[{_id:"1","subArr":[{"input1":"a","subKey":1,"title":"s1"},{"input1":"b","subKey":2,"title":"s2"}]},{_id:"2","subArr":[{"input1":"a","subKey":1,"title":"s1"},]}]

db.collection.update({"subArr.title":{$eq:"s1"}},{$push:{"subArr":{"input1":"c","title":"s3"}}},/** For update multiple documents*/{multi:true})