Sue LoVerso of the WiredTiger team wrote an article in two parts about updating the lock-free algorithm the WiredTiger write-ahead log uses to consolidate writes. The original algorithm, based on the research paper "Scalability of write-ahead logging on multicore and multisocket hardware" published in the Very Large Databases Journal, was a very nice peice of engineering, but was inappropriate for the loads WT would see as a storage engine embedded in MongoDB. To handle a large increase in the number of threads per available core, it had to be updated to be entirely wait-free.
Part 1: https://engineering.mongodb.com/post/breaking-the-wiredtiger-logjam-the-write-ahead-log-1-2
Part 2: https://engineering.mongodb.com/post/breaking-the-wiredtiger-logjam-the-wait-free-solution-2-2