commit ccfc7bf1f0 points out bios from conf->bio_end_io_list also
contribute to conf->nr_queued counter, that's right. But the fix
could be improved. The original fix replaces list_add() by a while()
loop to iterate every bio on conf->bio_end_io_list, and decrease
conf->nr_queued. If we look at the code several lines after, we may
find there is another while() loop to iterate every node from tmp
list which contains the original content of conf->bio_end_io_list.
Yes, we can decrease conf->nr_queued here, then we can avoid the
previous extra while() loop, which consumes more CPU cycles and hold
a spin lock longer time when conf->bio_end_io_list is not tiny.
This patch changes to decrease conf->nr_queued in loop of
while(!list_empty(&tmp)){}, it avoids an extra loop execution, and
avoids holding conf->device_lock for too long time.
By suggestion from Neil, in this version of the patch, I use
list_splice_init() interface to operate conf->bio_end_io_list.
Signed-off-by: Coly Li <colyli@xxxxxxx>
Cc: Shaohua Li <shli@xxxxxx>
Cc: Neil Brown <neilb@xxxxxxx>
---
drivers/md/raid1.c | 9 +++++----
1 file changed, 5 insertions(+), 4 deletions(-)
Index: linux-raid1/drivers/md/raid1.c
===================================================================
--- linux-raid1.orig/drivers/md/raid1.c
+++ linux-raid1/drivers/md/raid1.c
@@ -2387,17 +2387,17 @@ static void raid1d(struct md_thread *thr
!test_bit(MD_CHANGE_PENDING, &mddev->flags)) {
LIST_HEAD(tmp);
spin_lock_irqsave(&conf->device_lock, flags);
- if (!test_bit(MD_CHANGE_PENDING, &mddev->flags)) {
- while (!list_empty(&conf->bio_end_io_list)) {
- list_move(conf->bio_end_io_list.prev, &tmp);
- conf->nr_queued--;
- }
- }
+ if (!test_bit(MD_CHANGE_PENDING, &mddev->flags))
+ list_splice_init(&conf->bio_end_io_list, &tmp);
spin_unlock_irqrestore(&conf->device_lock, flags);
+
while (!list_empty(&tmp)) {
r1_bio = list_first_entry(&tmp, struct r1bio,
retry_list);
list_del(&r1_bio->retry_list);
+ spin_lock_irqsave(&conf->device_lock, flags);
+ conf->nr_queued--;
+ spin_unlock_irqrestore(&conf->device_lock, flags);
if (mddev->degraded)
set_bit(R1BIO_Degraded, &r1_bio->state);
if (test_bit(R1BIO_WriteError, &r1_bio->state))
--
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