Collection level locking isn't in 2.4. Working on more granular locking for 2.6/2.8. May skip collection level entirely for something more granular. More details can be found in the collection level locking ticket https://jira.mongodb.org/browse/SERVER-1240
From an atomicity perspective, yes. From a performance perspective, no; other concurrent operations affecting anything else on the whole database wait on your write.
