Age-Memory Trade-off in Read-Copy-Update

In the realm of shared memory systems, the challenge of reader-writer synchronization is closely coupled with the potential for readers to access outdated updates. Read-Copy-Update (RCU) is a synchronization primitive that allows for concurrent and non-blocking read access to fresh data. This is achieved through the creation of updated data copies, with each prior version retained until all associated read-locks are released. Given the principle that frequent updating keeps information fresh, the concern is whether the accumulation of update copies leads to excessive memory usage. To address this, we analyze trade-offs between memory usage and update age within real-time status updating systems, focusing specifically on RCU. The analysis demonstrates that with finite read time and read request rate, the average number of updates within the system remains bounded.