Re: [PATCH 28/51] writeback, blkcg: restructure blk_{set|clear}_queue_congested()

[Jan Kara]

On Fri 22-05-15 17:13:42, Tejun Heo wrote:
> blk_{set|clear}_queue_congested() take @q and set or clear,
> respectively, the congestion state of its bdi's root wb.  Because bdi
> used to be able to handle congestion state only on the root wb, the
> callers of those functions tested whether the congestion is on the
> root blkcg and skipped if not.
> 
> This is cumbersome and makes implementation of per cgroup
> bdi_writeback congestion state propagation difficult.  This patch
> renames blk_{set|clear}_queue_congested() to
> blk_{set|clear}_congested(), and makes them take request_list instead
> of request_queue and test whether the specified request_list is the
> root one before updating bdi_writeback congestion state.  This makes
> the tests in the callers unnecessary and simplifies them.
> 
> As there are no external users of these functions, the definitions are
> moved from include/linux/blkdev.h to block/blk-core.c.
> 
> This patch doesn't introduce any noticeable behavior difference.

Looks good. You can add:

Reviewed-by: Jan Kara <jack@xxxxxxxx>

BTW, I'd prefer if this was merged with the following patch. I was
wondering for a while about the condition at the beginning of
blk_clear_congested() only to learn it gets modified to the one I'd expect
in the following patch :)

								Honza

> 
> Signed-off-by: Tejun Heo <tj@xxxxxxxxxx>
> Cc: Jens Axboe <axboe@xxxxxxxxx>
> Cc: Jan Kara <jack@xxxxxxx>
> Cc: Vivek Goyal <vgoyal@xxxxxxxxxx>
> ---
>  block/blk-core.c       | 62 ++++++++++++++++++++++++++++++--------------------
>  include/linux/blkdev.h | 19 ----------------
>  2 files changed, 37 insertions(+), 44 deletions(-)
> 
> diff --git a/block/blk-core.c b/block/blk-core.c
> index e0f726f..b457c4f 100644
> --- a/block/blk-core.c
> +++ b/block/blk-core.c
> @@ -63,6 +63,28 @@ struct kmem_cache *blk_requestq_cachep;
>   */
>  static struct workqueue_struct *kblockd_workqueue;
>  
> +static void blk_clear_congested(struct request_list *rl, int sync)
> +{
> +	if (rl != &rl->q->root_rl)
> +		return;
> +#ifdef CONFIG_CGROUP_WRITEBACK
> +	clear_wb_congested(rl->blkg->wb_congested, sync);
> +#else
> +	clear_wb_congested(rl->q->backing_dev_info.wb.congested, sync);
> +#endif
> +}
> +
> +static void blk_set_congested(struct request_list *rl, int sync)
> +{
> +	if (rl != &rl->q->root_rl)
> +		return;
> +#ifdef CONFIG_CGROUP_WRITEBACK
> +	set_wb_congested(rl->blkg->wb_congested, sync);
> +#else
> +	set_wb_congested(rl->q->backing_dev_info.wb.congested, sync);
> +#endif
> +}
> +
>  void blk_queue_congestion_threshold(struct request_queue *q)
>  {
>  	int nr;
> @@ -841,13 +863,8 @@ static void __freed_request(struct request_list *rl, int sync)
>  {
>  	struct request_queue *q = rl->q;
>  
> -	/*
> -	 * bdi isn't aware of blkcg yet.  As all async IOs end up root
> -	 * blkcg anyway, just use root blkcg state.
> -	 */
> -	if (rl == &q->root_rl &&
> -	    rl->count[sync] < queue_congestion_off_threshold(q))
> -		blk_clear_queue_congested(q, sync);
> +	if (rl->count[sync] < queue_congestion_off_threshold(q))
> +		blk_clear_congested(rl, sync);
>  
>  	if (rl->count[sync] + 1 <= q->nr_requests) {
>  		if (waitqueue_active(&rl->wait[sync]))
> @@ -880,25 +897,25 @@ static void freed_request(struct request_list *rl, unsigned int flags)
>  int blk_update_nr_requests(struct request_queue *q, unsigned int nr)
>  {
>  	struct request_list *rl;
> +	int on_thresh, off_thresh;
>  
>  	spin_lock_irq(q->queue_lock);
>  	q->nr_requests = nr;
>  	blk_queue_congestion_threshold(q);
> +	on_thresh = queue_congestion_on_threshold(q);
> +	off_thresh = queue_congestion_off_threshold(q);
>  
> -	/* congestion isn't cgroup aware and follows root blkcg for now */
> -	rl = &q->root_rl;
> -
> -	if (rl->count[BLK_RW_SYNC] >= queue_congestion_on_threshold(q))
> -		blk_set_queue_congested(q, BLK_RW_SYNC);
> -	else if (rl->count[BLK_RW_SYNC] < queue_congestion_off_threshold(q))
> -		blk_clear_queue_congested(q, BLK_RW_SYNC);
> +	blk_queue_for_each_rl(rl, q) {
> +		if (rl->count[BLK_RW_SYNC] >= on_thresh)
> +			blk_set_congested(rl, BLK_RW_SYNC);
> +		else if (rl->count[BLK_RW_SYNC] < off_thresh)
> +			blk_clear_congested(rl, BLK_RW_SYNC);
>  
> -	if (rl->count[BLK_RW_ASYNC] >= queue_congestion_on_threshold(q))
> -		blk_set_queue_congested(q, BLK_RW_ASYNC);
> -	else if (rl->count[BLK_RW_ASYNC] < queue_congestion_off_threshold(q))
> -		blk_clear_queue_congested(q, BLK_RW_ASYNC);
> +		if (rl->count[BLK_RW_ASYNC] >= on_thresh)
> +			blk_set_congested(rl, BLK_RW_ASYNC);
> +		else if (rl->count[BLK_RW_ASYNC] < off_thresh)
> +			blk_clear_congested(rl, BLK_RW_ASYNC);
>  
> -	blk_queue_for_each_rl(rl, q) {
>  		if (rl->count[BLK_RW_SYNC] >= q->nr_requests) {
>  			blk_set_rl_full(rl, BLK_RW_SYNC);
>  		} else {
> @@ -1008,12 +1025,7 @@ static struct request *__get_request(struct request_list *rl, int rw_flags,
>  				}
>  			}
>  		}
> -		/*
> -		 * bdi isn't aware of blkcg yet.  As all async IOs end up
> -		 * root blkcg anyway, just use root blkcg state.
> -		 */
> -		if (rl == &q->root_rl)
> -			blk_set_queue_congested(q, is_sync);
> +		blk_set_congested(rl, is_sync);
>  	}
>  
>  	/*
> diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
> index 89bdef0..3d1065c 100644
> --- a/include/linux/blkdev.h
> +++ b/include/linux/blkdev.h
> @@ -794,25 +794,6 @@ extern int sg_scsi_ioctl(struct request_queue *, struct gendisk *, fmode_t,
>  
>  extern void blk_queue_bio(struct request_queue *q, struct bio *bio);
>  
> -/*
> - * A queue has just exitted congestion.  Note this in the global counter of
> - * congested queues, and wake up anyone who was waiting for requests to be
> - * put back.
> - */
> -static inline void blk_clear_queue_congested(struct request_queue *q, int sync)
> -{
> -	clear_bdi_congested(&q->backing_dev_info, sync);
> -}
> -
> -/*
> - * A queue has just entered congestion.  Flag that in the queue's VM-visible
> - * state flags and increment the global gounter of congested queues.
> - */
> -static inline void blk_set_queue_congested(struct request_queue *q, int sync)
> -{
> -	set_bdi_congested(&q->backing_dev_info, sync);
> -}
> -
>  extern void blk_start_queue(struct request_queue *q);
>  extern void blk_stop_queue(struct request_queue *q);
>  extern void blk_sync_queue(struct request_queue *q);
> -- 
> 2.4.0
> 
-- 
Jan Kara <jack@xxxxxxx>
SUSE Labs, CR
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