ceph: avoid sending unnessesary FLUSHSNAP message

when a snap notification contains no new snapshot, we can avoid
sending FLUSHSNAP message to MDS. But we still need to create
cap_snap in some case because it's required by write path and
page writeback path

Signed-off-by: Yan, Zheng <zyan@redhat.com>

1 files changed, 38 insertions, 31 deletions

diff --git a/fs/ceph/caps.c b/fs/ceph/caps.c
index feb8ec92f1b4..f1dbcae7c75c 100644
--- a/fs/ceph/caps.c
+++ b/fs/ceph/caps.c
@@ -1297,11 +1297,8 @@ retry:
                 if (capsnap->dirty_pages || capsnap->writing)
                         break;
 
-                /*
-                 * if cap writeback already occurred, we should have dropped
-                 * the capsnap in ceph_put_wrbuffer_cap_refs.
-                 */
-                BUG_ON(capsnap->dirty == 0);
+                /* should be removed by ceph_try_drop_cap_snap() */
+                BUG_ON(!capsnap->need_flush);
 
                 /* pick mds, take s_mutex */
                 if (ci->i_auth_cap == NULL) {
@@ -2347,6 +2344,27 @@ void ceph_get_cap_refs(struct ceph_inode_info *ci, int caps)
         spin_unlock(&ci->i_ceph_lock);
 }
 
+
+/*
+ * drop cap_snap that is not associated with any snapshot.
+ * we don't need to send FLUSHSNAP message for it.
+ */
+static int ceph_try_drop_cap_snap(struct ceph_cap_snap *capsnap)
+{
+        if (!capsnap->need_flush &&
+            !capsnap->writing && !capsnap->dirty_pages) {
+
+                dout("dropping cap_snap %p follows %llu\n",
+                     capsnap, capsnap->follows);
+                ceph_put_snap_context(capsnap->context);
+                list_del(&capsnap->ci_item);
+                list_del(&capsnap->flushing_item);
+                ceph_put_cap_snap(capsnap);
+                return 1;
+        }
+        return 0;
+}
+
 /*
  * Release cap refs.
  *
@@ -2360,7 +2378,6 @@ void ceph_put_cap_refs(struct ceph_inode_info *ci, int had)
 {
         struct inode *inode = &ci->vfs_inode;
         int last = 0, put = 0, flushsnaps = 0, wake = 0;
-        struct ceph_cap_snap *capsnap;
 
         spin_lock(&ci->i_ceph_lock);
         if (had & CEPH_CAP_PIN)
@@ -2382,17 +2399,17 @@ void ceph_put_cap_refs(struct ceph_inode_info *ci, int had)
         if (had & CEPH_CAP_FILE_WR)
                 if (--ci->i_wr_ref == 0) {
                         last++;
-                        if (!list_empty(&ci->i_cap_snaps)) {
-                                capsnap = list_first_entry(&ci->i_cap_snaps,
-                                                     struct ceph_cap_snap,
-                                                     ci_item);
-                                if (capsnap->writing) {
-                                        capsnap->writing = 0;
-                                        flushsnaps =
-                                                __ceph_finish_cap_snap(ci,
-                                                                       capsnap);
-                                        wake = 1;
-                                }
+                        if (__ceph_have_pending_cap_snap(ci)) {
+                                struct ceph_cap_snap *capsnap =
+                                        list_last_entry(&ci->i_cap_snaps,
+                                                        struct ceph_cap_snap,
+                                                        ci_item);
+                                capsnap->writing = 0;
+                                if (ceph_try_drop_cap_snap(capsnap))
+                                        put++;
+                                else if (__ceph_finish_cap_snap(ci, capsnap))
+                                        flushsnaps = 1;
+                                wake = 1;
                         }
                         if (ci->i_wrbuffer_ref_head == 0 &&
                             ci->i_dirty_caps == 0 &&
@@ -2416,7 +2433,7 @@ void ceph_put_cap_refs(struct ceph_inode_info *ci, int had)
                 ceph_flush_snaps(ci);
         if (wake)
                 wake_up_all(&ci->i_cap_wq);
-        if (put)
+        while (put-- > 0)
                 iput(inode);
 }
 
@@ -2467,25 +2484,15 @@ void ceph_put_wrbuffer_cap_refs(struct ceph_inode_info *ci, int nr,
                 capsnap->dirty_pages -= nr;
                 if (capsnap->dirty_pages == 0) {
                         complete_capsnap = 1;
-                        if (capsnap->dirty == 0)
-                                /* cap writeback completed before we created
-                                 * the cap_snap; no FLUSHSNAP is needed */
-                                drop_capsnap = 1;
+                        drop_capsnap = ceph_try_drop_cap_snap(capsnap);
                 }
                 dout("put_wrbuffer_cap_refs on %p cap_snap %p "
-                     " snap %lld %d/%d -> %d/%d %s%s%s\n",
+                     " snap %lld %d/%d -> %d/%d %s%s\n",
                      inode, capsnap, capsnap->context->seq,
                      ci->i_wrbuffer_ref+nr, capsnap->dirty_pages + nr,
                      ci->i_wrbuffer_ref, capsnap->dirty_pages,
                      last ? " (wrbuffer last)" : "",
-                     complete_capsnap ? " (complete capsnap)" : "",
-                     drop_capsnap ? " (drop capsnap)" : "");
-                if (drop_capsnap) {
-                        ceph_put_snap_context(capsnap->context);
-                        list_del(&capsnap->ci_item);
-                        list_del(&capsnap->flushing_item);
-                        ceph_put_cap_snap(capsnap);
-                }
+                     complete_capsnap ? " (complete capsnap)" : "");
         }
 
         spin_unlock(&ci->i_ceph_lock);