os/bluestore: insert new onode to the front position of onode LRU

When new added onode comes, it should go to the front of the LRU,
since it's least recently used.

Signed-off-by: Jianjian Huo <samuel.huo@gmail.com>

src/os/bluestore/BlueStore.cc

@@ -495,7 +495,7 @@ void BlueStore::OnodeHashLRU::add(const ghobject_t& oid, OnodeRef o)
   dout(30) << __func__ << " " << oid << " " << o << dendl;
   assert(onode_map.count(oid) == 0);
   onode_map[oid] = o;
-  lru.push_back(*o);
+  lru.push_front(*o);
 }
 
 BlueStore::OnodeRef BlueStore::OnodeHashLRU::lookup(const ghobject_t& oid)