From e6fb6da2e10682d477f2fdb749451d9fe5d168e8 Mon Sep 17 00:00:00 2001 From: Wu Fengguang Date: Thu, 22 Jul 2010 10:23:44 -0600 Subject: writeback: try more writeback as long as something was written writeback_inodes_wb()/__writeback_inodes_sb() are not aggressive in that they only populate possibly a subset of eligible inodes into b_io at entrance time. When the queued set of inodes are all synced, they just return, possibly with all queued inode pages written but still wbc.nr_to_write > 0. For kupdate and background writeback, there may be more eligible inodes sitting in b_dirty when the current set of b_io inodes are completed. So it is necessary to try another round of writeback as long as we made some progress in this round. When there are no more eligible inodes, no more inodes will be enqueued in queue_io(), hence nothing could/will be synced and we may safely bail. For example, imagine 100 inodes i0, i1, i2, ..., i90, i91, i99 At queue_io() time, i90-i99 happen to be expired and moved to s_io for IO. When finished successfully, if their total size is less than MAX_WRITEBACK_PAGES, nr_to_write will be > 0. Then wb_writeback() will quit the background work (w/o this patch) while it's still over background threshold. This will be a fairly normal/frequent case I guess. Now that we do tagged sync and update inode->dirtied_when after the sync, this change won't livelock sync(1). I actually tried to write 1 page per 1ms with this command write-and-fsync -n10000 -S 1000 -c 4096 /fs/test and do sync(1) at the same time. The sync completes quickly on ext4, xfs, btrfs. Acked-by: Jan Kara Signed-off-by: Wu Fengguang --- fs/fs-writeback.c | 16 ++++++++-------- 1 file changed, 8 insertions(+), 8 deletions(-) diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c index e4504299f4a5..271cf2150ba0 100644 --- a/fs/fs-writeback.c +++ b/fs/fs-writeback.c @@ -739,22 +739,22 @@ static long wb_writeback(struct bdi_writeback *wb, wrote += write_chunk - wbc.nr_to_write; /* - * If we consumed everything, see if we have more + * Did we write something? Try for more + * + * Dirty inodes are moved to b_io for writeback in batches. + * The completion of the current batch does not necessarily + * mean the overall work is done. So we keep looping as long + * as made some progress on cleaning pages or inodes. */ - if (wbc.nr_to_write <= 0) + if (wbc.nr_to_write < write_chunk) continue; if (wbc.inodes_written) continue; /* - * Didn't write everything and we don't have more IO, bail + * No more inodes for IO, bail */ if (!wbc.more_io) break; - /* - * Did we write something? Try for more - */ - if (wbc.nr_to_write < write_chunk) - continue; /* * Nothing written. Wait for some inode to * become available for writeback. Otherwise -- cgit v1.2.1