Re: [PATCH 2/5] block: add request->io_data_len

[Ming Lei]

Hi Tejun,

On Wed, Apr 08, 2020 at 04:14:47PM -0400, Tejun Heo wrote:
> Currently, at the time of completeion, there's no way of knowing how big a
> request was. blk-iocost will need this information to account for IO size when
> calculating expected latencies.
> 
> This patch adds rq->io_data_len which remembers blk_rq_bytes() at the time the
> request gets issued. The field is enabled iff CONFIG_BLK_IO_DATA_LEN is set and
> doesn't increase the size of the struct even when enabled.

Almost all __blk_mq_end_request() follow blk_update_request(), so the
completed bytes can be passed to __blk_mq_end_request(), then we can
avoid to introduce this field.

Also there is just 20 callers of __blk_mq_end_request(), looks this kind
of change shouldn't be too big.


Thanks, 
Ming