Re: [PATCH 3/5] writeback: prevent sync livelock with the sync_after timestamp

[Jan Kara <jack@suse.cz>]

  Hi Fengguang,

On Thu 29-07-10 19:51:45, Wu Fengguang wrote:
> The start time in writeback_inodes_wb() is not very useful because it
> slips at each invocation time. Preferrably one _constant_ time shall be
> used at the beginning to cover the whole sync() work.
> 
> The newly dirtied inodes are now guarded at the queue_io() time instead
> of the b_io walk time. This is more natural: non-empty b_io/b_more_io
> means "more work pending".
> 
> The timestamp is now grabbed the sync work submission time, and may be
> further optimized to the initial sync() call time.
  The patch seems to have some issues...

> +	if (wbc->for_sync) {
  For example this is never set. You only set wb->for_sync.

> +		expire_interval = 1;
> +		older_than_this = wbc->sync_after;
  And sync_after is never set either???

> -	if (!(wbc->for_kupdate || wbc->for_background) || list_empty(&wb->b_io))
> +	if (list_empty(&wb->b_io))
>  		queue_io(wb, wbc);
  And what is the purpose of this? It looks as an unrelated change to me.

								Honza
-- 
Jan Kara <jack@suse.cz>
SUSE Labs, CR