Re: bcache strange behaviour in write back mode

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

On 2013年04月24日 22:13, Kent Overstreet wrote:
> Ah, you would've been running an old version of the bcache-testing branch...
> 
> Someone else bisected a different bug to that commit, so that one's
> staying in the dev branch for now.
> 
> I just pushed the allocator fix to the bcache-for-upstream branch, can
> you give that a try?
Yeah, I must seat on an old version.

Sure, will try and report back result.
> 
> On Wed, Apr 24, 2013 at 12:49 PM, Jack Wang <jinpu.wang@profitbricks.com> wrote:
>> 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
>>>
>>
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