I'm really wondering about only trying once before taking the write lock. Yes, using the lsbit is a cute hack, but are we using it for its cuteness rather than its effectiveness? Renames happen occasionally. If that causes all the current pathname translations to fall back to the write lock, that is fairly heavy. Worse, all of those translations will (unnecessarily) bump the write seqcount, triggering *other* translations to fail back to the write-lock path. One patch to fix this would be to have the fallback read algorithm take sl->lock but *not* touch sl->seqcount, so it wouldn't break concurrent readers. But another is to simply retry at least once (two attempts) on the non-exclusive path before falling back to the exclusive one, This means that the count lsbit is no longer enough space for a retry counter, but oh, well. (If you really want to use one word, perhaps a better heuristic as to how to retry would be to examine the *number* of writes to the seqlock during the read. If there was only one, there's a fair chance that another read will succeed. If there was more than one (i.e. the seqlock has incremented by 3 or more), then forcing the writers to stop is probably necessary.) -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
