---

yaml
---
r: 320918
b: refs/heads/master
c: a051661
h: refs/heads/master
v: v3

[refs]

@@ -1,2 +1,2 @@
 ---
-refs/heads/master: 5b788ce3e2acac9bf109743b1281d77347cf2101
+refs/heads/master: a051661ca6d134c18599498b185b667859d4339b

trunk/Documentation/block/queue-sysfs.txt

@@ -38,6 +38,13 @@ read or write requests. Note that the total allocated number may be twice
 this amount, since it applies only to reads or writes (not the accumulated
 sum).
 
+To avoid priority inversion through request starvation, a request
+queue maintains a separate request pool per each cgroup when
+CONFIG_BLK_CGROUP is enabled, and this parameter applies to each such
+per-block-cgroup request pool.  IOW, if there are N block cgroups,
+each request queue may have upto N request pools, each independently
+regulated by nr_requests.
+
 read_ahead_kb (RW)
 ------------------
 Maximum number of kilobytes to read-ahead for filesystems on this block

trunk/block/blk-cgroup.c

@@ -63,6 +63,7 @@ static void blkg_free(struct blkcg_gq *blkg)
 		kfree(pd);
 	}
 
+	blk_exit_rl(&blkg->rl);
 	kfree(blkg);
 }
 
@@ -90,6 +91,13 @@ static struct blkcg_gq *blkg_alloc(struct blkcg *blkcg, struct request_queue *q,
 	blkg->blkcg = blkcg;
 	blkg->refcnt = 1;
 
+	/* root blkg uses @q->root_rl, init rl only for !root blkgs */
+	if (blkcg != &blkcg_root) {
+		if (blk_init_rl(&blkg->rl, q, gfp_mask))
+			goto err_free;
+		blkg->rl.blkg = blkg;
+	}
+
 	for (i = 0; i < BLKCG_MAX_POLS; i++) {
 		struct blkcg_policy *pol = blkcg_policy[i];
 		struct blkg_policy_data *pd;
@@ -99,10 +107,8 @@ static struct blkcg_gq *blkg_alloc(struct blkcg *blkcg, struct request_queue *q,
 
 		/* alloc per-policy data and attach it to blkg */
 		pd = kzalloc_node(pol->pd_size, gfp_mask, q->node);
-		if (!pd) {
-			blkg_free(blkg);
-			return NULL;
-		}
+		if (!pd)
+			goto err_free;
 
 		blkg->pd[i] = pd;
 		pd->blkg = blkg;
@@ -113,6 +119,10 @@ static struct blkcg_gq *blkg_alloc(struct blkcg *blkcg, struct request_queue *q,
 	}
 
 	return blkg;
+
+err_free:
+	blkg_free(blkg);
+	return NULL;
 }
 
 static struct blkcg_gq *__blkg_lookup(struct blkcg *blkcg,
@@ -300,6 +310,38 @@ void __blkg_release(struct blkcg_gq *blkg)
 }
 EXPORT_SYMBOL_GPL(__blkg_release);
 
+/*
+ * The next function used by blk_queue_for_each_rl().  It's a bit tricky
+ * because the root blkg uses @q->root_rl instead of its own rl.
+ */
+struct request_list *__blk_queue_next_rl(struct request_list *rl,
+					 struct request_queue *q)
+{
+	struct list_head *ent;
+	struct blkcg_gq *blkg;
+
+	/*
+	 * Determine the current blkg list_head.  The first entry is
+	 * root_rl which is off @q->blkg_list and mapped to the head.
+	 */
+	if (rl == &q->root_rl) {
+		ent = &q->blkg_list;
+	} else {
+		blkg = container_of(rl, struct blkcg_gq, rl);
+		ent = &blkg->q_node;
+	}
+
+	/* walk to the next list_head, skip root blkcg */
+	ent = ent->next;
+	if (ent == &q->root_blkg->q_node)
+		ent = ent->next;
+	if (ent == &q->blkg_list)
+		return NULL;
+
+	blkg = container_of(ent, struct blkcg_gq, q_node);
+	return &blkg->rl;
+}
+
 static int blkcg_reset_stats(struct cgroup *cgroup, struct cftype *cftype,
 			     u64 val)
 {
@@ -750,6 +792,7 @@ int blkcg_activate_policy(struct request_queue *q,
 		goto out_unlock;
 	}
 	q->root_blkg = blkg;
+	q->root_rl.blkg = blkg;
 
 	list_for_each_entry(blkg, &q->blkg_list, q_node)
 		cnt++;

trunk/block/blk-cgroup.h

@@ -17,6 +17,7 @@
 #include <linux/u64_stats_sync.h>
 #include <linux/seq_file.h>
 #include <linux/radix-tree.h>
+#include <linux/blkdev.h>
 
 /* Max limits for throttle policy */
 #define THROTL_IOPS_MAX		UINT_MAX
@@ -93,6 +94,8 @@ struct blkcg_gq {
 	struct list_head		q_node;
 	struct hlist_node		blkcg_node;
 	struct blkcg			*blkcg;
+	/* request allocation list for this blkcg-q pair */
+	struct request_list		rl;
 	/* reference count */
 	int				refcnt;
 
@@ -250,6 +253,95 @@ static inline void blkg_put(struct blkcg_gq *blkg)
 		__blkg_release(blkg);
 }
 
+/**
+ * blk_get_rl - get request_list to use
+ * @q: request_queue of interest
+ * @bio: bio which will be attached to the allocated request (may be %NULL)
+ *
+ * The caller wants to allocate a request from @q to use for @bio.  Find
+ * the request_list to use and obtain a reference on it.  Should be called
+ * under queue_lock.  This function is guaranteed to return non-%NULL
+ * request_list.
+ */
+static inline struct request_list *blk_get_rl(struct request_queue *q,
+					      struct bio *bio)
+{
+	struct blkcg *blkcg;
+	struct blkcg_gq *blkg;
+
+	rcu_read_lock();
+
+	blkcg = bio_blkcg(bio);
+
+	/* bypass blkg lookup and use @q->root_rl directly for root */
+	if (blkcg == &blkcg_root)
+		goto root_rl;
+
+	/*
+	 * Try to use blkg->rl.  blkg lookup may fail under memory pressure
+	 * or if either the blkcg or queue is going away.  Fall back to
+	 * root_rl in such cases.
+	 */
+	blkg = blkg_lookup_create(blkcg, q);
+	if (unlikely(IS_ERR(blkg)))
+		goto root_rl;
+
+	blkg_get(blkg);
+	rcu_read_unlock();
+	return &blkg->rl;
+root_rl:
+	rcu_read_unlock();
+	return &q->root_rl;
+}
+
+/**
+ * blk_put_rl - put request_list
+ * @rl: request_list to put
+ *
+ * Put the reference acquired by blk_get_rl().  Should be called under
+ * queue_lock.
+ */
+static inline void blk_put_rl(struct request_list *rl)
+{
+	/* root_rl may not have blkg set */
+	if (rl->blkg && rl->blkg->blkcg != &blkcg_root)
+		blkg_put(rl->blkg);
+}
+
+/**
+ * blk_rq_set_rl - associate a request with a request_list
+ * @rq: request of interest
+ * @rl: target request_list
+ *
+ * Associate @rq with @rl so that accounting and freeing can know the
+ * request_list @rq came from.
+ */
+static inline void blk_rq_set_rl(struct request *rq, struct request_list *rl)
+{
+	rq->rl = rl;
+}
+
+/**
+ * blk_rq_rl - return the request_list a request came from
+ * @rq: request of interest
+ *
+ * Return the request_list @rq is allocated from.
+ */
+static inline struct request_list *blk_rq_rl(struct request *rq)
+{
+	return rq->rl;
+}
+
+struct request_list *__blk_queue_next_rl(struct request_list *rl,
+					 struct request_queue *q);
+/**
+ * blk_queue_for_each_rl - iterate through all request_lists of a request_queue
+ *
+ * Should be used under queue_lock.
+ */
+#define blk_queue_for_each_rl(rl, q)	\
+	for ((rl) = &(q)->root_rl; (rl); (rl) = __blk_queue_next_rl((rl), (q)))
+
 /**
  * blkg_stat_add - add a value to a blkg_stat
  * @stat: target blkg_stat
@@ -392,12 +484,22 @@ static inline void blkcg_deactivate_policy(struct request_queue *q,
 
 static inline struct blkcg *cgroup_to_blkcg(struct cgroup *cgroup) { return NULL; }
 static inline struct blkcg *bio_blkcg(struct bio *bio) { return NULL; }
+
 static inline struct blkg_policy_data *blkg_to_pd(struct blkcg_gq *blkg,
 						  struct blkcg_policy *pol) { return NULL; }
 static inline struct blkcg_gq *pd_to_blkg(struct blkg_policy_data *pd) { return NULL; }
 static inline char *blkg_path(struct blkcg_gq *blkg) { return NULL; }
 static inline void blkg_get(struct blkcg_gq *blkg) { }
 static inline void blkg_put(struct blkcg_gq *blkg) { }
 
+static inline struct request_list *blk_get_rl(struct request_queue *q,
+					      struct bio *bio) { return &q->root_rl; }
+static inline void blk_put_rl(struct request_list *rl) { }
+static inline void blk_rq_set_rl(struct request *rq, struct request_list *rl) { }
+static inline struct request_list *blk_rq_rl(struct request *rq) { return &rq->q->root_rl; }
+
+#define blk_queue_for_each_rl(rl, q)	\
+	for ((rl) = &(q)->root_rl; (rl); (rl) = NULL)
+
 #endif	/* CONFIG_BLK_CGROUP */
 #endif	/* _BLK_CGROUP_H */

trunk/block/blk-core.c

@@ -416,9 +416,14 @@ void blk_drain_queue(struct request_queue *q, bool drain_all)
 	 * left with hung waiters. We need to wake up those waiters.
 	 */
 	if (q->request_fn) {
+		struct request_list *rl;
+
 		spin_lock_irq(q->queue_lock);
-		for (i = 0; i < ARRAY_SIZE(q->rq.wait); i++)
-			wake_up_all(&q->rq.wait[i]);
+
+		blk_queue_for_each_rl(rl, q)
+			for (i = 0; i < ARRAY_SIZE(rl->wait); i++)
+				wake_up_all(&rl->wait[i]);
+
 		spin_unlock_irq(q->queue_lock);
 	}
 }
@@ -685,7 +690,7 @@ blk_init_allocated_queue(struct request_queue *q, request_fn_proc *rfn,
 	if (!q)
 		return NULL;
 
-	if (blk_init_rl(&q->rq, q, GFP_KERNEL))
+	if (blk_init_rl(&q->root_rl, q, GFP_KERNEL))
 		return NULL;
 
 	q->request_fn		= rfn;
@@ -776,7 +781,12 @@ static void __freed_request(struct request_list *rl, int sync)
 {
 	struct request_queue *q = rl->q;
 
-	if (rl->count[sync] < queue_congestion_off_threshold(q))
+	/*
+	 * bdi isn't aware of blkcg yet.  As all async IOs end up root
+	 * blkcg anyway, just use root blkcg state.
+	 */
+	if (rl == &q->root_rl &&
+	    rl->count[sync] < queue_congestion_off_threshold(q))
 		blk_clear_queue_congested(q, sync);
 
 	if (rl->count[sync] + 1 <= q->nr_requests) {
@@ -897,7 +907,12 @@ static struct request *__get_request(struct request_list *rl, int rw_flags,
 				}
 			}
 		}
-		blk_set_queue_congested(q, is_sync);
+		/*
+		 * bdi isn't aware of blkcg yet.  As all async IOs end up
+		 * root blkcg anyway, just use root blkcg state.
+		 */
+		if (rl == &q->root_rl)
+			blk_set_queue_congested(q, is_sync);
 	}
 
 	/*
@@ -939,6 +954,7 @@ static struct request *__get_request(struct request_list *rl, int rw_flags,
 		goto fail_alloc;
 
 	blk_rq_init(q, rq);
+	blk_rq_set_rl(rq, rl);
 	rq->cmd_flags = rw_flags | REQ_ALLOCED;
 
 	/* init elvpriv */
@@ -1032,15 +1048,19 @@ static struct request *get_request(struct request_queue *q, int rw_flags,
 {
 	const bool is_sync = rw_is_sync(rw_flags) != 0;
 	DEFINE_WAIT(wait);
-	struct request_list *rl = &q->rq;
+	struct request_list *rl;
 	struct request *rq;
+
+	rl = blk_get_rl(q, bio);	/* transferred to @rq on success */
 retry:
-	rq = __get_request(&q->rq, rw_flags, bio, gfp_mask);
+	rq = __get_request(rl, rw_flags, bio, gfp_mask);
 	if (rq)
 		return rq;
 
-	if (!(gfp_mask & __GFP_WAIT) || unlikely(blk_queue_dead(q)))
+	if (!(gfp_mask & __GFP_WAIT) || unlikely(blk_queue_dead(q))) {
+		blk_put_rl(rl);
 		return NULL;
+	}
 
 	/* wait on @rl and retry */
 	prepare_to_wait_exclusive(&rl->wait[is_sync], &wait,
@@ -1231,12 +1251,14 @@ void __blk_put_request(struct request_queue *q, struct request *req)
 	 */
 	if (req->cmd_flags & REQ_ALLOCED) {
 		unsigned int flags = req->cmd_flags;
+		struct request_list *rl = blk_rq_rl(req);
 
 		BUG_ON(!list_empty(&req->queuelist));
 		BUG_ON(!hlist_unhashed(&req->hash));
 
-		blk_free_request(&q->rq, req);
-		freed_request(&q->rq, flags);
+		blk_free_request(rl, req);
+		freed_request(rl, flags);
+		blk_put_rl(rl);
 	}
 }
 EXPORT_SYMBOL_GPL(__blk_put_request);