Hello! This patch series addresses lockups reported by users when systemd unit reading lots of files from a filesystem mounted with lazytime mount option exits. See patch 3 for more details about the reproducer. There are two main issues why switching many inodes between wbs: 1) Multiple workers will be spawned to do the switching but they all contend on the same wb->list_lock making all the parallelism pointless and just wasting time. 2) Sorting of wb->b_dirty list by dirtied_time_when is inherently slow. Patches 1-3 address these problems, patch 4 adds a tracepoint for better observability of inode writeback switching. Honza
