On Fri, 2022-02-18 at 10:47 +0800, xiubli@xxxxxxxxxx wrote: > From: Xiubo Li <xiubli@xxxxxxxxxx> > > 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. > > The 'invalidate' word is not precise here, acutally it will rebuild > the snapshot existing contexts or just build none-existing ones, > rename it to 'rebuild_snapcs'. > > URL: https://tracker.ceph.com/issues/44100 > Signed-off-by: Xiubo Li <xiubli@xxxxxxxxxx> > --- > > Changed in V2: > - Thanks Zheng's feedback and switched to Zheng's patch. > - Rename invalidate to rebuild_snapcs. > > > > 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 dbf34f212596..6d55b8ba79d8 100644 > --- a/fs/ceph/snap.c > +++ b/fs/ceph/snap.c > @@ -735,7 +735,8 @@ 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); > > @@ -743,6 +744,7 @@ 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); > @@ -766,7 +768,7 @@ 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", > @@ -791,22 +793,30 @@ 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 (rebuild_snapcs && p >= e) > + rebuild_snap_realms(realm_to_rebuild, &dirty_realms); > > if (!first_realm) > first_realm = realm; Looks good, Xiubo. Dropped the old patch and merged this one into the testing branch (with a little changelog cleanup). Thanks to both you and Zheng! -- Jeff Layton <jlayton@xxxxxxxxxx>
