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

NeilBrown
2017-03-16T02:45:16Z

[-- Attachment #1: Type: text/plain, Size: 5099 bytes --]

On Wed, Mar 15 2017, Shaohua Li wrote:

> 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?

Yes. Thanks for catching.

NeilBrown

>
>> + 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.
>>
>>

[-- Attachment #2: signature.asc --]
[-- Type: application/pgp-signature, Size: 832 bytes --]