Re: [PATCH -next 01/13] md: remove rdev flag 'RemoveSynchronized'
From: Yu Kuai
Date: Mon Aug 14 2023 - 21:05:39 EST
Hi,
在 2023/08/15 5:36, NeilBrown 写道:
On Mon, 14 Aug 2023, Song Liu wrote:
+ 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).
We have customers with thousands of members in a raid10. They do
sometimes need to remove half of them. Dropping RemoveSynchronized
would significantly increase the time it takes to do that.
Removing an rdev is not often a hot path. But sometimes it can be.
Thanks for the explanation, and soory that I didn't mention that in this
commit message, the way that rdev is protected through rcu is not safe,
and refer to the implementation of 'q_usage_counter' in block layer, I'm
planing to refactor the way that rdev is protected and rcu is not needed
anymore:
1. refactor mddev_suspend(), and make sure it's called by all the caller
of remove_and_add_spares().
2. factor out a helper md_array_enter() from md_handle_request, this
helper will grab 'active_io' and wait for mddev_suspend() to be done.
3. in the fastpath, before accessing rdev, make sure md_array_enter() is
called.
Thanks,
Kuai
NeilBrown
Thanks,
Song
On Thu, Aug 3, 2023 at 9:27 PM Yu Kuai <yukuai1@xxxxxxxxxxxxxxx> wrote:
From: Yu Kuai <yukuai3@xxxxxxxxxx>
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@xxxxxxxxxx>
---
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
.