Re: [PATCH v6 2/2] block: cancel all throttled bios in del_gendisk()

yukuai (C)
2022-01-13T08:46:26Z

在 2022/01/12 11:05, Ming Lei 写道:
> Hello Yu Kuai,
>
> On Mon, Jan 10, 2022 at 09:47:58PM +0800, Yu Kuai wrote:
>> Throttled bios can't be issued after del_gendisk() is done, thus
>> it's better to cancel them immediately rather than waiting for
>> throttle is done.
>>
>> For example, if user thread is throttled with low bps while it's
>> issuing large io, and the device is deleted. The user thread will
>> wait for a long time for io to return.
>>
>> Noted this patch is mainly from revertion of commit 32e3374304c7
>> ("blk-throttle: remove tg_drain_bios") and commit b77412372b68
>> ("blk-throttle: remove blk_throtl_drain").
>>
>> Signed-off-by: Yu Kuai <yukuai3@huawei.com>
>> ---
>> block/blk-throttle.c | 77 ++++++++++++++++++++++++++++++++++++++++++++
>> block/blk-throttle.h | 2 ++
>> block/genhd.c | 2 ++
>> 3 files changed, 81 insertions(+)
>
> Just wondering why not take the built-in way in throtl_upgrade_state() for
> canceling throttled bios? Something like the following, then we can avoid
> to re-invent the wheel.
>
> block/blk-throttle.c | 38 +++++++++++++++++++++++++++++++-------
> block/blk-throttle.h | 2 ++
> block/genhd.c | 3 +++
> 3 files changed, 36 insertions(+), 7 deletions(-)
>
> diff --git a/block/blk-throttle.c b/block/blk-throttle.c
> index cf7e20804f1b..17e56b2e44c4 100644
> --- a/block/blk-throttle.c
> +++ b/block/blk-throttle.c
> @@ -1816,16 +1816,11 @@ static void throtl_upgrade_check(struct throtl_grp *tg)
> throtl_upgrade_state(tg->td);
> }
>
> -static void throtl_upgrade_state(struct throtl_data *td)
> +static void __throtl_cancel_bios(struct throtl_data *td)
> {
> struct cgroup_subsys_state *pos_css;
> struct blkcg_gq *blkg;
>
> - throtl_log(&td->service_queue, "upgrade to max");
> - td->limit_index = LIMIT_MAX;
> - td->low_upgrade_time = jiffies;
> - td->scale = 0;
> - rcu_read_lock();
> blkg_for_each_descendant_post(blkg, pos_css, td->queue->root_blkg) {
> struct throtl_grp *tg = blkg_to_tg(blkg);
> struct throtl_service_queue *sq = &tg->service_queue;
> @@ -1834,12 +1829,41 @@ static void throtl_upgrade_state(struct throtl_data *td)
> throtl_select_dispatch(sq);
> throtl_schedule_next_dispatch(sq, true);
Hi, Ming Lei

I'm confused that how can bios be canceled here?
tg->iops and tg->bps stay untouched, how can throttled bios
dispatch?
> }
> - rcu_read_unlock();
> throtl_select_dispatch(&td->service_queue);
> throtl_schedule_next_dispatch(&td->service_queue, true);
> queue_work(kthrotld_workqueue, &td->dispatch_work);
> }
>
> +void blk_throtl_cancel_bios(struct request_queue *q)
> +{
> + struct cgroup_subsys_state *pos_css;
> + struct blkcg_gq *blkg;
> +
> + rcu_read_lock();
> + spin_lock_irq(&q->queue_lock);
> + __throtl_cancel_bios(q->td);
> + spin_unlock_irq(&q->queue_lock);
> + rcu_read_unlock();
> +
> + blkg_for_each_descendant_post(blkg, pos_css, q->root_blkg)
> + del_timer_sync(&blkg_to_tg(blkg)->service_queue.pending_timer);
> + del_timer_sync(&q->td->service_queue.pending_timer);

By the way, I think delete timer will end up io hung here if there are
some bios still be throttled.

Thanks,
Kuai
> +
> + throtl_shutdown_wq(q);
> +}
> +
> +static void throtl_upgrade_state(struct throtl_data *td)
> +{
> + throtl_log(&td->service_queue, "upgrade to max");
> + td->limit_index = LIMIT_MAX;
> + td->low_upgrade_time = jiffies;
> + td->scale = 0;
> +
> + rcu_read_lock();
> + __throtl_cancel_bios(td);
> + rcu_read_unlock();
> +}
> +
> static void throtl_downgrade_state(struct throtl_data *td)
> {
> td->scale /= 2;
> diff --git a/block/blk-throttle.h b/block/blk-throttle.h
> index b23a9f3abb82..525ac607c518 100644
> --- a/block/blk-throttle.h
> +++ b/block/blk-throttle.h
> @@ -162,11 +162,13 @@ static inline int blk_throtl_init(struct request_queue *q) { return 0; }
> static inline void blk_throtl_exit(struct request_queue *q) { }
> static inline void blk_throtl_register_queue(struct request_queue *q) { }
> static inline bool blk_throtl_bio(struct bio *bio) { return false; }
> +static inline void blk_throtl_cancel_bios(struct request_queue *q) {}
> #else /* CONFIG_BLK_DEV_THROTTLING */
> int blk_throtl_init(struct request_queue *q);
> void blk_throtl_exit(struct request_queue *q);
> void blk_throtl_register_queue(struct request_queue *q);
> bool __blk_throtl_bio(struct bio *bio);
> +void blk_throtl_cancel_bios(struct request_queue *q);
> static inline bool blk_throtl_bio(struct bio *bio)
> {
> struct throtl_grp *tg = blkg_to_tg(bio->bi_blkg);
> diff --git a/block/genhd.c b/block/genhd.c
> index 626c8406f21a..1395cbd8eacf 100644
> --- a/block/genhd.c
> +++ b/block/genhd.c
> @@ -30,6 +30,7 @@
> #include "blk.h"
> #include "blk-mq-sched.h"
> #include "blk-rq-qos.h"
> +#include "blk-throttle.h"
>
> static struct kobject *block_depr;
>
> @@ -622,6 +623,8 @@ void del_gendisk(struct gendisk *disk)
>
> blk_mq_freeze_queue_wait(q);
>
> + blk_throtl_cancel_bios(q);
> +
> rq_qos_exit(q);
> blk_sync_queue(q);
> blk_flush_integrity();
>
> Thanks,
> Ming
>
> .
>