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

Jan Kara
2010-07-29T15:02:41Z

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