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

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

 



On Fri, Jan 14, 2022 at 04:21:04PM +0800, yukuai (C) wrote:
> 在 2022/01/14 11:05, Ming Lei 写道:
> > On Thu, Jan 13, 2022 at 04:46:18PM +0800, yukuai (C) wrote:
> > > 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@xxxxxxxxxx>
> > > > > ---
> > > > >    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?
> > 
> > I thought that throttled bios will be canceled by 'tg->disptime = jiffies - 1;'
> > and the following dispatch schedule.
> > 
> > But looks it isn't enough, since tg_update_disptime() updates
> > ->disptime. However,
> > this problem can be solved easily by not updating ->disptime in case that we are
> > canceling.
> > 
> > > >      }
> > > > -   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.
> > 
> > Firstly ->queue_lock is held by blk_throtl_cancel_bios(), so no new bios
> > will be throttled.
> > 
> > Also if we don't update ->disptime, any new bios throttled after releasing
> > ->queue_lock will be dispatched soon.
> 
> Hi, Ming Lei
> 
> Just to be curiosity, I'm still trying to understand the logic here:
> 
> For example, if bps is set to 1k, and a io with size 16k is just
> dispatched, then io throtle should wait for 16s untill new io can be

There isn't such wait code in blk-throttle, and the magic is just in
how to compute tg->disptime.

> dispatched. (details in tg_with_in_bps_limit).
> 
> How does such mechanism bypassed here?

The point is that tg->disptime is always set as one past time, so all
throttled IOs will be dispatched immediately if ->disptime is older than
jiffies, and I have verified that the following patch can work as expected.


diff --git a/block/blk-throttle.c b/block/blk-throttle.c
index 7c462c006b26..d9845afccd97 100644
--- a/block/blk-throttle.c
+++ b/block/blk-throttle.c
@@ -45,6 +45,7 @@ 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 */
+	THROTL_TG_CANCELING	= 1 << 2,	/* starts to cancel all bios */
 };
 
 #define rb_entry_tg(node)	rb_entry((node), struct throtl_grp, rb_node)
@@ -974,6 +975,9 @@ 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);
@@ -983,6 +987,7 @@ static void tg_update_disptime(struct throtl_grp *tg)
 		tg_may_dispatch(tg, bio, &write_wait);
 
 	min_wait = min(read_wait, write_wait);
+update:
 	disptime = jiffies + min_wait;
 
 	/* Update dispatch time */
@@ -1836,6 +1841,25 @@ static void throtl_upgrade_state(struct throtl_data *td)
 	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);
+	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;
+
+		tg->disptime = jiffies - 1;
+		blkg_to_tg(blkg)->flags |= THROTL_TG_CANCELING;
+		throtl_schedule_pending_timer(sq, jiffies + 1);
+	}
+	spin_unlock_irq(&q->queue_lock);
+	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 175f03abd9e4..b412a4d7cc1e 100644
--- a/block/blk-throttle.h
+++ b/block/blk-throttle.h
@@ -160,12 +160,14 @@ static inline void blk_throtl_exit(struct request_queue *q) { }
 static inline void blk_throtl_register_queue(struct request_queue *q) { }
 static inline void blk_throtl_charge_bio_split(struct bio *bio) { }
 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);
 void blk_throtl_charge_bio_split(struct bio *bio);
 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 f7577dde18fc..a32d48b87223 100644
--- a/block/genhd.c
+++ b/block/genhd.c
@@ -29,6 +29,7 @@
 
 #include "blk.h"
 #include "blk-mq-sched.h"
+#include "blk-throttle.h"
 
 static struct kobject *block_depr;
 
@@ -576,6 +577,8 @@ void del_gendisk(struct gendisk *disk)
 	blk_integrity_del(disk);
 	disk_del_events(disk);
 
+	blk_throtl_cancel_bios(disk->queue);
+
 	mutex_lock(&disk->open_mutex);
 	remove_inode_hash(disk->part0->bd_inode);
 	blk_drop_partitions(disk);

Thanks,
Ming




[Index of Archives]     [Linux RAID]     [Linux SCSI]     [Linux ATA RAID]     [IDE]     [Linux Wireless]     [Linux Kernel]     [ATH6KL]     [Linux Bluetooth]     [Linux Netdev]     [Kernel Newbies]     [Security]     [Git]     [Netfilter]     [Bugtraq]     [Yosemite News]     [MIPS Linux]     [ARM Linux]     [Linux Security]     [Device Mapper]

  Powered by Linux