Re: [PATCH v8] block: cancel all throttled bios in del_gendisk()

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在 2022/02/09 9:39, Ming Lei 写道:
On Tue, Feb 08, 2022 at 07:38:08PM +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.

Signed-off-by: Yu Kuai <yukuai3@xxxxxxxxxx>
---
Changes in v8:
  - fold two patches into one
Changes in v7:
  - use the new solution as suggested by Ming.

  block/blk-throttle.c | 49 ++++++++++++++++++++++++++++++++++++++++----
  block/blk-throttle.h |  2 ++
  block/genhd.c        |  2 ++
  3 files changed, 49 insertions(+), 4 deletions(-)

diff --git a/block/blk-throttle.c b/block/blk-throttle.c
index 7c462c006b26..557d20796157 100644
--- a/block/blk-throttle.c
+++ b/block/blk-throttle.c
@@ -43,8 +43,12 @@
  static struct workqueue_struct *kthrotld_workqueue;
enum tg_state_flags {
-	THROTL_TG_PENDING	= 1 << 0,	/* on parent's pending tree */
-	THROTL_TG_WAS_EMPTY	= 1 << 1,	/* bio_lists[] became non-empty */
+	/* on parent's pending tree */
+	THROTL_TG_PENDING	= 1 << 0,
+	/* bio_lists[] became non-empty */
+	THROTL_TG_WAS_EMPTY	= 1 << 1,
+	/* starts to cancel all bios, will be set if the disk is deleted */
+	THROTL_TG_CANCELING	= 1 << 2,
  };
#define rb_entry_tg(node) rb_entry((node), struct throtl_grp, rb_node)
@@ -871,7 +875,8 @@ static bool tg_may_dispatch(struct throtl_grp *tg, struct bio *bio,
  	       bio != throtl_peek_queued(&tg->service_queue.queued[rw]));
/* If tg->bps = -1, then BW is unlimited */
-	if (bps_limit == U64_MAX && iops_limit == UINT_MAX) {
+	if ((bps_limit == U64_MAX && iops_limit == UINT_MAX) ||
+	    tg->flags & THROTL_TG_CANCELING) {
  		if (wait)
  			*wait = 0;
  		return true;
@@ -974,6 +979,9 @@ static void tg_update_disptime(struct throtl_grp *tg)
  	unsigned long read_wait = -1, write_wait = -1, min_wait = -1, disptime;
  	struct bio *bio;
+ if (tg->flags & THROTL_TG_CANCELING)
+		goto update;
+
  	bio = throtl_peek_queued(&sq->queued[READ]);
  	if (bio)
  		tg_may_dispatch(tg, bio, &read_wait);
@@ -983,9 +991,10 @@ static void tg_update_disptime(struct throtl_grp *tg)
  		tg_may_dispatch(tg, bio, &write_wait);
min_wait = min(read_wait, write_wait);
-	disptime = jiffies + min_wait;
+update:
  	/* Update dispatch time */
+	disptime = jiffies + min_wait;

As I mentioned on V7, the change in tg_update_disptime() isn't needed, please
drop it.

Hi,
After dropping it, disptime will set to jiffies instead of
jiffies -1, this is fine since time_before() won't pass in
throtl_select_dispatch(). I'll drop it in v9...

  	throtl_dequeue_tg(tg);
  	tg->disptime = disptime;
  	throtl_enqueue_tg(tg);
@@ -1763,6 +1772,38 @@ static bool throtl_hierarchy_can_upgrade(struct throtl_grp *tg)
  	return false;
  }
+void blk_throtl_cancel_bios(struct request_queue *q)
+{
+	struct cgroup_subsys_state *pos_css;
+	struct blkcg_gq *blkg;
+
+	spin_lock_irq(&q->queue_lock);
+	/*
+	 * queue_lock is held, rcu lock is not needed here technically.
+	 * However, rcu lock is still held to emphasize that following
+	 * path need RCU protection and to prevent warning from lockdep.
+	 */
+	rcu_read_lock();
+	blkg_for_each_descendant_post(blkg, pos_css, q->root_blkg) {
+		struct throtl_grp *tg = blkg_to_tg(blkg);
+		struct throtl_service_queue *sq = &tg->service_queue;
+
+		/*
+		 * Set disptime in the past to make sure
+		 * throtl_select_dispatch() won't exit without dispatching.
+		 */
+		tg->disptime = jiffies - 1;

It might be better to replace the above line with tg_update_disptime().

Ok, I'll replace it and setting the flag first.

Thanks,
Kuai

Otherwise, the patch looks good.

Thanks,
Ming

.




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