[PATCH v2 2/5] block: add support for REQ_OP_WRITE_ZEROES

[chaitany kulkarni]

Sounds good, I'll update the whole series and resend it with v2 prefix.



On Thu, Nov 17, 2016 at 11:46 PM, Christoph Hellwig <hch at infradead.org> wrote:
> On Thu, Nov 17, 2016 at 02:17:11PM -0800, Chaitanya Kulkarni wrote:
>> From: Chaitanya Kulkarni <chaitanya.kulkarni at hgst.com>
>>
>> This adds a new block layer operation to zero out a range of
>> LBAs. This allows to implement zeroing for devices that don't use
>> either discard with a predictable zero pattern or WRITE SAME of zeroes.
>> The prominent example of that is NVMe with the Write Zeroes command,
>> but in the future this should also help with improving the way
>> zeroing discards work.
>>
>> Signed-off-by: Chaitanya Kulkarni <chaitanya.kulkarni at hgst.com>
>
> I think you'll need to resend the whole series so that nvme can set
> the maximum discard sectors value.
>
>> @@ -575,9 +575,10 @@ static inline bool wbt_should_throttle(struct rq_wb *rwb, struct bio *bio)
>>       const int op = bio_op(bio);
>>
>>       /*
>> -      * If not a WRITE (or a discard), do nothing
>> +      * If not a WRITE (or a discard or write zeroes), do nothing
>>        */
>> -     if (!(op == REQ_OP_WRITE || op == REQ_OP_DISCARD))
>> +     if (!(op == REQ_OP_WRITE || op == REQ_OP_DISCARD ||
>> +                             op == REQ_OP_WRITE_ZEROES))
>>               return false;
>
> Jens: should we really throttle for discard or write zeroes here?
> Those aren't really writeback driven..
>
>> +static inline unsigned int bdev_write_zeroes(struct block_device *bdev)
>> +{
>> +     struct request_queue *q = bdev_get_queue(bdev);
>> +
>> +     if (q)
>> +             return q->limits.max_write_zeroes_sectors;
>> +
>> +     return 0;
>
> If this returns a sector value I'd name it bdev_write_zeroes_sectors.
>
> Otherwise this looks great.