blkcg: use the usual get blkg path for root blkio_group

For root blkg, blk_throtl_init() was using throtl_alloc_tg()
explicitly and cfq_init_queue() was manually initializing embedded
cfqd->root_group, adding unnecessarily different code paths to blkg
handling.

Make both use the usual blkio_group get functions - throtl_get_tg()
and cfq_get_cfqg() - for the root blkio_group too.  Note that
blk_throtl_init() callsite is pushed downwards in
blk_alloc_queue_node() so that @q is sufficiently initialized for
throtl_get_tg().

This simplifies root blkg handling noticeably for cfq and will allow
further modularization of blkcg API.

-v2: Vivek pointed out that using cfq_get_cfqg() won't work if
     CONFIG_CFQ_GROUP_IOSCHED is disabled.  Fix it by factoring out
     initialization of base part of cfqg into cfq_init_cfqg_base() and
     alloc/init/free explicitly if !CONFIG_CFQ_GROUP_IOSCHED.

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

diff --git a/block/blk-core.c b/block/blk-core.c
index 7713c73..5a1b8cc 100644 (file)
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -540,9 +540,6 @@ struct request_queue *blk_alloc_queue_node(gfp_t gfp_mask, int node_id)
        if (err)
                goto fail_id;
 
-       if (blk_throtl_init(q))
-               goto fail_id;
-
        setup_timer(&q->backing_dev_info.laptop_mode_wb_timer,
                    laptop_mode_timer_fn, (unsigned long) q);
        setup_timer(&q->timeout, blk_rq_timed_out_timer, (unsigned long) q);
@@ -565,6 +562,9 @@ struct request_queue *blk_alloc_queue_node(gfp_t gfp_mask, int node_id)
         */
        q->queue_lock = &q->__queue_lock;
 
+       if (blk_throtl_init(q))
+               goto fail_id;
+
        return q;
 
 fail_id:

diff --git a/block/blk-throttle.c b/block/blk-throttle.c
index 6613de7..aeeb798 100644 (file)
--- a/block/blk-throttle.c
+++ b/block/blk-throttle.c
@@ -1252,7 +1252,6 @@ void blk_throtl_drain(struct request_queue *q)
 int blk_throtl_init(struct request_queue *q)
 {
        struct throtl_data *td;
-       struct throtl_grp *tg;
 
        td = kzalloc_node(sizeof(*td), GFP_KERNEL, q->node);
        if (!td)
@@ -1265,19 +1264,20 @@ int blk_throtl_init(struct request_queue *q)
 
        /* alloc and Init root group. */
        td->queue = q;
-       tg = throtl_alloc_tg(td);
 
-       if (!tg) {
-               kfree(td);
-               return -ENOMEM;
-       }
+       rcu_read_lock();
+       spin_lock_irq(q->queue_lock);
 
-       td->root_tg = tg;
+       td->root_tg = throtl_get_tg(td, &blkio_root_cgroup);
 
-       rcu_read_lock();
-       throtl_init_add_tg_lists(td, tg, &blkio_root_cgroup);
+       spin_unlock_irq(q->queue_lock);
        rcu_read_unlock();
 
+       if (!td->root_tg) {
+               kfree(td);
+               return -ENOMEM;
+       }
+
        /* Attach throtl data to request queue */
        q->td = td;
        return 0;

diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c
index 37e2da9..1c3f41b 100644 (file)
--- a/block/cfq-iosched.c
+++ b/block/cfq-iosched.c
@@ -229,7 +229,7 @@ struct cfq_data {
        struct request_queue *queue;
        /* Root service tree for cfq_groups */
        struct cfq_rb_root grp_service_tree;
-       struct cfq_group root_group;
+       struct cfq_group *root_group;
 
        /*
         * The priority currently being served
@@ -1012,6 +1012,25 @@ static void cfq_group_served(struct cfq_data *cfqd, struct cfq_group *cfqg,
        cfq_blkiocg_set_start_empty_time(&cfqg->blkg);
 }
 
+/**
+ * cfq_init_cfqg_base - initialize base part of a cfq_group
+ * @cfqg: cfq_group to initialize
+ *
+ * Initialize the base part which is used whether %CONFIG_CFQ_GROUP_IOSCHED
+ * is enabled or not.
+ */
+static void cfq_init_cfqg_base(struct cfq_group *cfqg)
+{
+       struct cfq_rb_root *st;
+       int i, j;
+
+       for_each_cfqg_st(cfqg, i, j, st)
+               *st = CFQ_RB_ROOT;
+       RB_CLEAR_NODE(&cfqg->rb_node);
+
+       cfqg->ttime.last_end_request = jiffies;
+}
+
 #ifdef CONFIG_CFQ_GROUP_IOSCHED
 static inline struct cfq_group *cfqg_of_blkg(struct blkio_group *blkg)
 {
@@ -1063,19 +1082,14 @@ static void cfq_init_add_cfqg_lists(struct cfq_data *cfqd,
  */
 static struct cfq_group * cfq_alloc_cfqg(struct cfq_data *cfqd)
 {
-       struct cfq_group *cfqg = NULL;
-       int i, j, ret;
-       struct cfq_rb_root *st;
+       struct cfq_group *cfqg;
+       int ret;
 
        cfqg = kzalloc_node(sizeof(*cfqg), GFP_ATOMIC, cfqd->queue->node);
        if (!cfqg)
                return NULL;
 
-       for_each_cfqg_st(cfqg, i, j, st)
-               *st = CFQ_RB_ROOT;
-       RB_CLEAR_NODE(&cfqg->rb_node);
-
-       cfqg->ttime.last_end_request = jiffies;
+       cfq_init_cfqg_base(cfqg);
 
        /*
         * Take the initial reference that will be released on destroy
@@ -1106,7 +1120,7 @@ cfq_find_cfqg(struct cfq_data *cfqd, struct blkio_cgroup *blkcg)
         * Avoid lookup in this case
         */
        if (blkcg == &blkio_root_cgroup)
-               cfqg = &cfqd->root_group;
+               cfqg = cfqd->root_group;
        else
                cfqg = cfqg_of_blkg(blkiocg_lookup_group(blkcg, cfqd->queue,
                                                         BLKIO_POLICY_PROP));
@@ -1166,7 +1180,7 @@ static struct cfq_group *cfq_get_cfqg(struct cfq_data *cfqd,
        }
 
        if (!cfqg)
-               cfqg = &cfqd->root_group;
+               cfqg = cfqd->root_group;
 
        cfq_init_add_cfqg_lists(cfqd, cfqg, blkcg);
        return cfqg;
@@ -1182,7 +1196,7 @@ static void cfq_link_cfqq_cfqg(struct cfq_queue *cfqq, struct cfq_group *cfqg)
 {
        /* Currently, all async queues are mapped to root group */
        if (!cfq_cfqq_sync(cfqq))
-               cfqg = &cfqq->cfqd->root_group;
+               cfqg = cfqq->cfqd->root_group;
 
        cfqq->cfqg = cfqg;
        /* cfqq reference on cfqg */
@@ -1283,7 +1297,7 @@ static bool cfq_clear_queue(struct request_queue *q)
 static struct cfq_group *cfq_get_cfqg(struct cfq_data *cfqd,
                                      struct blkio_cgroup *blkcg)
 {
-       return &cfqd->root_group;
+       return cfqd->root_group;
 }
 
 static inline struct cfq_group *cfq_ref_get_cfqg(struct cfq_group *cfqg)
@@ -3671,9 +3685,8 @@ static void cfq_exit_queue(struct elevator_queue *e)
        if (wait)
                synchronize_rcu();
 
-#ifdef CONFIG_CFQ_GROUP_IOSCHED
-       /* Free up per cpu stats for root group */
-       free_percpu(cfqd->root_group.blkg.stats_cpu);
+#ifndef CONFIG_CFQ_GROUP_IOSCHED
+       kfree(cfqd->root_group);
 #endif
        kfree(cfqd);
 }
@@ -3681,52 +3694,40 @@ static void cfq_exit_queue(struct elevator_queue *e)
 static int cfq_init_queue(struct request_queue *q)
 {
        struct cfq_data *cfqd;
-       int i, j;
-       struct cfq_group *cfqg;
-       struct cfq_rb_root *st;
+       int i;
 
        cfqd = kmalloc_node(sizeof(*cfqd), GFP_KERNEL | __GFP_ZERO, q->node);
        if (!cfqd)
                return -ENOMEM;
 
+       cfqd->queue = q;
+       q->elevator->elevator_data = cfqd;
+
        /* Init root service tree */
        cfqd->grp_service_tree = CFQ_RB_ROOT;
 
-       /* Init root group */
-       cfqg = &cfqd->root_group;
-       for_each_cfqg_st(cfqg, i, j, st)
-               *st = CFQ_RB_ROOT;
-       RB_CLEAR_NODE(&cfqg->rb_node);
-
-       /* Give preference to root group over other groups */
-       cfqg->weight = 2*BLKIO_WEIGHT_DEFAULT;
-
+       /* Init root group and prefer root group over other groups by default */
 #ifdef CONFIG_CFQ_GROUP_IOSCHED
-       /*
-        * Set root group reference to 2. One reference will be dropped when
-        * all groups on cfqd->cfqg_list are being deleted during queue exit.
-        * Other reference will remain there as we don't want to delete this
-        * group as it is statically allocated and gets destroyed when
-        * throtl_data goes away.
-        */
-       cfqg->ref = 2;
+       rcu_read_lock();
+       spin_lock_irq(q->queue_lock);
 
-       if (blkio_alloc_blkg_stats(&cfqg->blkg)) {
-               kfree(cfqg);
+       cfqd->root_group = cfq_get_cfqg(cfqd, &blkio_root_cgroup);
+
+       spin_unlock_irq(q->queue_lock);
+       rcu_read_unlock();
+#else
+       cfqd->root_group = kzalloc_node(sizeof(*cfqd->root_group),
+                                       GFP_KERNEL, cfqd->queue->node);
+       if (cfqd->root_group)
+               cfq_init_cfqg_base(cfqd->root_group);
+#endif
+       if (!cfqd->root_group) {
                kfree(cfqd);
                return -ENOMEM;
        }
 
-       rcu_read_lock();
+       cfqd->root_group->weight = 2*BLKIO_WEIGHT_DEFAULT;
 
-       cfq_blkiocg_add_blkio_group(&blkio_root_cgroup, &cfqg->blkg,
-                                   cfqd->queue, 0);
-       rcu_read_unlock();
-       cfqd->nr_blkcg_linked_grps++;
-
-       /* Add group on cfqd->cfqg_list */
-       hlist_add_head(&cfqg->cfqd_node, &cfqd->cfqg_list);
-#endif
        /*
         * Not strictly needed (since RB_ROOT just clears the node and we
         * zeroed cfqd on alloc), but better be safe in case someone decides
@@ -3738,14 +3739,14 @@ static int cfq_init_queue(struct request_queue *q)
        /*
         * Our fallback cfqq if cfq_find_alloc_queue() runs into OOM issues.
         * Grab a permanent reference to it, so that the normal code flow
-        * will not attempt to free it.
+        * will not attempt to free it.  oom_cfqq is linked to root_group
+        * but shouldn't hold a reference as it'll never be unlinked.  Lose
+        * the reference from linking right away.
         */
        cfq_init_cfqq(cfqd, &cfqd->oom_cfqq, 1, 0);
        cfqd->oom_cfqq.ref++;
-       cfq_link_cfqq_cfqg(&cfqd->oom_cfqq, &cfqd->root_group);
-
-       cfqd->queue = q;
-       q->elevator->elevator_data = cfqd;
+       cfq_link_cfqq_cfqg(&cfqd->oom_cfqq, cfqd->root_group);
+       cfq_put_cfqg(cfqd->root_group);
 
        init_timer(&cfqd->idle_slice_timer);
        cfqd->idle_slice_timer.function = cfq_idle_slice_timer;