Hello,
On Thu 13-08-15 18:44:15, Tejun Heo wrote:
> e79729123f63 ("writeback: don't issue wb_writeback_work if clean")
> updated writeback path to avoid kicking writeback work items if there
> are no inodes to be written out; unfortunately, the avoidance logic
> was too aggressive and made sync_inodes_sb() skip I_DIRTY_TIME inodes.
> This patch fixes the breakage by
>
> * Removing bdi_has_dirty_io() shortcut from bdi_split_work_to_wbs().
> The callers are already testing the condition.
>
> * Removing bdi_has_dirty_io() shortcut from sync_inodes_sb() so that
> it always calls into bdi_split_work_to_wbs().
>
> * Making bdi_split_work_to_wbs() consider the b_dirty_time list for
> WB_SYNC_ALL writebacks.
>
> Signed-off-by: Tejun Heo <tj@xxxxxxxxxx>
> Fixes: e79729123f63 ("writeback: don't issue wb_writeback_work if clean")
> Cc: Ted Ts'o <tytso@xxxxxxxxxx>
> Cc: Jan Kara <jack@xxxxxxxx>
So the patch looks good to me. But the fact that is fixes Eryu's problem
means there is something fishy going on. Either inodes get wrongly attached
to b_dirty_time list or bdi_has_dirty_io() somehow misbehaves only
temporarily and we don't catch it with the debug patch.
Can we add a test to wb_has_dirty_io() to also check whether it matches
bdi_has_dirty_io()? Since Eryu doesn't use lazytime (I assume, Eryu, please
speak up if you do), we could also warn if b_dirty_time lists get
non-empty. Hmm?
Honza
> ---
> Hello,
>
> So, this fixes I_DIRTY_TIME syncing problem for ext4 but AFAICS xfs
> doesn't even use the generic inode metadata writeback path, so this
> most likely won't do anything for the originally reported problem.
> I'll post another patch for debugging.
>
> Thanks.
>
> fs/fs-writeback.c | 18 +++++++++---------
> 1 file changed, 9 insertions(+), 9 deletions(-)
>
> --- a/fs/fs-writeback.c
> +++ b/fs/fs-writeback.c
> @@ -844,14 +844,15 @@ static void bdi_split_work_to_wbs(struct
> struct wb_iter iter;
>
> might_sleep();
> -
> - if (!bdi_has_dirty_io(bdi))
> - return;
> restart:
> rcu_read_lock();
> bdi_for_each_wb(wb, bdi, &iter, next_blkcg_id) {
> - if (!wb_has_dirty_io(wb) ||
> - (skip_if_busy && writeback_in_progress(wb)))
> + /* SYNC_ALL writes out I_DIRTY_TIME too */
> + if (!wb_has_dirty_io(wb) &&
> + (base_work->sync_mode == WB_SYNC_NONE ||
> + list_empty(&wb->b_dirty_time)))
> + continue;
> + if (skip_if_busy && writeback_in_progress(wb))
> continue;
>
> base_work->nr_pages = wb_split_bdi_pages(wb, nr_pages);
> @@ -899,8 +900,7 @@ static void bdi_split_work_to_wbs(struct
> {
> might_sleep();
>
> - if (bdi_has_dirty_io(bdi) &&
> - (!skip_if_busy || !writeback_in_progress(&bdi->wb))) {
> + if (!skip_if_busy || !writeback_in_progress(&bdi->wb)) {
> base_work->auto_free = 0;
> base_work->single_wait = 0;
> base_work->single_done = 0;
> @@ -2275,8 +2275,8 @@ void sync_inodes_sb(struct super_block *
> };
> struct backing_dev_info *bdi = sb->s_bdi;
>
> - /* Nothing to do? */
> - if (!bdi_has_dirty_io(bdi) || bdi == &noop_backing_dev_info)
> + /* bdi_has_dirty() ignores I_DIRTY_TIME but we can't, always kick wbs */
> + if (bdi == &noop_backing_dev_info)
> return;
> WARN_ON(!rwsem_is_locked(&sb->s_umount));
>
>
--
Jan Kara <jack@xxxxxxxx>
SUSE Labs, CR
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