We've had some issues with writeback in presence of memory reclaim at Facebook, and this patch set attempts to fix it up. The real functional change is the last patch in the series, the first 5 are prep and cleanup patches. The basic idea is that we have callers that call wakeup_flusher_threads() with nr_pages == 0. This means 'writeback everything'. For memory reclaim situations, we can end up queuing a TON of these kinds of writeback units. This can cause softlockups and further memory issues, since we allocate huge amounts of struct wb_writeback_work to handle this writeback. Handle this situation more gracefully. -- Jens Axboe
