ceph: queue cap snap only when snap realm's context changes

If we create capsnap when snap realm's context does not change, the
new capsnap's snapc is equal to ci->i_head_snapc. Page writeback code
can't differentiates dirty pages associated with the new capsnap from
dirty pages associated with i_head_snapc.

Signed-off-by: "Yan, Zheng" <zyan@redhat.com>
Signed-off-by: Ilya Dryomov <idryomov@gmail.com>

1 files changed, 16 insertions, 21 deletions

diff --git a/fs/ceph/snap.c b/fs/ceph/snap.c
index dab5d6732345..1ffc8b426c1c 100644
--- a/fs/ceph/snap.c
+++ b/fs/ceph/snap.c
@@ -299,7 +299,8 @@ static int cmpu64_rev(const void *a, const void *b)
 /*
  * build the snap context for a given realm.
  */
-static int build_snap_context(struct ceph_snap_realm *realm)
+static int build_snap_context(struct ceph_snap_realm *realm,
+                              struct list_head* dirty_realms)
 {
         struct ceph_snap_realm *parent = realm->parent;
         struct ceph_snap_context *snapc;
@@ -313,7 +314,7 @@ static int build_snap_context(struct ceph_snap_realm *realm)
          */
         if (parent) {
                 if (!parent->cached_context) {
-                        err = build_snap_context(parent);
+                        err = build_snap_context(parent, dirty_realms);
                         if (err)
                                 goto fail;
                 }
@@ -332,7 +333,7 @@ static int build_snap_context(struct ceph_snap_realm *realm)
                      " (unchanged)\n",
                      realm->ino, realm, realm->cached_context,
                      realm->cached_context->seq,
-                     (unsigned int) realm->cached_context->num_snaps);
+                     (unsigned int)realm->cached_context->num_snaps);
                 return 0;
         }
 
@@ -373,7 +374,11 @@ static int build_snap_context(struct ceph_snap_realm *realm)
              realm->ino, realm, snapc, snapc->seq,
              (unsigned int) snapc->num_snaps);
 
-        ceph_put_snap_context(realm->cached_context);
+        if (realm->cached_context) {
+                ceph_put_snap_context(realm->cached_context);
+                /* queue realm for cap_snap creation */
+                list_add_tail(&realm->dirty_item, dirty_realms);
+        }
         realm->cached_context = snapc;
         return 0;
 
@@ -394,15 +399,16 @@ fail:
 /*
  * rebuild snap context for the given realm and all of its children.
  */
-static void rebuild_snap_realms(struct ceph_snap_realm *realm)
+static void rebuild_snap_realms(struct ceph_snap_realm *realm,
+                                struct list_head *dirty_realms)
 {
         struct ceph_snap_realm *child;
 
         dout("rebuild_snap_realms %llx %p\n", realm->ino, realm);
-        build_snap_context(realm);
+        build_snap_context(realm, dirty_realms);
 
         list_for_each_entry(child, &realm->children, child_item)
-                rebuild_snap_realms(child);
+                rebuild_snap_realms(child, dirty_realms);
 }
 
 
@@ -624,13 +630,11 @@ static void queue_realm_cap_snaps(struct ceph_snap_realm *realm)
 {
         struct ceph_inode_info *ci;
         struct inode *lastinode = NULL;
-        struct ceph_snap_realm *child;
 
         dout("queue_realm_cap_snaps %p %llx inodes\n", realm, realm->ino);
 
         spin_lock(&realm->inodes_with_caps_lock);
-        list_for_each_entry(ci, &realm->inodes_with_caps,
-                            i_snap_realm_item) {
+        list_for_each_entry(ci, &realm->inodes_with_caps, i_snap_realm_item) {
                 struct inode *inode = igrab(&ci->vfs_inode);
                 if (!inode)
                         continue;
@@ -643,14 +647,6 @@ static void queue_realm_cap_snaps(struct ceph_snap_realm *realm)
         spin_unlock(&realm->inodes_with_caps_lock);
         iput(lastinode);
 
-        list_for_each_entry(child, &realm->children, child_item) {
-                dout("queue_realm_cap_snaps %p %llx queue child %p %llx\n",
-                     realm, realm->ino, child, child->ino);
-                list_del_init(&child->dirty_item);
-                list_add(&child->dirty_item, &realm->dirty_item);
-        }
-
-        list_del_init(&realm->dirty_item);
         dout("queue_realm_cap_snaps %p %llx done\n", realm, realm->ino);
 }
 
@@ -721,8 +717,6 @@ more:
                 if (err < 0)
                         goto fail;
 
-                /* queue realm for cap_snap creation */
-                list_add(&realm->dirty_item, &dirty_realms);
                 if (realm->seq > mdsc->last_snap_seq)
                         mdsc->last_snap_seq = realm->seq;
 
@@ -741,7 +735,7 @@ more:
 
         /* invalidate when we reach the _end_ (root) of the trace */
         if (invalidate && p >= e)
-                rebuild_snap_realms(realm);
+                rebuild_snap_realms(realm, &dirty_realms);
 
         if (!first_realm)
                 first_realm = realm;
@@ -758,6 +752,7 @@ more:
         while (!list_empty(&dirty_realms)) {
                 realm = list_first_entry(&dirty_realms, struct ceph_snap_realm,
                                          dirty_item);
+                list_del_init(&realm->dirty_item);
                 queue_realm_cap_snaps(realm);
         }