md: reduce the number of synchronize_rcu() calls when multiple devices fail.
Every time a device is removed with ->hot_remove_disk() a synchronize_rcu() call is made
which can delay several milliseconds in some case.
If lots of devices fail at once - as could happen with a large RAID10 where one set
of devices are removed all at once - these delays can add up to be very inconcenient.
As failure is not reversible we can check for that first, setting a
separate flag if it is found, and then all synchronize_rcu() once for
all the flagged devices. Then ->hot_remove_disk() function can skip the
synchronize_rcu() step if the flag is set.
fix build error(Shaohua)
Signed-off-by: NeilBrown <neilb@suse.com>
Signed-off-by: Shaohua Li <shli@fb.com>
diff --git a/drivers/md/raid1.c b/drivers/md/raid1.c
index 34f20c0..5027ef4 100644
--- a/drivers/md/raid1.c
+++ b/drivers/md/raid1.c
@@ -1656,13 +1656,16 @@
goto abort;
}
p->rdev = NULL;
- synchronize_rcu();
- if (atomic_read(&rdev->nr_pending)) {
- /* lost the race, try later */
- err = -EBUSY;
- p->rdev = rdev;
- goto abort;
- } else if (conf->mirrors[conf->raid_disks + number].rdev) {
+ 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;
+ }
+ }
+ 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
* doing this to avoid confusion.