ceph: don't invalidate page cache when inode is no longer used

ceph_check_caps() invalidate page cache when inode is not used
by any open file. This behaviour is not friendly for workload
that repeatly read files.
Signed-off-by: NYan, Zheng <zyan@redhat.com>

fs/ceph/caps.c

@@ -1655,9 +1655,8 @@ void ceph_check_caps(struct ceph_inode_info *ci, int flags,
 	    !S_ISDIR(inode->i_mode) &&		/* ignore readdir cache */
 	    ci->i_wrbuffer_ref == 0 &&		/* no dirty pages... */
 	    inode->i_data.nrpages &&		/* have cached pages */
-	    (file_wanted == 0 ||		/* no open files */
-	     (revoking & (CEPH_CAP_FILE_CACHE|
-			  CEPH_CAP_FILE_LAZYIO))) && /*  or revoking cache */
+	    (revoking & (CEPH_CAP_FILE_CACHE|
+			 CEPH_CAP_FILE_LAZYIO)) && /*  or revoking cache */
 	    !tried_invalidate) {
 		dout("check_caps trying to invalidate on %p\n", inode);
 		if (try_nonblocking_invalidate(inode) < 0) {

fs/ceph/mds_client.c

@@ -1430,6 +1430,13 @@ static int trim_caps_cb(struct inode *inode, struct ceph_cap *cap, void *arg)
 		if ((used | wanted) & CEPH_CAP_ANY_WR)
 			goto out;
 	}
+	/* The inode has cached pages, but it's no longer used.
+	 * we can safely drop it */
+	if (wanted == 0 && used == CEPH_CAP_FILE_CACHE &&
+	    !(oissued & CEPH_CAP_FILE_CACHE)) {
+	  used = 0;
+	  oissued = 0;
+	}
 	if ((used | wanted) & ~oissued & mine)
 		goto out;   /* we need these caps */
 
@@ -1438,7 +1445,7 @@ static int trim_caps_cb(struct inode *inode, struct ceph_cap *cap, void *arg)
 		/* we aren't the only cap.. just remove us */
 		__ceph_remove_cap(cap, true);
 	} else {
-		/* try to drop referring dentries */
+		/* try dropping referring dentries */
 		spin_unlock(&ci->i_ceph_lock);
 		d_prune_aliases(inode);
 		dout("trim_caps_cb %p cap %p  pruned, count now %d\n",