Re: [PATCH 14/14] barriers

[Kiyoshi Ueda <k-ueda@ct.jp.nec.com>]

Hi Mikulas,

Sorry for my less explanation.

On 2009/03/30 23:02 +0900, Mikulas Patocka wrote:
> Hi
> 
> You must apply the whole series of patches from patch 1 (that I sent long 
> time before). This patch is an update to the series.

Yes, I know that.
But the Milan's patch (http://marc.info/?l=dm-devel&m=123695241224620&w=2)
changed around dec_pending() in dm.c and it has already been merged into
2.6.29 (after 2.6.29-rc8).
Your patch conflicts against the change and is rejected, when I try to
apply your whole patch-set on top of 2.6.29.

The conflict may be just cosmetic reasons, but I'm not sure.
So I noticed that to you, so that I can review this patch correctly
for my request-based dm work.

Thanks,
Kiyoshi Ueda


> Mikulas
> 
>> Hi Mikulas,
>>
>> This patch doesn't apply to 2.6.29.
>> Probably you are using a pretty older kernel?
>>
>> Thanks,
>> Kiyoshi Ueda
>>
>>
>> On 2009/03/27 15:11 +0900, Mikulas Patocka wrote:
>>> Barrier support.
>>>
>>> Barriers are submitted to a worker thread that issues them in-order.
>>>
>>> __split_and_process_bio function is modified that when it sees a barrier
>>> request, it waits for all pending IO before the request, then submits
>>> the barrier and waits for it (we must wait, otherwise it could be
>>> intermixed with following requests).
>>>
>>> Errors from the barrier request are recorded in per-device barrier_error
>>> variable. There may be only one barrier request in progress, so using
>>> a per-device variable is correct.
>>>
>>> The barrier request is converted to non-barrier request when sending it
>>> to the underlying device.
>>>
>>> This patch guarantees correct barrier behavior if the underlying device
>>> doesn't perform write-back caching. The same requirement existed before
>>> barriers were supported in dm.
>>>
>>> Bottom layer barrier support (sending barriers by target drivers) and
>>> handling devices with write-back caches will be done in further patches.
>>>
>>> Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
>>>
>>> ---
>>>  drivers/md/dm.c |   79 +++++++++++++++++++++++++++++++++++++++++++-------------
>>>  1 file changed, 61 insertions(+), 18 deletions(-)
>>>
>>> Index: linux-2.6.29-rc8-devel/drivers/md/dm.c
>>> ===================================================================
>>> --- linux-2.6.29-rc8-devel.orig/drivers/md/dm.c	2009-03-27 06:51:29.000000000 +0100
>>> +++ linux-2.6.29-rc8-devel/drivers/md/dm.c	2009-03-27 06:51:33.000000000 +0100
>>> @@ -125,6 +125,11 @@ struct mapped_device {
>>>  	spinlock_t deferred_lock;
>>>  
>>>  	/*
>>> +	 * An error from the barrier request currently being processed.
>>> +	 */
>>> +	int barrier_error;
>>> +
>>> +	/*
>>>  	 * Processing queue (flush/barriers)
>>>  	 */
>>>  	struct workqueue_struct *wq;
>>> @@ -425,6 +430,10 @@ static void end_io_acct(struct dm_io *io
>>>  	part_stat_add(cpu, &dm_disk(md)->part0, ticks[rw], duration);
>>>  	part_stat_unlock();
>>>  
>>> +	/*
>>> +	 * after this is decremented, the bio must not be touched if it is
>>> +	 * barrier bio
>>> +	 */
>>>  	dm_disk(md)->part0.in_flight = pending =
>>>  		atomic_dec_return(&md->pending);
>>>  
>>> @@ -525,19 +534,29 @@ static void dec_pending(struct dm_io *io
>>>  			 */
>>>  			spin_lock_irqsave(&io->md->deferred_lock, flags);
>>>  			if (__noflush_suspending(io->md))
>>> -				bio_list_add(&io->md->deferred, io->bio);
>>> +				bio_list_add_head(&io->md->deferred, io->bio);
>>>  			else
>>>  				/* noflush suspend was interrupted. */
>>>  				io->error = -EIO;
>>>  			spin_unlock_irqrestore(&io->md->deferred_lock, flags);
>>>  		}
>>>  
>>> -		end_io_acct(io);
>>> +		if (bio_barrier(io->bio)) {
>>> +			/*
>>> +			 * There could be just one barrier request, so we use
>>> +			 * per-device variable for error reporting is OK.
>>> +			 * Note that you can't touch the bio after end_io_acct
>>> +			 */
>>> +			io->md->barrier_error = io->error;
>>> +			end_io_acct(io);
>>> +		} else {
>>> +			end_io_acct(io);
>>>  
>>> -		if (io->error != DM_ENDIO_REQUEUE) {
>>> -			trace_block_bio_complete(io->md->queue, io->bio);
>>> +			if (io->error != DM_ENDIO_REQUEUE) {
>>> +				trace_block_bio_complete(io->md->queue, io->bio);
>>>  
>>> -			bio_endio(io->bio, io->error);
>>> +				bio_endio(io->bio, io->error);
>>> +			}
>>>  		}
>>>  
>>>  		free_io(io->md, io);
>>> @@ -682,7 +701,7 @@ static struct bio *split_bvec(struct bio
>>>  
>>>  	clone->bi_sector = sector;
>>>  	clone->bi_bdev = bio->bi_bdev;
>>> -	clone->bi_rw = bio->bi_rw;
>>> +	clone->bi_rw = bio->bi_rw & ~(1 << BIO_RW_BARRIER);
>>>  	clone->bi_vcnt = 1;
>>>  	clone->bi_size = to_bytes(len);
>>>  	clone->bi_io_vec->bv_offset = offset;
>>> @@ -703,6 +722,7 @@ static struct bio *clone_bio(struct bio 
>>>  
>>>  	clone = bio_alloc_bioset(GFP_NOIO, bio->bi_max_vecs, bs);
>>>  	__bio_clone(clone, bio);
>>> +	clone->bi_rw &= ~(1 << BIO_RW_BARRIER);
>>>  	clone->bi_destructor = dm_bio_destructor;
>>>  	clone->bi_sector = sector;
>>>  	clone->bi_idx = idx;
>>> @@ -823,7 +843,10 @@ static void __split_and_process_bio(stru
>>>  
>>>  	ci.map = dm_get_table(md);
>>>  	if (unlikely(!ci.map)) {
>>> -		bio_io_error(bio);
>>> +		if (!bio_barrier(bio))
>>> +			bio_io_error(bio);
>>> +		else
>>> +			md->barrier_error = -EIO;
>>>  		return;
>>>  	}
>>>  
>>> @@ -907,15 +930,6 @@ static int dm_request(struct request_que
>>>  	struct mapped_device *md = q->queuedata;
>>>  	int cpu;
>>>  
>>> -	/*
>>> -	 * There is no use in forwarding any barrier request since we can't
>>> -	 * guarantee it is (or can be) handled by the targets correctly.
>>> -	 */
>>> -	if (unlikely(bio_barrier(bio))) {
>>> -		bio_endio(bio, -EOPNOTSUPP);
>>> -		return 0;
>>> -	}
>>> -
>>>  	down_read(&md->io_lock);
>>>  
>>>  	cpu = part_stat_lock();
>>> @@ -927,7 +941,8 @@ static int dm_request(struct request_que
>>>  	 * If we're suspended or the thread is processing barriers
>>>  	 * we have to queue this io for later.
>>>  	 */
>>> -	if (unlikely(test_bit(DMF_QUEUE_IO_FOR_THREAD, &md->flags))) {
>>> +	if (unlikely(test_bit(DMF_QUEUE_IO_FOR_THREAD, &md->flags)) ||
>>> +	    unlikely(bio_barrier(bio))) {
>>>  		up_read(&md->io_lock);
>>>  
>>>  		if (unlikely(test_bit(DMF_BLOCK_FOR_SUSPEND, &md->flags)) &&
>>> @@ -1393,6 +1408,12 @@ static int dm_wait_for_completion(struct
>>>  	return r;
>>>  }
>>>  
>>> +static int dm_flush(struct mapped_device *md)
>>> +{
>>> +	dm_wait_for_completion(md, TASK_UNINTERRUPTIBLE);
>>> +	return 0;
>>> +}
>>> +
>>>  /*
>>>   * Process the deferred bios
>>>   */
>>> @@ -1415,8 +1436,30 @@ static void dm_wq_work(struct work_struc
>>>  			break;
>>>  		}
>>>  
>>> -		__split_and_process_bio(md, c);
>>> +		if (!bio_barrier(c))
>>> +			__split_and_process_bio(md, c);
>>> +		else {
>>> +			int error = dm_flush(md);
>>> +			if (unlikely(error)) {
>>> +				bio_endio(c, error);
>>> +				goto next_bio;
>>> +			}
>>> +			if (bio_empty_barrier(c)) {
>>> +				bio_endio(c, 0);
>>> +				goto next_bio;
>>> +			}
>>> +
>>> +			__split_and_process_bio(md, c);
>>> +
>>> +			error = dm_flush(md);
>>> +			if (!error && md->barrier_error)
>>> +				error = md->barrier_error;
>>> +
>>> +			if (md->barrier_error != DM_ENDIO_REQUEUE)
>>> +				bio_endio(c, error);
>>> +		}
>>>  
>>> +next_bio:
>>>  		down_write(&md->io_lock);
>>>  	}
>>>  }
>>>
>>> --
>>> dm-devel mailing list
>>> dm-devel@redhat.com
>>> https://www.redhat.com/mailman/listinfo/dm-devel