blk-throttle: dispatch to throtl_data->service_queue.bio_lists[]

throtl_service_queues will eventually form a tree which is anchored at
throtl_data->service_queue and queue bios will climb the tree to the
top service_queue to be executed.

This patch makes the dispatch paths in blk_throtl_dispatch_work_fn()
and blk_throtl_drain() to dispatch bios to
throtl_data->service_queue.bio_lists[] instead of the on-stack
bio_lists.  This will keep the final dispatch to the top level
service_queue share the same mechanism as dispatches through the rest
of the hierarchy.

As bio's should be issued in a sleepable context,
blk_throtl_dispatch_work_fn() transfers all dispatched bio's from the
service_queue bio_lists[] into an onstack one before dropping
queue_lock and issuing the bio's.

Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: Vivek Goyal <vgoyal@redhat.com>

1 files changed, 23 insertions, 17 deletions

diff --git a/block/blk-throttle.c b/block/blk-throttle.c
index 6f57f94c3c57..154bd63719c5 100644
--- a/block/blk-throttle.c
+++ b/block/blk-throttle.c
@@ -743,7 +743,7 @@ static void tg_update_disptime(struct throtl_grp *tg,
 }
 
 static void tg_dispatch_one_bio(struct throtl_grp *tg, bool rw,
-                                struct bio_list *bl)
+                                struct throtl_service_queue *parent_sq)
 {
         struct throtl_service_queue *sq = &tg->service_queue;
         struct bio *bio;
@@ -757,13 +757,14 @@ static void tg_dispatch_one_bio(struct throtl_grp *tg, bool rw,
         tg->td->nr_queued[rw]--;
 
         throtl_charge_bio(tg, bio);
-        bio_list_add(bl, bio);
+        bio_list_add(&parent_sq->bio_lists[rw], bio);
         bio->bi_rw |= REQ_THROTTLED;
 
         throtl_trim_slice(tg, rw);
 }
 
-static int throtl_dispatch_tg(struct throtl_grp *tg, struct bio_list *bl)
+static int throtl_dispatch_tg(struct throtl_grp *tg,
+                              struct throtl_service_queue *parent_sq)
 {
         struct throtl_service_queue *sq = &tg->service_queue;
         unsigned int nr_reads = 0, nr_writes = 0;
@@ -776,7 +777,7 @@ static int throtl_dispatch_tg(struct throtl_grp *tg, struct bio_list *bl)
         while ((bio = bio_list_peek(&sq->bio_lists[READ])) &&
                tg_may_dispatch(tg, bio, NULL)) {
 
-                tg_dispatch_one_bio(tg, bio_data_dir(bio), bl);
+                tg_dispatch_one_bio(tg, bio_data_dir(bio), parent_sq);
                 nr_reads++;
 
                 if (nr_reads >= max_nr_reads)
@@ -786,7 +787,7 @@ static int throtl_dispatch_tg(struct throtl_grp *tg, struct bio_list *bl)
         while ((bio = bio_list_peek(&sq->bio_lists[WRITE])) &&
                tg_may_dispatch(tg, bio, NULL)) {
 
-                tg_dispatch_one_bio(tg, bio_data_dir(bio), bl);
+                tg_dispatch_one_bio(tg, bio_data_dir(bio), parent_sq);
                 nr_writes++;
 
                 if (nr_writes >= max_nr_writes)
@@ -796,8 +797,7 @@ static int throtl_dispatch_tg(struct throtl_grp *tg, struct bio_list *bl)
         return nr_reads + nr_writes;
 }
 
-static int throtl_select_dispatch(struct throtl_service_queue *parent_sq,
-                                  struct bio_list *bl)
+static int throtl_select_dispatch(struct throtl_service_queue *parent_sq)
 {
         unsigned int nr_disp = 0;
 
@@ -813,7 +813,7 @@ static int throtl_select_dispatch(struct throtl_service_queue *parent_sq,
 
                 throtl_dequeue_tg(tg, parent_sq);
 
-                nr_disp += throtl_dispatch_tg(tg, bl);
+                nr_disp += throtl_dispatch_tg(tg, parent_sq);
 
                 if (sq->nr_queued[0] || sq->nr_queued[1])
                         tg_update_disptime(tg, parent_sq);
@@ -830,11 +830,13 @@ void blk_throtl_dispatch_work_fn(struct work_struct *work)
 {
         struct throtl_data *td = container_of(to_delayed_work(work),
                                               struct throtl_data, dispatch_work);
+        struct throtl_service_queue *sq = &td->service_queue;
         struct request_queue *q = td->queue;
         unsigned int nr_disp = 0;
         struct bio_list bio_list_on_stack;
         struct bio *bio;
         struct blk_plug plug;
+        int rw;
 
         spin_lock_irq(q->queue_lock);
 
@@ -844,10 +846,15 @@ void blk_throtl_dispatch_work_fn(struct work_struct *work)
                    td->nr_queued[READ] + td->nr_queued[WRITE],
                    td->nr_queued[READ], td->nr_queued[WRITE]);
 
-        nr_disp = throtl_select_dispatch(&td->service_queue, &bio_list_on_stack);
+        nr_disp = throtl_select_dispatch(sq);
 
-        if (nr_disp)
+        if (nr_disp) {
+                for (rw = READ; rw <= WRITE; rw++) {
+                        bio_list_merge(&bio_list_on_stack, &sq->bio_lists[rw]);
+                        bio_list_init(&sq->bio_lists[rw]);
+                }
                 throtl_log(td, "bios disp=%u", nr_disp);
+        }
 
         throtl_schedule_next_dispatch(td);
 
@@ -1156,27 +1163,26 @@ void blk_throtl_drain(struct request_queue *q)
         struct throtl_data *td = q->td;
         struct throtl_service_queue *parent_sq = &td->service_queue;
         struct throtl_grp *tg;
-        struct bio_list bl;
         struct bio *bio;
+        int rw;
 
         queue_lockdep_assert_held(q);
 
-        bio_list_init(&bl);
-
         while ((tg = throtl_rb_first(parent_sq))) {
                 struct throtl_service_queue *sq = &tg->service_queue;
 
                 throtl_dequeue_tg(tg, parent_sq);
 
                 while ((bio = bio_list_peek(&sq->bio_lists[READ])))
-                        tg_dispatch_one_bio(tg, bio_data_dir(bio), &bl);
+                        tg_dispatch_one_bio(tg, bio_data_dir(bio), parent_sq);
                 while ((bio = bio_list_peek(&sq->bio_lists[WRITE])))
-                        tg_dispatch_one_bio(tg, bio_data_dir(bio), &bl);
+                        tg_dispatch_one_bio(tg, bio_data_dir(bio), parent_sq);
         }
         spin_unlock_irq(q->queue_lock);
 
-        while ((bio = bio_list_pop(&bl)))
-                generic_make_request(bio);
+        for (rw = READ; rw <= WRITE; rw++)
+                while ((bio = bio_list_pop(&parent_sq->bio_lists[rw])))
+                        generic_make_request(bio);
 
         spin_lock_irq(q->queue_lock);
 }