block, cfq: move icq creation and rq->elv.icq association to block core

Now block layer knows everything necessary to create and associate
icq's with requests.  Move ioc_create_icq() to blk-ioc.c and update
get_request() such that, if elevator_type->icq_size is set, requests
are automatically associated with their matching icq's before
elv_set_request().  io_context reference is also managed by block core
on request alloc/free.

* Only ioprio/cgroup changed handling remains from cfq_get_cic().
  Collapsed into cfq_set_request().

* This removes queue kicking on icq allocation failure (for now).  As
  icq allocation failure is rare and the only effect of queue kicking
  achieved was possibily accelerating queue processing, this change
  shouldn't be noticeable.

  There is a larger underlying problem.  Unlike request allocation,
  icq allocation is not guaranteed to succeed eventually after
  retries.  The number of icq is unbound and thus mempool can't be the
  solution either.  This effectively adds allocation dependency on
  memory free path and thus possibility of deadlock.

  This usually wouldn't happen because icq allocation is not a hot
  path and, even when the condition triggers, it's highly unlikely
  that none of the writeback workers already has icq.

  However, this is still possible especially if elevator is being
  switched under high memory pressure, so we better get it fixed.
  Probably the only solution is just bypassing elevator and appending
  to dispatch queue on any elevator allocation failure.

* Comment added to explain how icq's are managed and synchronized.

This completes cleanup of io_context interface.

Signed-off-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

1 files changed, 59 insertions, 1 deletions

diff --git a/block/blk-ioc.c b/block/blk-ioc.c
index 0910a5584d38..c04d16b02225 100644
--- a/block/blk-ioc.c
+++ b/block/blk-ioc.c
@@ -289,7 +289,6 @@ void create_io_context_slowpath(struct task_struct *task, gfp_t gfp_flags,
 		kmem_cache_free(iocontext_cachep, ioc);
 	task_unlock(task);
 }
-EXPORT_SYMBOL(create_io_context_slowpath);
 
 /**
  * get_task_io_context - get io_context of a task
@@ -362,6 +361,65 @@ out:
 }
 EXPORT_SYMBOL(ioc_lookup_icq);
 
+/**
+ * ioc_create_icq - create and link io_cq
+ * @q: request_queue of interest
+ * @gfp_mask: allocation mask
+ *
+ * Make sure io_cq linking %current->io_context and @q exists.  If either
+ * io_context and/or icq don't exist, they will be created using @gfp_mask.
+ *
+ * The caller is responsible for ensuring @ioc won't go away and @q is
+ * alive and will stay alive until this function returns.
+ */
+struct io_cq *ioc_create_icq(struct request_queue *q, gfp_t gfp_mask)
+{
+	struct elevator_type *et = q->elevator->type;
+	struct io_context *ioc;
+	struct io_cq *icq;
+
+	/* allocate stuff */
+	ioc = create_io_context(current, gfp_mask, q->node);
+	if (!ioc)
+		return NULL;
+
+	icq = kmem_cache_alloc_node(et->icq_cache, gfp_mask | __GFP_ZERO,
+				    q->node);
+	if (!icq)
+		return NULL;
+
+	if (radix_tree_preload(gfp_mask) < 0) {
+		kmem_cache_free(et->icq_cache, icq);
+		return NULL;
+	}
+
+	icq->ioc = ioc;
+	icq->q = q;
+	INIT_LIST_HEAD(&icq->q_node);
+	INIT_HLIST_NODE(&icq->ioc_node);
+
+	/* lock both q and ioc and try to link @icq */
+	spin_lock_irq(q->queue_lock);
+	spin_lock(&ioc->lock);
+
+	if (likely(!radix_tree_insert(&ioc->icq_tree, q->id, icq))) {
+		hlist_add_head(&icq->ioc_node, &ioc->icq_list);
+		list_add(&icq->q_node, &q->icq_list);
+		if (et->ops.elevator_init_icq_fn)
+			et->ops.elevator_init_icq_fn(icq);
+	} else {
+		kmem_cache_free(et->icq_cache, icq);
+		icq = ioc_lookup_icq(ioc, q);
+		if (!icq)
+			printk(KERN_ERR "cfq: icq link failed!\n");
+	}
+
+	spin_unlock(&ioc->lock);
+	spin_unlock_irq(q->queue_lock);
+	radix_tree_preload_end();
+	return icq;
+}
+
 void ioc_set_changed(struct io_context *ioc, int which)
 {
 	struct io_cq *icq;