On Thu 21-09-17 10:00:25, Jens Axboe wrote: > On 09/21/2017 09:36 AM, Jens Axboe wrote: > >> But more importantly once we are not guaranteed that we only have > >> a single global wb_writeback_work per bdi_writeback we should just > >> embedd that into struct bdi_writeback instead of dynamically > >> allocating it. > > > > We could do this as a followup. But right now the logic is that we > > can have on started (inflight), and still have one new queued. > > Something like the below would fit on top to do that. Gets rid of the > allocation and embeds the work item for global start-all in the > bdi_writeback structure. Hum, so when we consider stuff like embedded work item, I would somewhat prefer to handle this like we do for for_background and for_kupdate style writeback so that we don't have another special case. For these don't queue any item, we just queue writeback work into the workqueue (via wb_wakeup()). When flusher work gets processed wb_do_writeback() checks (after processing all normal writeback requests) whether conditions for these special writeback styles are met and if yes, it creates on-stack work item and processes it (see wb_check_old_data_flush() and wb_check_background_flush()). So in this case we would just set some flag in bdi_writeback when memory reclaim needs help and wb_do_writeback() would check for this flag and create and process writeback-all style writeback work. Granted this does not preserve ordering of requests (basically any specific request gets priority over writeback-whole-world request) but memory gets cleaned in either case so flusher should be doing what is needed. Honza -- Jan Kara <jack@xxxxxxxx> SUSE Labs, CR
