Re: [md PATCH 10/15] md/raid1: stop using bi_phys_segment

[NeilBrown <neilb@suse.com>]

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On Wed, Mar 15 2017, Shaohua Li wrote:

> On Wed, Mar 15, 2017 at 02:05:14PM +1100, Neil Brown wrote:
>> Change to use bio->__bi_remaining to count number of r1bio attached
>> to a bio.
>> See precious raid10 patch for more details.
>> 
>> Like the raid10.c patch, this fixes a bug as nr_queued and nr_pending
>> used to measure different things, but were being compared.
>> 
>> This patch fixes another bug in that nr_pending previously did not
>> could write-behind requests, so behind writes could continue while
>> resync was happening.  How that nr_pending counts all r1_bio,
>> the resync cannot commence until the behind writes have completed.
>> 
>> Signed-off-by: NeilBrown <neilb@suse.com>
>> ---
>>  drivers/md/raid1.c |   87 +++++++++++++---------------------------------------
>>  1 file changed, 22 insertions(+), 65 deletions(-)
>> 
>> diff --git a/drivers/md/raid1.c b/drivers/md/raid1.c
>> index 7e509a894f15..e566407b196f 100644
>> --- a/drivers/md/raid1.c
>> +++ b/drivers/md/raid1.c
>> @@ -246,35 +246,18 @@ static void reschedule_retry(struct r1bio *r1_bio)
>>  static void call_bio_endio(struct r1bio *r1_bio)
>>  {
>>  	struct bio *bio = r1_bio->master_bio;
>> -	int done;
>>  	struct r1conf *conf = r1_bio->mddev->private;
>>  	sector_t bi_sector = bio->bi_iter.bi_sector;
>>  
>> -	if (bio->bi_phys_segments) {
>> -		unsigned long flags;
>> -		spin_lock_irqsave(&conf->device_lock, flags);
>> -		bio->bi_phys_segments--;
>> -		done = (bio->bi_phys_segments == 0);
>> -		spin_unlock_irqrestore(&conf->device_lock, flags);
>> -		/*
>> -		 * make_request() might be waiting for
>> -		 * bi_phys_segments to decrease
>> -		 */
>> -		wake_up(&conf->wait_barrier);
>> -	} else
>> -		done = 1;
>> -
>>  	if (!test_bit(R1BIO_Uptodate, &r1_bio->state))
>>  		bio->bi_error = -EIO;
>>  
>> -	if (done) {
>> -		bio_endio(bio);
>> -		/*
>> -		 * Wake up any possible resync thread that waits for the device
>> -		 * to go idle.
>> -		 */
>> -		allow_barrier(conf, bi_sector);
>> -	}
>> +	bio_endio(bio);
>> +	/*
>> +	 * Wake up any possible resync thread that waits for the device
>> +	 * to go idle.
>> +	 */
>> +	allow_barrier(conf, bi_sector);
>
> I think this one should be r1_bio->sector instead of master_bio->sector,
> because multiple r1_bio could be attached to a master_bio. Maybe not change
> anything, because both sector should be in the same barrier unit, but we'd
> better to be consistent.

Yes, I agree.  Both that it won't make a practical difference and that
it should be changed.
I just noticed another little problem with this patch.
The chunk in handle_read_error() should have added inc_pending()
near where it added bio_inc_remaining().

Shall I just resend the individual patch (and the raid5 one?).

Thanks,
NeilBrown

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