Re: [md PATCH 02/15] md/raid5: simplfy delaying of writes while metadata is updated.

Shaohua Li
2017-03-15T23:03:56Z

On Wed, Mar 15, 2017 at 02:05:12PM +1100, Neil Brown wrote:
> If a device fails during a write, we must ensure the failure is
> recorded in the metadata before the completion of the write is
> acknowleged.
>
> Commit c3cce6cda162 ("md/raid5: ensure device failure recorded before
> write request returns.") added code for this, but it was
> unnecessarily complicated. We already had similar functionality for
> handling updates to the bad-block-list, thanks to Commit de393cdea66c
> ("md: make it easier to wait for bad blocks to be acknowledged.")
>
> So revert most of the former commit, and instead avoid collecting
> completed writes if MD_CHANGE_PENDING is set. raid5d() will then flush
> the metadata and retry the stripe_head.
> As this change can leave a stripe_head ready for handling immediately
> after handle_active_stripes() returns, we change raid5_do_work() to
> pause when MD_CHANGE_PENDING is set, so that it doesn't spin.
>
> We check MD_CHANGE_PENDING *after* analyse_stripe() as it could be set
> asynchronously. After analyse_stripe(), we have collected stable data
> about the state of devices, which will be used to make decisions.
>
> Signed-off-by: NeilBrown <neilb@suse.com>
> ---
> drivers/md/raid5.c | 31 ++++++++-----------------------
> drivers/md/raid5.h | 3 ---
> 2 files changed, 8 insertions(+), 26 deletions(-)
>
> diff --git a/drivers/md/raid5.c b/drivers/md/raid5.c
> index cc2d039b4aae..f990f74901d2 100644
> --- a/drivers/md/raid5.c
> +++ b/drivers/md/raid5.c
> @@ -4690,7 +4690,8 @@ static void handle_stripe(struct stripe_head *sh)
> if (test_bit(STRIPE_LOG_TRAPPED, &sh->state))
> goto finish;
>
> - if (s.handle_bad_blocks) {
> + if (s.handle_bad_blocks ||
> + test_bit(MD_SB_CHANGE_PENDING, &conf->mddev->sb_flags)) {
> set_bit(STRIPE_HANDLE, &sh->state);
> goto finish;
> }
> @@ -5020,15 +5021,8 @@ static void handle_stripe(struct stripe_head *sh)
> md_wakeup_thread(conf->mddev->thread);
> }
>
> - if (!bio_list_empty(&s.return_bi)) {
> - if (test_bit(MD_SB_CHANGE_PENDING, &conf->mddev->sb_flags)) {
> - spin_lock_irq(&conf->device_lock);
> - bio_list_merge(&conf->return_bi, &s.return_bi);
> - spin_unlock_irq(&conf->device_lock);
> - md_wakeup_thread(conf->mddev->thread);
> - } else
> - return_io(&s.return_bi);
> - }
> + if (!bio_list_empty(&s.return_bi))
> + return_io(&s.return_bi);
>
> clear_bit_unlock(STRIPE_ACTIVE, &sh->state);
> }
> @@ -6225,6 +6219,7 @@ static void raid5_do_work(struct work_struct *work)
> struct r5worker *worker = container_of(work, struct r5worker, work);
> struct r5worker_group *group = worker->group;
> struct r5conf *conf = group->conf;
> + struct mddev *mddev = conf->mddev;
> int group_id = group - conf->worker_groups;
> int handled;
> struct blk_plug plug;
> @@ -6245,6 +6240,9 @@ static void raid5_do_work(struct work_struct *work)
> if (!batch_size && !released)
> break;
> handled += batch_size;
> + wait_event_lock_irq(mddev->sb_wait,
> + !test_bit(MD_SB_CHANGE_DEVS, &mddev->sb_flags),
MD_SB_CHANGE_PENDING?

> + conf->device_lock);
> }
> pr_debug("%d stripes handled\n", handled);
>
> @@ -6272,18 +6270,6 @@ static void raid5d(struct md_thread *thread)
>
> md_check_recovery(mddev);
>
> - if (!bio_list_empty(&conf->return_bi) &&
> - !test_bit(MD_SB_CHANGE_PENDING, &mddev->sb_flags)) {
> - struct bio_list tmp = BIO_EMPTY_LIST;
> - spin_lock_irq(&conf->device_lock);
> - if (!test_bit(MD_SB_CHANGE_PENDING, &mddev->sb_flags)) {
> - bio_list_merge(&tmp, &conf->return_bi);
> - bio_list_init(&conf->return_bi);
> - }
> - spin_unlock_irq(&conf->device_lock);
> - return_io(&tmp);
> - }
> -
> blk_start_plug(&plug);
> handled = 0;
> spin_lock_irq(&conf->device_lock);
> @@ -6935,7 +6921,6 @@ static struct r5conf *setup_conf(struct mddev *mddev)
> INIT_LIST_HEAD(&conf->hold_list);
> INIT_LIST_HEAD(&conf->delayed_list);
> INIT_LIST_HEAD(&conf->bitmap_list);
> - bio_list_init(&conf->return_bi);
> init_llist_head(&conf->released_stripes);
> atomic_set(&conf->active_stripes, 0);
> atomic_set(&conf->preread_active_stripes, 0);
> diff --git a/drivers/md/raid5.h b/drivers/md/raid5.h
> index ba5b7a3790af..13800dc9dd88 100644
> --- a/drivers/md/raid5.h
> +++ b/drivers/md/raid5.h
> @@ -638,9 +638,6 @@ struct r5conf {
> int skip_copy; /* Don't copy data from bio to stripe cache */
> struct list_head *last_hold; /* detect hold_list promotions */
>
> - /* bios to have bi_end_io called after metadata is synced */
> - struct bio_list return_bi;
> -
> atomic_t reshape_stripes; /* stripes with pending writes for reshape */
> /* unfortunately we need two cache names as we temporarily have
> * two caches.
>
>