New code for 5.9: - Fix some btree block pingponging problems when swapping extents - Redesign the reflink copy loop so that we only run one remapping operation per transaction. This helps us avoid running out of block reservation on highly deduped filesystems. - Take the MMAPLOCK around filemap_map_pages. - Make inode reclaim fully async so that we avoid stalling processes on flushing inodes to disk. - Reduce inode cluster buffer RMW cycles by attaching the buffer to dirty inodes so we won't let go of the cluster buffer when we know we're going to need it soon. - Add some more checks to the realtime bitmap file scrubber. - Don't trip false lockdep warnings in fs freeze.