; > > - invalidate = 1; > + rebuild_snapcs = 1; > } else if (!realm->cached_context) { > dout("update_snap_trace %llx %p seq %lld new\n", > realm->ino, realm, realm->seq); > - invalidate = 1; > + rebuild_snapcs = 1; > } else { > dout("update_snap_trace %llx %p seq %lld unchanged\n", > realm->ino, realm, realm->seq); > } > > - dout("done with %llx %p, invalidated=%d, %p %p\n", realm->ino, > - realm, invalidate, p, e); > + dout("done with %llx %p, rebuild_snapcs=%d, %p %p\n", realm->ino, > + realm, rebuild_snapcs, p, e); > > - /* invalidate when we reach the _end_ (root) of the trace */ > - if (invalidate && p >= e) > - rebuild_snap_realms(realm, &dirty_realms); > + /* > + * this will always track the uppest parent realm from which > + * we need to rebuild the snapshot contexts _downward_ in > + * hierarchy. > + */ > + if (rebuild_snapcs) > + realm_to_rebuild = realm; > + > + /* rebuild_snapcs when we reach the _end_ (root) of the trace */ > + if (realm_to_rebuild && p >= e) > + rebuild_snap_realms(realm_to_rebuild, &dirty_realms); > > if (!first_realm) > first_realm = realm; Looks good, Xiubo. Dropped v2 and merged this one. Thanks, -- Jeff Layton