diff --git a/kernel/fileobj.c b/kernel/fileobj.c
index cc3c008e..79f38fb3 100644
--- a/kernel/fileobj.c
+++ b/kernel/fileobj.c
@@ -226,12 +226,26 @@ int fileobj_create(int fd, struct memobj **objp, int *maxprotp)
 		obj_list_insert(newobj);
 		obj = newobj;
 		to_memobj(obj)->flags |= result.flags;
+		to_memobj(obj)->status = MEMOBJ_READY;
+		if (to_memobj(obj)->flags & MF_PREFETCH) {
+			to_memobj(obj)->status = MEMOBJ_TO_BE_PREFETCHED;
+		}
 		newobj = NULL;
+		dkprintf("%s: new obj 0x%lx cref: %d, %s\n",
+			__FUNCTION__,
+			obj,
+			obj->cref,
+			to_memobj(obj)->flags & MF_ZEROFILL ? "zerofill" : "");
 	}
 	else {
 		++obj->sref;
 		++obj->cref;
 		memobj_unlock(&obj->memobj);	/* locked by obj_list_lookup() */
+		dkprintf("%s: existing obj 0x%lx cref: %d, %s\n",
+			__FUNCTION__,
+			obj,
+			obj->cref,
+			to_memobj(obj)->flags & MF_ZEROFILL ? "zerofill" : "");
 	}
 
 	mcs_rwlock_writer_unlock_noirq(&fileobj_list_lock, &node);
@@ -281,7 +295,13 @@ static void fileobj_release(struct memobj *memobj)
 	memobj_unlock(&obj->memobj);
 
 	if (free_obj) {
-		mcs_lock_lock_noirq(&fileobj_list_lock, &node);
+		dkprintf("%s: release obj 0x%lx cref: %d, free_obj: 0x%lx, %s\n",
+				__FUNCTION__,
+				obj,
+				obj->cref,
+				free_obj,
+				to_memobj(obj)->flags & MF_ZEROFILL ? "zerofill" : "");
+		mcs_rwlock_writer_lock_noirq(&fileobj_list_lock, &node);
 		/* zap page_list */
 		for (;;) {
 			struct page *page;
diff --git a/kernel/include/memobj.h b/kernel/include/memobj.h
index 79ac70fc..965fd9b4 100644
--- a/kernel/include/memobj.h
+++ b/kernel/include/memobj.h
@@ -37,11 +37,14 @@ enum {
 	MF_END
 };
 
+#define MEMOBJ_READY              0
+#define MEMOBJ_TO_BE_PREFETCHED   1
+
 struct memobj {
-	struct memobj_ops *	ops;
-	uint32_t		flags;
-	int8_t			padding[4];
-	ihk_spinlock_t		lock;
+	struct memobj_ops *ops;
+	uint32_t flags;
+	uint32_t status;
+	ihk_spinlock_t lock;
 };
 
 typedef void memobj_release_func_t(struct memobj *obj);
diff --git a/kernel/syscall.c b/kernel/syscall.c
index 63315f3b..64336386 100644
--- a/kernel/syscall.c
+++ b/kernel/syscall.c
@@ -1363,9 +1363,12 @@ do_mmap(const intptr_t addr0, const size_t len0, const int prot,
 		goto out;
 	}
 
-	if (memobj->flags & MF_PREFETCH) {
+	memobj_lock(memobj);
+	if (memobj->status == MEMOBJ_TO_BE_PREFETCHED) {
+		memobj->status = MEMOBJ_READY;
 		populated_mapping = 1;
 	}
+	memobj_unlock(memobj);
 
 	error = 0;
 	p = NULL;