Re: bcache strange behaviour in write back mode

[Jack Wang <jinpu.wang-EIkl63zCoXaH+58JC4qpiA@public.gmane.org>]

I revert this commit:

diff --git a/drivers/md/bcache/request.c b/drivers/md/bcache/request.c
index e5ff12e..2f36743 100644
--- a/drivers/md/bcache/request.c
+++ b/drivers/md/bcache/request.c
@@ -489,6 +489,12 @@ static void bch_insert_data_loop(struct closure *cl)
 		bch_queue_gc(op->c);
 	}

+	/*
+	 * Journal writes are marked REQ_FLUSH; if the original write was a
+	 * flush, it'll wait on the journal write.
+	 */
+	bio->bi_rw &= ~(REQ_FLUSH|REQ_FUA);
+
 	do {
 		unsigned i;
 		struct bkey *k;
@@ -716,7 +722,7 @@ static struct search *search_alloc(struct bio *bio,
struct bcache_device *d)
 	s->task			= current;
 	s->orig_bio		= bio;
 	s->write		= (bio->bi_rw & REQ_WRITE) != 0;
-	s->op.flush_journal	= (bio->bi_rw & REQ_FLUSH) != 0;
+	s->op.flush_journal	= (bio->bi_rw & (REQ_FLUSH|REQ_FUA)) != 0;
 	s->op.skip		= (bio->bi_rw & REQ_DISCARD) != 0;
 	s->recoverable		= 1;
 	s->start_time		= jiffies;
diff --git a/drivers/md/bcache/super.c b/drivers/md/bcache/super.c
index 6817ea4..0932580 100644
--- a/drivers/md/bcache/super.c
+++ b/drivers/md/bcache/super.c
@@ -766,6 +766,8 @@ static int bcache_device_init(struct bcache_device
*d, unsigned block_size)
 	set_bit(QUEUE_FLAG_NONROT,	&d->disk->queue->queue_flags);
 	set_bit(QUEUE_FLAG_DISCARD,	&d->disk->queue->queue_flags);

+	blk_queue_flush(q, REQ_FLUSH|REQ_FUA);
+
 	return 0;
 }

the strange behaviour is gone. And I checked the bcache-testing, it does
not contain that commit any more, maybe I'm lost in the git tree update.
Anyway, thanks Kent for your kindly support.

Jack

On 2013年04月22日 21:15, Jack Wang wrote:
> Hi all,
> 
> We've seen strange behaviour in bcache mode in current bcache-testing
> branch with Possible allocator fix:
> 
> Once I start writing data with "dd if=/dev/zero of=/dev/bcache0 bs=4k
> count=10000 oflag=sync", all SSDs in the Pool go close to 100% util and
> I see about 3600 writes/second in iostat for each disk in the pool, BUT
> no data written in means of throughput.
> 
> Then after some seconds (the flush interval of bcache) I see the flush
> of the writeback and also data written to the pool SSDs which looks
> pretty much like reordering and merging happened for that data.
> 
> bcache-3.2 does not have such problem.
> only bcache(master) and bcache-testing have such problem.
> 
> What's the possible reason?
> 
> Regards,
> Jack
>