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Message-ID: <CAPhsuW5m0bzO_FKw4VxE9S4KK6p7EZaffX+ZoYJZ6VGZQrf1hQ@mail.gmail.com>
Date: Mon, 14 Aug 2023 18:02:46 +0800
From: Song Liu <song@...nel.org>
To: Yu Kuai <yukuai1@...weicloud.com>, NeilBrown <neil@...wn.name>,
NeilBrown <neilb@...e.de>
Cc: xni@...hat.com, linux-raid@...r.kernel.org,
linux-kernel@...r.kernel.org, yukuai3@...wei.com,
yi.zhang@...wei.com, yangerkun@...wei.com
Subject: Re: [PATCH -next 01/13] md: remove rdev flag 'RemoveSynchronized'
+ Neil
RemoveSynchronized was added by Neil not too long ago. I wonder whether
we still need it in some cases (large raid10 losing a large set of disks).
Thanks,
Song
On Thu, Aug 3, 2023 at 9:27 PM Yu Kuai <yukuai1@...weicloud.com> wrote:
>
> From: Yu Kuai <yukuai3@...wei.com>
>
> When multiple rdevs are removed from array in remove_and_add_spares(),
> which is only possible from daemon thread(user can only remove one rdev
> through ioctl/sysfs at one time), the flag is used to avoid calling
> synchronize_rcu() multiple times for each rdev.
>
> However, remove rdev from daemon thread really is super cold path, while
> removing n rdevs, it doesn't matter sync rcu n times or just one time.
> Hence remove this flag and make code simpler.
>
> Signed-off-by: Yu Kuai <yukuai3@...wei.com>
> ---
> drivers/md/md-multipath.c | 15 +++++++--------
> drivers/md/md.c | 26 ++------------------------
> drivers/md/md.h | 5 -----
> drivers/md/raid1.c | 15 +++++++--------
> drivers/md/raid10.c | 15 +++++++--------
> drivers/md/raid5.c | 15 +++++++--------
> 6 files changed, 30 insertions(+), 61 deletions(-)
>
> diff --git a/drivers/md/md-multipath.c b/drivers/md/md-multipath.c
> index d22276870283..9e4ddd5240cd 100644
> --- a/drivers/md/md-multipath.c
> +++ b/drivers/md/md-multipath.c
> @@ -258,14 +258,13 @@ static int multipath_remove_disk(struct mddev *mddev, struct md_rdev *rdev)
> goto abort;
> }
> p->rdev = NULL;
> - if (!test_bit(RemoveSynchronized, &rdev->flags)) {
> - synchronize_rcu();
> - if (atomic_read(&rdev->nr_pending)) {
> - /* lost the race, try later */
> - err = -EBUSY;
> - p->rdev = rdev;
> - goto abort;
> - }
> +
> + synchronize_rcu();
> + if (atomic_read(&rdev->nr_pending)) {
> + /* lost the race, try later */
> + err = -EBUSY;
> + p->rdev = rdev;
> + goto abort;
> }
> err = md_integrity_register(mddev);
> }
> diff --git a/drivers/md/md.c b/drivers/md/md.c
> index a3d98273b295..cd7ac1dee3b8 100644
> --- a/drivers/md/md.c
> +++ b/drivers/md/md.c
> @@ -9155,7 +9155,6 @@ static int remove_and_add_spares(struct mddev *mddev,
> struct md_rdev *rdev;
> int spares = 0;
> int removed = 0;
> - bool remove_some = false;
>
> if (this && test_bit(MD_RECOVERY_RUNNING, &mddev->recovery))
> /* Mustn't remove devices when resync thread is running */
> @@ -9165,28 +9164,9 @@ static int remove_and_add_spares(struct mddev *mddev,
> if ((this == NULL || rdev == this) &&
> rdev->raid_disk >= 0 &&
> !test_bit(Blocked, &rdev->flags) &&
> - test_bit(Faulty, &rdev->flags) &&
> + !test_bit(In_sync, &rdev->flags) &&
> + !test_bit(Journal, &rdev->flags) &&
> atomic_read(&rdev->nr_pending)==0) {
> - /* Faulty non-Blocked devices with nr_pending == 0
> - * never get nr_pending incremented,
> - * never get Faulty cleared, and never get Blocked set.
> - * So we can synchronize_rcu now rather than once per device
> - */
> - remove_some = true;
> - set_bit(RemoveSynchronized, &rdev->flags);
> - }
> - }
> -
> - if (remove_some)
> - synchronize_rcu();
> - rdev_for_each(rdev, mddev) {
> - if ((this == NULL || rdev == this) &&
> - rdev->raid_disk >= 0 &&
> - !test_bit(Blocked, &rdev->flags) &&
> - ((test_bit(RemoveSynchronized, &rdev->flags) ||
> - (!test_bit(In_sync, &rdev->flags) &&
> - !test_bit(Journal, &rdev->flags))) &&
> - atomic_read(&rdev->nr_pending)==0)) {
> if (mddev->pers->hot_remove_disk(
> mddev, rdev) == 0) {
> sysfs_unlink_rdev(mddev, rdev);
> @@ -9195,8 +9175,6 @@ static int remove_and_add_spares(struct mddev *mddev,
> removed++;
> }
> }
> - if (remove_some && test_bit(RemoveSynchronized, &rdev->flags))
> - clear_bit(RemoveSynchronized, &rdev->flags);
> }
>
> if (removed && mddev->kobj.sd)
> diff --git a/drivers/md/md.h b/drivers/md/md.h
> index 8ae957480976..b25b6d061372 100644
> --- a/drivers/md/md.h
> +++ b/drivers/md/md.h
> @@ -189,11 +189,6 @@ enum flag_bits {
> * than other devices in the array
> */
> ClusterRemove,
> - RemoveSynchronized, /* synchronize_rcu() was called after
> - * this device was known to be faulty,
> - * so it is safe to remove without
> - * another synchronize_rcu() call.
> - */
> ExternalBbl, /* External metadata provides bad
> * block management for a disk
> */
> diff --git a/drivers/md/raid1.c b/drivers/md/raid1.c
> index 23d211969565..acb6d6542619 100644
> --- a/drivers/md/raid1.c
> +++ b/drivers/md/raid1.c
> @@ -1859,15 +1859,14 @@ static int raid1_remove_disk(struct mddev *mddev, struct md_rdev *rdev)
> goto abort;
> }
> p->rdev = NULL;
> - if (!test_bit(RemoveSynchronized, &rdev->flags)) {
> - synchronize_rcu();
> - if (atomic_read(&rdev->nr_pending)) {
> - /* lost the race, try later */
> - err = -EBUSY;
> - p->rdev = rdev;
> - goto abort;
> - }
> + synchronize_rcu();
> + if (atomic_read(&rdev->nr_pending)) {
> + /* lost the race, try later */
> + err = -EBUSY;
> + p->rdev = rdev;
> + goto abort;
> }
> +
> if (conf->mirrors[conf->raid_disks + number].rdev) {
> /* We just removed a device that is being replaced.
> * Move down the replacement. We drain all IO before
> diff --git a/drivers/md/raid10.c b/drivers/md/raid10.c
> index 7704a4c7f469..64dd5cb6133e 100644
> --- a/drivers/md/raid10.c
> +++ b/drivers/md/raid10.c
> @@ -2247,15 +2247,14 @@ static int raid10_remove_disk(struct mddev *mddev, struct md_rdev *rdev)
> goto abort;
> }
> *rdevp = NULL;
> - if (!test_bit(RemoveSynchronized, &rdev->flags)) {
> - synchronize_rcu();
> - if (atomic_read(&rdev->nr_pending)) {
> - /* lost the race, try later */
> - err = -EBUSY;
> - *rdevp = rdev;
> - goto abort;
> - }
> + synchronize_rcu();
> + if (atomic_read(&rdev->nr_pending)) {
> + /* lost the race, try later */
> + err = -EBUSY;
> + *rdevp = rdev;
> + goto abort;
> }
> +
> if (p->replacement) {
> /* We must have just cleared 'rdev' */
> p->rdev = p->replacement;
> diff --git a/drivers/md/raid5.c b/drivers/md/raid5.c
> index 4cdb35e54251..37d9865b180a 100644
> --- a/drivers/md/raid5.c
> +++ b/drivers/md/raid5.c
> @@ -8267,15 +8267,14 @@ static int raid5_remove_disk(struct mddev *mddev, struct md_rdev *rdev)
> goto abort;
> }
> *rdevp = NULL;
> - if (!test_bit(RemoveSynchronized, &rdev->flags)) {
> - lockdep_assert_held(&mddev->reconfig_mutex);
> - synchronize_rcu();
> - if (atomic_read(&rdev->nr_pending)) {
> - /* lost the race, try later */
> - err = -EBUSY;
> - rcu_assign_pointer(*rdevp, rdev);
> - }
> + lockdep_assert_held(&mddev->reconfig_mutex);
> + synchronize_rcu();
> + if (atomic_read(&rdev->nr_pending)) {
> + /* lost the race, try later */
> + err = -EBUSY;
> + rcu_assign_pointer(*rdevp, rdev);
> }
> +
> if (!err) {
> err = log_modify(conf, rdev, false);
> if (err)
> --
> 2.39.2
>
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