On 10/29/18 9:51 AM, Mike Snitzer wrote:
> On Mon, Oct 29 2018 at 10:25am -0400,
> Jens Axboe <axboe@xxxxxxxxx> wrote:
>
>> On 10/29/18 1:10 AM, Hannes Reinecke wrote:
>>> On 10/25/18 11:10 PM, Jens Axboe wrote:
>>>> Nobody sets the helper, so we always return 0. Kill it.
>>>>
>>>> Signed-off-by: Jens Axboe <axboe@xxxxxxxxx>
>>>> ---
>>>> block/blk-core.c | 28 ----------------------------
>>>> block/blk-settings.c | 6 ------
>>>> drivers/md/dm-mpath.c | 4 +---
>>>> include/linux/blkdev.h | 4 ----
>>>> 4 files changed, 1 insertion(+), 41 deletions(-)
>>>>
>>>> diff --git a/block/blk-core.c b/block/blk-core.c
>>>> index 4c39c7865f9c..dd1328f4dc31 100644
>>>> --- a/block/blk-core.c
>>>> +++ b/block/blk-core.c
>>>> @@ -1795,34 +1795,6 @@ void rq_flush_dcache_pages(struct request *rq)
>>>> EXPORT_SYMBOL_GPL(rq_flush_dcache_pages);
>>>> #endif
>>>>
>>>> -/**
>>>> - * blk_lld_busy - Check if underlying low-level drivers of a device are busy
>>>> - * @q : the queue of the device being checked
>>>> - *
>>>> - * Description:
>>>> - * Check if underlying low-level drivers of a device are busy.
>>>> - * If the drivers want to export their busy state, they must set own
>>>> - * exporting function using blk_queue_lld_busy() first.
>>>> - *
>>>> - * Basically, this function is used only by request stacking drivers
>>>> - * to stop dispatching requests to underlying devices when underlying
>>>> - * devices are busy. This behavior helps more I/O merging on the queue
>>>> - * of the request stacking driver and prevents I/O throughput regression
>>>> - * on burst I/O load.
>>>> - *
>>>> - * Return:
>>>> - * 0 - Not busy (The request stacking driver should dispatch request)
>>>> - * 1 - Busy (The request stacking driver should stop dispatching request)
>>>> - */
>>>> -int blk_lld_busy(struct request_queue *q)
>>>> -{
>>>> - if (q->lld_busy_fn)
>>>> - return q->lld_busy_fn(q);
>>>> -
>>>> - return 0;
>>>> -}
>>>> -EXPORT_SYMBOL_GPL(blk_lld_busy);
>>>> -
>>>> /**
>>>> * blk_rq_unprep_clone - Helper function to free all bios in a cloned request
>>>> * @rq: the clone request to be cleaned up
>>>> diff --git a/block/blk-settings.c b/block/blk-settings.c
>>>> index 3c5da75c2def..1895f499bbe5 100644
>>>> --- a/block/blk-settings.c
>>>> +++ b/block/blk-settings.c
>>>> @@ -32,12 +32,6 @@ void blk_queue_rq_timeout(struct request_queue *q, unsigned int timeout)
>>>> }
>>>> EXPORT_SYMBOL_GPL(blk_queue_rq_timeout);
>>>>
>>>> -void blk_queue_lld_busy(struct request_queue *q, lld_busy_fn *fn)
>>>> -{
>>>> - q->lld_busy_fn = fn;
>>>> -}
>>>> -EXPORT_SYMBOL_GPL(blk_queue_lld_busy);
>>>> -
>>>> /**
>>>> * blk_set_default_limits - reset limits to default values
>>>> * @lim: the queue_limits structure to reset
>>>> diff --git a/drivers/md/dm-mpath.c b/drivers/md/dm-mpath.c
>>>> index a24ed3973e7c..4d736e0fd67f 100644
>>>> --- a/drivers/md/dm-mpath.c
>>>> +++ b/drivers/md/dm-mpath.c
>>>> @@ -1936,9 +1936,7 @@ static int multipath_iterate_devices(struct dm_target *ti,
>>>>
>>>> static int pgpath_busy(struct pgpath *pgpath)
>>>> {
>>>> - struct request_queue *q = bdev_get_queue(pgpath->path.dev->bdev);
>>>> -
>>>> - return blk_lld_busy(q);
>>>> + return 0;
>>>> }
>>>>
>>>> /*
>>> Actually, I'm not quite sure this is correct; dm-mpath needs to return a
>>> busy status (via the '->busy' callback) to allow for back-pressure on
>>> the upper layers.
>>> Just disabling the callback will disable this.
>>> Shouldn't we check if the tagmap is busy here?
>>
>> Mike? We can pretty easily make it just check for busy tags.
>
> OK, please feel free to do so.
>
> Happy to pick the patch up or provide review so you can stage it in your
> 4.21 oriented tree.
I reshuffled a bit and made SCSI provide an mq variant of the target
busy. So blk_lld_busy() remains, just with an mq handler instead.
This means that dm-mpath won't need any changing, I think we're good.
--
Jens Axboe
