Re: 2.6.23-rc6-mm1 -- mkfs stuck in 'D'

Peter Zijlstra
2007-09-20T12:15:46Z

On Thu, 20 Sep 2007 12:31:39 +0100 (BST) Hugh Dickins
<hugh@veritas.com> wrote:

Thanks Hugh!

> [PATCH mm] mm per-device dirty threshold fix
>
> Fix occasional hang when a task couldn't get out of balance_dirty_pages:
> mm-per-device-dirty-threshold.patch needs to reevaluate bdi_nr_writeback
> across all cpus when bdi_thresh is low, even in the case when there was
> no bdi_nr_reclaimable.
>
> Signed-off-by: Hugh Dickins <hugh@veritas.com>

Acked-by: Peter Zijlstra <a.p.zijlstra@chello.nl>

> ---
> mm/page-writeback.c | 53 +++++++++++++++++++-----------------------
> 1 file changed, 24 insertions(+), 29 deletions(-)
>
> --- 2.6.23-rc6-mm1/mm/page-writeback.c 2007-09-18 12:28:25.000000000 +0100
> +++ linux/mm/page-writeback.c 2007-09-19 20:00:46.000000000 +0100
> @@ -379,7 +379,7 @@ static void balance_dirty_pages(struct a
> bdi_nr_reclaimable = bdi_stat(bdi, BDI_RECLAIMABLE);
> bdi_nr_writeback = bdi_stat(bdi, BDI_WRITEBACK);
> if (bdi_nr_reclaimable + bdi_nr_writeback <= bdi_thresh)
> - break;
> + break;
>
> if (!bdi->dirty_exceeded)
> bdi->dirty_exceeded = 1;
> @@ -392,39 +392,34 @@ static void balance_dirty_pages(struct a
> */
> if (bdi_nr_reclaimable) {
> writeback_inodes(&wbc);
> -
> + pages_written += write_chunk - wbc.nr_to_write;
> get_dirty_limits(&background_thresh, &dirty_thresh,
> &bdi_thresh, bdi);
> + }
>
> - /*
> - * In order to avoid the stacked BDI deadlock we need
> - * to ensure we accurately count the 'dirty' pages when
> - * the threshold is low.
> - *
> - * Otherwise it would be possible to get thresh+n pages
> - * reported dirty, even though there are thresh-m pages
> - * actually dirty; with m+n sitting in the percpu
> - * deltas.
> - */
> - if (bdi_thresh < 2*bdi_stat_error(bdi)) {
> - bdi_nr_reclaimable =
> - bdi_stat_sum(bdi, BDI_RECLAIMABLE);
> - bdi_nr_writeback =
> - bdi_stat_sum(bdi, BDI_WRITEBACK);
> - } else {
> - bdi_nr_reclaimable =
> - bdi_stat(bdi, BDI_RECLAIMABLE);
> - bdi_nr_writeback =
> - bdi_stat(bdi, BDI_WRITEBACK);
> - }
> + /*
> + * In order to avoid the stacked BDI deadlock we need
> + * to ensure we accurately count the 'dirty' pages when
> + * the threshold is low.
> + *
> + * Otherwise it would be possible to get thresh+n pages
> + * reported dirty, even though there are thresh-m pages
> + * actually dirty; with m+n sitting in the percpu
> + * deltas.
> + */
> + if (bdi_thresh < 2*bdi_stat_error(bdi)) {
> + bdi_nr_reclaimable = bdi_stat_sum(bdi, BDI_RECLAIMABLE);
> + bdi_nr_writeback = bdi_stat_sum(bdi, BDI_WRITEBACK);
> + } else if (bdi_nr_reclaimable) {
> + bdi_nr_reclaimable = bdi_stat(bdi, BDI_RECLAIMABLE);
> + bdi_nr_writeback = bdi_stat(bdi, BDI_WRITEBACK);
> + }
>
> - if (bdi_nr_reclaimable + bdi_nr_writeback <= bdi_thresh)
> - break;
> + if (bdi_nr_reclaimable + bdi_nr_writeback <= bdi_thresh)
> + break;
> + if (pages_written >= write_chunk)
> + break; /* We've done our duty */
>
> - pages_written += write_chunk - wbc.nr_to_write;
> - if (pages_written >= write_chunk)
> - break; /* We've done our duty */
> - }
> congestion_wait(WRITE, HZ/10);
> }
>