I'm too late to the thread, but wonder if locking might have to do with updating access times on the dirs on read--that would help justify a read-only workload taking some sort of exclusive lock. The "fix" there would be something like relatime to get atimes set infrequently.<p>There're def a ton of other possibilities. Some locking could be overbroad, like an exclusive lock where a reader lock would be enough. I don't see super-strong evidence that any locks involved are actually <i>global</i>, just that they're under contention here. And I can understand shipping a product with somewhat excessive locking because perf issues with specific workloads are a better problem to have with your shiny new FS rollout than data loss.<p>Anyway it's mostly shooting in the dark for us here (though cool some folks disassembled the functions), but there are some shots in the dark that look different from what I could find in the comments already here :)