blkcg: move per-queue blkg list heads and counters to queue and blkg

Currently, specific policy implementations are responsible for
maintaining list and number of blkgs.  This duplicates code
unnecessarily, and hinders factoring common code and providing blkcg
API with better defined semantics.

After this patch, request_queue hosts list heads and counters and blkg
has list nodes for both policies.  This patch only relocates the
necessary fields and the next patch will actually move management code
into blkcg core.

Note that request_queue->blkg_list[] and ->nr_blkgs[] are hardcoded to
have 2 elements.  This is to avoid include dependency and will be
removed by the next patch.

This patch doesn't introduce any behavior change.

-v2: Now unnecessary conditional on CONFIG_BLK_CGROUP_MODULE removed
     as pointed out by Vivek.

Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: Vivek Goyal <vgoyal@redhat.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

1 files changed, 23 insertions, 26 deletions

diff --git a/block/blk-throttle.c b/block/blk-throttle.c
index b2fddaf20b98..c15d38307e1d 100644
--- a/block/blk-throttle.c
+++ b/block/blk-throttle.c
@@ -41,9 +41,6 @@ struct throtl_rb_root {
 #define rb_entry_tg(node)       rb_entry((node), struct throtl_grp, rb_node)
 
 struct throtl_grp {
-        /* List of throtl groups on the request queue*/
-        struct hlist_node tg_node;
-
         /* active throtl group service_tree member */
         struct rb_node rb_node;
 
@@ -83,9 +80,6 @@ struct throtl_grp {
 
 struct throtl_data
 {
-        /* List of throtl groups */
-        struct hlist_head tg_list;
-
         /* service tree for active throtl groups */
         struct throtl_rb_root tg_service_tree;
 
@@ -152,7 +146,6 @@ static void throtl_init_blkio_group(struct blkio_group *blkg)
 {
         struct throtl_grp *tg = blkg_to_tg(blkg);
 
-        INIT_HLIST_NODE(&tg->tg_node);
         RB_CLEAR_NODE(&tg->rb_node);
         bio_list_init(&tg->bio_lists[0]);
         bio_list_init(&tg->bio_lists[1]);
@@ -167,11 +160,9 @@ static void throtl_init_blkio_group(struct blkio_group *blkg)
 static void throtl_link_blkio_group(struct request_queue *q,
                                     struct blkio_group *blkg)
 {
-        struct throtl_data *td = q->td;
-        struct throtl_grp *tg = blkg_to_tg(blkg);
-
-        hlist_add_head(&tg->tg_node, &td->tg_list);
-        td->nr_undestroyed_grps++;
+        list_add(&blkg->q_node[BLKIO_POLICY_THROTL],
+                 &q->blkg_list[BLKIO_POLICY_THROTL]);
+        q->nr_blkgs[BLKIO_POLICY_THROTL]++;
 }
 
 static struct
@@ -711,8 +702,8 @@ static int throtl_select_dispatch(struct throtl_data *td, struct bio_list *bl)
 
 static void throtl_process_limit_change(struct throtl_data *td)
 {
-        struct throtl_grp *tg;
-        struct hlist_node *pos, *n;
+        struct request_queue *q = td->queue;
+        struct blkio_group *blkg, *n;
 
         if (!td->limits_changed)
                 return;
@@ -721,7 +712,10 @@ static void throtl_process_limit_change(struct throtl_data *td)
 
         throtl_log(td, "limits changed");
 
-        hlist_for_each_entry_safe(tg, pos, n, &td->tg_list, tg_node) {
+        list_for_each_entry_safe(blkg, n, &q->blkg_list[BLKIO_POLICY_THROTL],
+                                 q_node[BLKIO_POLICY_THROTL]) {
+                struct throtl_grp *tg = blkg_to_tg(blkg);
+
                 if (!tg->limits_changed)
                         continue;
 
@@ -822,26 +816,31 @@ throtl_schedule_delayed_work(struct throtl_data *td, unsigned long delay)
 static void
 throtl_destroy_tg(struct throtl_data *td, struct throtl_grp *tg)
 {
+        struct blkio_group *blkg = tg_to_blkg(tg);
+
         /* Something wrong if we are trying to remove same group twice */
-        BUG_ON(hlist_unhashed(&tg->tg_node));
+        WARN_ON_ONCE(list_empty(&blkg->q_node[BLKIO_POLICY_THROTL]));
 
-        hlist_del_init(&tg->tg_node);
+        list_del_init(&blkg->q_node[BLKIO_POLICY_THROTL]);
 
         /*
          * Put the reference taken at the time of creation so that when all
          * queues are gone, group can be destroyed.
          */
         blkg_put(tg_to_blkg(tg));
-        td->nr_undestroyed_grps--;
+        td->queue->nr_blkgs[BLKIO_POLICY_THROTL]--;
 }
 
 static bool throtl_release_tgs(struct throtl_data *td, bool release_root)
 {
-        struct hlist_node *pos, *n;
-        struct throtl_grp *tg;
+        struct request_queue *q = td->queue;
+        struct blkio_group *blkg, *n;
         bool empty = true;
 
-        hlist_for_each_entry_safe(tg, pos, n, &td->tg_list, tg_node) {
+        list_for_each_entry_safe(blkg, n, &q->blkg_list[BLKIO_POLICY_THROTL],
+                                 q_node[BLKIO_POLICY_THROTL]) {
+                struct throtl_grp *tg = blkg_to_tg(blkg);
+
                 /* skip root? */
                 if (!release_root && tg == td->root_tg)
                         continue;
@@ -851,7 +850,7 @@ static bool throtl_release_tgs(struct throtl_data *td, bool release_root)
                  * it from cgroup list, then it will take care of destroying
                  * cfqg also.
                  */
-                if (!blkiocg_del_blkio_group(tg_to_blkg(tg)))
+                if (!blkiocg_del_blkio_group(blkg))
                         throtl_destroy_tg(td, tg);
                 else
                         empty = false;
@@ -1114,7 +1113,6 @@ int blk_throtl_init(struct request_queue *q)
         if (!td)
                 return -ENOMEM;
 
-        INIT_HLIST_HEAD(&td->tg_list);
         td->tg_service_tree = THROTL_RB_ROOT;
         td->limits_changed = false;
         INIT_DELAYED_WORK(&td->throtl_work, blk_throtl_work);
@@ -1144,7 +1142,7 @@ int blk_throtl_init(struct request_queue *q)
 void blk_throtl_exit(struct request_queue *q)
 {
         struct throtl_data *td = q->td;
-        bool wait = false;
+        bool wait;
 
         BUG_ON(!td);
 
@@ -1154,8 +1152,7 @@ void blk_throtl_exit(struct request_queue *q)
         throtl_release_tgs(td, true);
 
         /* If there are other groups */
-        if (td->nr_undestroyed_grps > 0)
-                wait = true;
+        wait = q->nr_blkgs[BLKIO_POLICY_THROTL];
 
         spin_unlock_irq(q->queue_lock);