fs: dcache scale dentry refcount

Make d_count non-atomic and protect it with d_lock. This allows us to ensure a
0 refcount dentry remains 0 without dcache_lock. It is also fairly natural when
we start protecting many other dentry members with d_lock.

Signed-off-by: Nick Piggin <npiggin@kernel.dk>

3 files changed, 6 insertions, 4 deletions

diff --git a/fs/ceph/dir.c b/fs/ceph/dir.c
index d902948a90d8..3ecf915a4550 100644
--- a/fs/ceph/dir.c
+++ b/fs/ceph/dir.c
@@ -150,7 +150,9 @@ more:
                 di = ceph_dentry(dentry);
         }
 
-        atomic_inc(&dentry->d_count);
+        spin_lock(&dentry->d_lock);
+        dentry->d_count++;
+        spin_unlock(&dentry->d_lock);
         spin_unlock(&dcache_lock);
 
         dout(" %llu (%llu) dentry %p %.*s %p\n", di->offset, filp->f_pos,
diff --git a/fs/ceph/inode.c b/fs/ceph/inode.c
index bf1286588f26..bb68c799074d 100644
--- a/fs/ceph/inode.c
+++ b/fs/ceph/inode.c
@@ -879,8 +879,8 @@ static struct dentry *splice_dentry(struct dentry *dn, struct inode *in,
         } else if (realdn) {
                 dout("dn %p (%d) spliced with %p (%d) "
                      "inode %p ino %llx.%llx\n",
-                     dn, atomic_read(&dn->d_count),
-                     realdn, atomic_read(&realdn->d_count),
+                     dn, dn->d_count,
+                     realdn, realdn->d_count,
                      realdn->d_inode, ceph_vinop(realdn->d_inode));
                 dput(dn);
                 dn = realdn;
diff --git a/fs/ceph/mds_client.c b/fs/ceph/mds_client.c
index 38800eaa81d0..a50fca1e03be 100644
--- a/fs/ceph/mds_client.c
+++ b/fs/ceph/mds_client.c
@@ -1486,7 +1486,7 @@ retry:
         *base = ceph_ino(temp->d_inode);
         *plen = len;
         dout("build_path on %p %d built %llx '%.*s'\n",
-             dentry, atomic_read(&dentry->d_count), *base, len, path);
+             dentry, dentry->d_count, *base, len, path);
         return path;
 }