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The current orphan scan uses the forest_next_hint to look for candidate orphan items to delete. It doesn't skip deleted items and checks the forest of log btrees so it'd return hints for every single item that existed in all the log btrees across the system. And we call the hint per-item. When the system is deleting a lot of files we end up generating a huge load where all mounts are constantly getting the btree roots from the server, reading all the newest log btree blocks, finding deleted orphan items for inodes that have already been deleted, and moving on to the next deleted orphan item. The fix is to use a read-only traversal of only one version of the fs root for all the items in one scan. This avoids all the deleted orphan items that exist in the log btrees which will disappear when they're merged. It lets the item iteration happen in a single read-only cached btree instead of constantly reading in the most recently written root block of every log btree. The result is an enormous speedup of large deletions. I don't want to describe exactly how enormous. Signed-off-by: Zach Brown <zab@versity.com>