On Thu, May 12, 2011 at 09:57:19PM +0800, Wu Fengguang wrote:
> When wbc.more_io was first introduced, it indicates whether there are
> at least one superblock whose s_more_io contains more IO work. Now with
> the per-bdi writeback, it can be replaced with a simple b_more_io test.
>
> Acked-by: Jan Kara <jack@xxxxxxx>
> Acked-by: Mel Gorman <mel@xxxxxxxxx>
> CC: Minchan Kim <minchan.kim@xxxxxxxxx>
> Signed-off-by: Wu Fengguang <fengguang.wu@xxxxxxxxx>
> ---
> fs/fs-writeback.c | 9 ++-------
> include/linux/writeback.h | 1 -
> include/trace/events/ext4.h | 6 ++----
> include/trace/events/writeback.h | 5 +----
> 4 files changed, 5 insertions(+), 16 deletions(-)
>
> --- linux-next.orig/fs/fs-writeback.c 2011-05-05 23:30:30.000000000 +0800
> +++ linux-next/fs/fs-writeback.c 2011-05-05 23:30:33.000000000 +0800
> @@ -560,12 +560,8 @@ static int writeback_sb_inodes(struct su
> iput(inode);
> cond_resched();
> spin_lock(&wb->list_lock);
> - if (wbc->nr_to_write <= 0) {
> - wbc->more_io = 1;
> + if (wbc->nr_to_write <= 0)
> return 1;
> - }
> - if (!list_empty(&wb->b_more_io))
> - wbc->more_io = 1;
> }
> /* b_io is empty */
> return 1;
> @@ -707,7 +703,6 @@ static long wb_writeback(struct bdi_writ
> wbc.older_than_this = &oldest_jif;
> }
>
> - wbc.more_io = 0;
> wbc.nr_to_write = write_chunk;
> wbc.pages_skipped = 0;
> wbc.inodes_cleaned = 0;
> @@ -755,7 +750,7 @@ retry:
> /*
> * No more inodes for IO, bail
> */
> - if (!wbc.more_io)
> + if (list_empty(&wb->b_more_io))
> break;
We're not holding the wb->list_lock here, so we need to be careful
here. I think this is safe given that there shuold only be one
flusher thread operating on the list, but when we expand to multiple
flusher threads per-bdi, this coul dbe a nasty landmine. A comment
is probably in order explaining why this is safe to check unlocked
right now...
Cheers,
Dave.
--
Dave Chinner
david@xxxxxxxxxxxxx
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