From: Tang Junhui <tang.junhui@xxxxxxxxxx>
I noticed you add "closure_sync(&cl)" before assigning delay to zero in your patch,
I think we should add it before:
delay = writeback_delay(dc, size)
otherwise we would alays get a wrong value of delay after calling writeback_delay(),
since the write-back IO is just sended out and not finished yet.
Am I right?
>If the control system would wait for at least half a second, and there's
>been no reqs hitting the backing disk for awhile: use an alternate mode
>where we have at most one contiguous set of writebacks in flight at a
>time. (But don't otherwise delay). If front-end IO appears, it will
>still be quick, as it will only have to contend with one real operation
>in flight. But otherwise, we'll be sending data to the backing disk as
>quickly as it can accept it (with one op at a time).
>
>Signed-off-by: Michael Lyle <mlyle@xxxxxxxx>
>---
> drivers/md/bcache/bcache.h | 7 +++++++
> drivers/md/bcache/request.c | 1 +
> drivers/md/bcache/writeback.c | 21 +++++++++++++++++++++
> 3 files changed, 29 insertions(+)
>
>diff --git a/drivers/md/bcache/bcache.h b/drivers/md/bcache/bcache.h
>index 3be0fcc19b1f..5f7b0b2513cc 100644
>--- a/drivers/md/bcache/bcache.h
>+++ b/drivers/md/bcache/bcache.h
>@@ -320,6 +320,13 @@ struct cached_dev {
> */
> atomic_t has_dirty;
>
>+ /*
>+ * Set to zero by things that touch the backing volume-- except
>+ * writeback. Incremented by writeback. Used to determine when to
>+ * accelerate idle writeback.
>+ */
>+ atomic_t backing_idle;
>+
> struct bch_ratelimit writeback_rate;
> struct delayed_work writeback_rate_update;
>
>diff --git a/drivers/md/bcache/request.c b/drivers/md/bcache/request.c
>index d1faaba6b93f..3b4defbdcbbd 100644
>--- a/drivers/md/bcache/request.c
>+++ b/drivers/md/bcache/request.c
>@@ -996,6 +996,7 @@ static blk_qc_t cached_dev_make_request(struct request_queue *q,
> struct cached_dev *dc = container_of(d, struct cached_dev, disk);
> int rw = bio_data_dir(bio);
>
>+ atomic_set(&dc->backing_idle, 0);
> generic_start_io_acct(q, rw, bio_sectors(bio), &d->disk->part0);
>
> bio_set_dev(bio, dc->bdev);
>diff --git a/drivers/md/bcache/writeback.c b/drivers/md/bcache/writeback.c
>index 4084586d5991..bf309a480335 100644
>--- a/drivers/md/bcache/writeback.c
>+++ b/drivers/md/bcache/writeback.c
>@@ -383,6 +383,27 @@ static void read_dirty(struct cached_dev *dc)
>
> delay = writeback_delay(dc, size);
>
>+ /* If the control system would wait for at least half a
>+ * second, and there's been no reqs hitting the backing disk
>+ * for awhile: use an alternate mode where we have at most
>+ * one contiguous set of writebacks in flight at a time. If
>+ * someone wants to do IO it will be quick, as it will only
>+ * have to contend with one operation in flight, and we'll
>+ * be round-tripping data to the backing disk as quickly as
>+ * it can accept it.
>+ */
>+ if (delay >= HZ / 2) {
>+ /* 3 means at least 1.5 seconds, up to 7.5 if we
>+ * have slowed way down.
>+ */
>+ if (atomic_inc_return(&dc->backing_idle) >= 3) {
>+ /* Wait for current I/Os to finish */
>+ closure_sync(&cl);
>+ /* And immediately launch a new set. */
>+ delay = 0;
>+ }
>+ }
>+
> while (!kthread_should_stop() && delay) {
> schedule_timeout_interruptible(delay);
> delay = writeback_delay(dc, 0);
>--
Thanks,
Tang Junhui
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