On Wed, Oct 07, 2009 at 03:38:49PM +0800, Wu Fengguang wrote: > A background flush work may run for ever. So it's reasonable for it to > mimic the kupdate behavior of syncing old/expired inodes first. I've looked at this a bit again after you pointed to this thread in the direct reclaim thread, and I think we should be even more aggressive in pushing out old inodes. We basically have two types of I/O done from wb_do_writeback: - either we want to write all inodes for a given bdi/superblock. That includes all WB_SYNC_ALL callers, but also things like writeback_inodes_sb and the wakeup_flusher_threads call from sys_sync. - or we have a specific goal, like for the background writeback or the wakeup_flusher_threads from free_more_memory. For the first case there's obviously no point in doing any older_than_this processing as we write out all inodes anyway. For the second case we should always do a older_than_this pass _first_. Rationale: we really should get the old inodes out ASAP, so that we keep the amount of changes lost on a crash in the boundaries. Furthermore the callers only need N pages cleaned, and they don't care where from. So if we can reach our goal with the older_than_this writeback we're fine. If the writeback loop is long enough we can keep doing more of these later on as well. Doing this should also help cleaning the code up a bit by moving the wb_check_old_data_flush logic into wb_writeback and getting rid of the for_kupdate paramter in struct wb_writeback_work. I'm not even sure it's worth keeping it in struct writeback_control. -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
