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Message-Id: <20240826074843.1575099-1-yukuai1@huaweicloud.com>
Date: Mon, 26 Aug 2024 15:48:43 +0800
From: Yu Kuai <yukuai1@...weicloud.com>
To: song@...nel.org
Cc: linux-raid@...r.kernel.org,
linux-kernel@...r.kernel.org,
yukuai3@...wei.com,
yukuai1@...weicloud.com,
yi.zhang@...wei.com,
yangerkun@...wei.com
Subject: [PATCH md-6.12] md: remove flush handling
From: Yu Kuai <yukuai3@...wei.com>
For flush request, md has a special flush handling to merge concurrent
flush request into single one, however, the whole mechanism is based on
a disk level spin_lock 'mddev->lock'. And fsync can be called quite
often in some user cases, for consequence, spin lock from IO fast path can
cause performance degration.
Fortunately, the block layer already have flush handling to merge
concurrent flush request, and it only acquire hctx level spin lock(see
details in blk-flush.c).
This patch remove the flush handling in md, and convert to use general
block layer flush handling in underlying disks.
Flush test for 4 nvme raid10:
start 128 threads to do fsync 100000 times, on arm64, see how long it
takes.
Test result: about 10 times faster for high concurrency.
Before this patch: 50943374 microseconds
After this patch: 5096347 microseconds
BTW, this patch can fix the same problem as commit 611d5cbc0b35 ("md: fix
deadlock between mddev_suspend and flush bio").
Signed-off-by: Yu Kuai <yukuai3@...wei.com>
---
drivers/md/md.c | 137 ++++--------------------------------------------
drivers/md/md.h | 10 ----
2 files changed, 11 insertions(+), 136 deletions(-)
diff --git a/drivers/md/md.c b/drivers/md/md.c
index a38981de8901..4d675f7cc2a7 100644
--- a/drivers/md/md.c
+++ b/drivers/md/md.c
@@ -546,137 +546,23 @@ static int mddev_set_closing_and_sync_blockdev(struct mddev *mddev, int opener_n
return 0;
}
-/*
- * Generic flush handling for md
- */
-
-static void md_end_flush(struct bio *bio)
-{
- struct md_rdev *rdev = bio->bi_private;
- struct mddev *mddev = rdev->mddev;
-
- bio_put(bio);
-
- rdev_dec_pending(rdev, mddev);
-
- if (atomic_dec_and_test(&mddev->flush_pending))
- /* The pre-request flush has finished */
- queue_work(md_wq, &mddev->flush_work);
-}
-
-static void md_submit_flush_data(struct work_struct *ws);
-
-static void submit_flushes(struct work_struct *ws)
+bool md_flush_request(struct mddev *mddev, struct bio *bio)
{
- struct mddev *mddev = container_of(ws, struct mddev, flush_work);
struct md_rdev *rdev;
+ struct bio *new;
- mddev->start_flush = ktime_get_boottime();
- INIT_WORK(&mddev->flush_work, md_submit_flush_data);
- atomic_set(&mddev->flush_pending, 1);
- rcu_read_lock();
- rdev_for_each_rcu(rdev, mddev)
- if (rdev->raid_disk >= 0 &&
- !test_bit(Faulty, &rdev->flags)) {
- struct bio *bi;
-
- atomic_inc(&rdev->nr_pending);
- rcu_read_unlock();
- bi = bio_alloc_bioset(rdev->bdev, 0,
- REQ_OP_WRITE | REQ_PREFLUSH,
- GFP_NOIO, &mddev->bio_set);
- bi->bi_end_io = md_end_flush;
- bi->bi_private = rdev;
- atomic_inc(&mddev->flush_pending);
- submit_bio(bi);
- rcu_read_lock();
- }
- rcu_read_unlock();
- if (atomic_dec_and_test(&mddev->flush_pending))
- queue_work(md_wq, &mddev->flush_work);
-}
-
-static void md_submit_flush_data(struct work_struct *ws)
-{
- struct mddev *mddev = container_of(ws, struct mddev, flush_work);
- struct bio *bio = mddev->flush_bio;
-
- /*
- * must reset flush_bio before calling into md_handle_request to avoid a
- * deadlock, because other bios passed md_handle_request suspend check
- * could wait for this and below md_handle_request could wait for those
- * bios because of suspend check
- */
- spin_lock_irq(&mddev->lock);
- mddev->prev_flush_start = mddev->start_flush;
- mddev->flush_bio = NULL;
- spin_unlock_irq(&mddev->lock);
- wake_up(&mddev->sb_wait);
-
- if (bio->bi_iter.bi_size == 0) {
- /* an empty barrier - all done */
- bio_endio(bio);
- } else {
- bio->bi_opf &= ~REQ_PREFLUSH;
-
- /*
- * make_requst() will never return error here, it only
- * returns error in raid5_make_request() by dm-raid.
- * Since dm always splits data and flush operation into
- * two separate io, io size of flush submitted by dm
- * always is 0, make_request() will not be called here.
- */
- if (WARN_ON_ONCE(!mddev->pers->make_request(mddev, bio)))
- bio_io_error(bio);
- }
-
- /* The pair is percpu_ref_get() from md_flush_request() */
- percpu_ref_put(&mddev->active_io);
-}
+ rdev_for_each(rdev, mddev) {
+ if (rdev->raid_disk < 0 || test_bit(Faulty, &rdev->flags))
+ continue;
-/*
- * Manages consolidation of flushes and submitting any flushes needed for
- * a bio with REQ_PREFLUSH. Returns true if the bio is finished or is
- * being finished in another context. Returns false if the flushing is
- * complete but still needs the I/O portion of the bio to be processed.
- */
-bool md_flush_request(struct mddev *mddev, struct bio *bio)
-{
- ktime_t req_start = ktime_get_boottime();
- spin_lock_irq(&mddev->lock);
- /* flush requests wait until ongoing flush completes,
- * hence coalescing all the pending requests.
- */
- wait_event_lock_irq(mddev->sb_wait,
- !mddev->flush_bio ||
- ktime_before(req_start, mddev->prev_flush_start),
- mddev->lock);
- /* new request after previous flush is completed */
- if (ktime_after(req_start, mddev->prev_flush_start)) {
- WARN_ON(mddev->flush_bio);
- /*
- * Grab a reference to make sure mddev_suspend() will wait for
- * this flush to be done.
- *
- * md_flush_reqeust() is called under md_handle_request() and
- * 'active_io' is already grabbed, hence percpu_ref_is_zero()
- * won't pass, percpu_ref_tryget_live() can't be used because
- * percpu_ref_kill() can be called by mddev_suspend()
- * concurrently.
- */
- WARN_ON(percpu_ref_is_zero(&mddev->active_io));
- percpu_ref_get(&mddev->active_io);
- mddev->flush_bio = bio;
- spin_unlock_irq(&mddev->lock);
- INIT_WORK(&mddev->flush_work, submit_flushes);
- queue_work(md_wq, &mddev->flush_work);
- return true;
+ new = bio_alloc_bioset(rdev->bdev, 0,
+ REQ_OP_WRITE | REQ_PREFLUSH, GFP_NOIO,
+ &mddev->bio_set);
+ bio_chain(new, bio);
+ submit_bio(new);
}
- /* flush was performed for some other bio while we waited. */
- spin_unlock_irq(&mddev->lock);
- if (bio->bi_iter.bi_size == 0) {
- /* pure flush without data - all done */
+ if (bio_sectors(bio) == 0) {
bio_endio(bio);
return true;
}
@@ -763,7 +649,6 @@ int mddev_init(struct mddev *mddev)
atomic_set(&mddev->openers, 0);
atomic_set(&mddev->sync_seq, 0);
spin_lock_init(&mddev->lock);
- atomic_set(&mddev->flush_pending, 0);
init_waitqueue_head(&mddev->sb_wait);
init_waitqueue_head(&mddev->recovery_wait);
mddev->reshape_position = MaxSector;
diff --git a/drivers/md/md.h b/drivers/md/md.h
index 1c6a5f41adca..5d2e6bd58e4d 100644
--- a/drivers/md/md.h
+++ b/drivers/md/md.h
@@ -572,16 +572,6 @@ struct mddev {
*/
struct bio_set io_clone_set;
- /* Generic flush handling.
- * The last to finish preflush schedules a worker to submit
- * the rest of the request (without the REQ_PREFLUSH flag).
- */
- struct bio *flush_bio;
- atomic_t flush_pending;
- ktime_t start_flush, prev_flush_start; /* prev_flush_start is when the previous completed
- * flush was started.
- */
- struct work_struct flush_work;
struct work_struct event_work; /* used by dm to report failure event */
mempool_t *serial_info_pool;
void (*sync_super)(struct mddev *mddev, struct md_rdev *rdev);
--
2.39.2
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