[PATCH V3 6/7] loop: use xarray to store workers

[Ming Lei <ming.lei@redhat.com>]

css->id is unique in io controller wide, so replace rbtree with xarray
for querying/storing 'blkcg_css' by using css->id as key, then code is
simplified a lot.

Acked-by: Dan Schatzberg <schatzberg.dan@gmail.com>
Signed-off-by: Ming Lei <ming.lei@redhat.com>
---
 drivers/block/loop.c | 36 ++++++++++++++----------------------
 drivers/block/loop.h |  3 ++-
 2 files changed, 16 insertions(+), 23 deletions(-)

diff --git a/drivers/block/loop.c b/drivers/block/loop.c
index c9a28483433b..fd07481058e5 100644
--- a/drivers/block/loop.c
+++ b/drivers/block/loop.c
@@ -971,7 +971,6 @@ static void loop_config_discard(struct loop_device *lo)
 }
 
 struct loop_worker {
-	struct rb_node rb_node;
 	struct work_struct work;
 	struct list_head cmd_list;
 	struct list_head idle_list;
@@ -1019,35 +1018,23 @@ static struct cgroup_subsys_state *loop_rq_get_memcg_css(
 
 static void loop_queue_work(struct loop_device *lo, struct loop_cmd *cmd)
 {
-	struct rb_node **node = &(lo->worker_tree.rb_node), *parent = NULL;
-	struct loop_worker *cur_worker, *worker = NULL;
+	struct loop_worker *worker = NULL;
 	struct work_struct *work;
 	struct list_head *cmd_list;
 	struct cgroup_subsys_state *blkcg_css = loop_rq_blkcg_css(cmd);
+	gfp_t gfp = GFP_NOWAIT | __GFP_NOWARN;
 
 	spin_lock(&lo->lo_work_lock);
 
 	if (queue_on_root_worker(blkcg_css))
 		goto queue_work;
 
-	node = &lo->worker_tree.rb_node;
-
-	while (*node) {
-		parent = *node;
-		cur_worker = container_of(*node, struct loop_worker, rb_node);
-		if (cur_worker->blkcg_css == blkcg_css) {
-			worker = cur_worker;
-			break;
-		} else if ((long)cur_worker->blkcg_css < (long)blkcg_css) {
-			node = &(*node)->rb_left;
-		} else {
-			node = &(*node)->rb_right;
-		}
-	}
+	/* css->id is unique in each cgroup subsystem */
+	worker = xa_load(&lo->workers, blkcg_css->id);
 	if (worker)
 		goto queue_work;
 
-	worker = kzalloc(sizeof(struct loop_worker), GFP_NOWAIT | __GFP_NOWARN);
+	worker = kzalloc(sizeof(*worker), gfp);
 	/*
 	 * In the event we cannot allocate a worker, just queue on the
 	 * rootcg worker and issue the I/O as the rootcg
@@ -1061,8 +1048,12 @@ static void loop_queue_work(struct loop_device *lo, struct loop_cmd *cmd)
 	INIT_LIST_HEAD(&worker->cmd_list);
 	INIT_LIST_HEAD(&worker->idle_list);
 	worker->lo = lo;
-	rb_link_node(&worker->rb_node, parent, node);
-	rb_insert_color(&worker->rb_node, &lo->worker_tree);
+
+	if (xa_err(xa_store(&lo->workers, blkcg_css->id, worker, gfp))) {
+		kfree(worker);
+		worker = NULL;
+	}
+
 queue_work:
 	if (worker) {
 		/*
@@ -1218,7 +1209,7 @@ static void __loop_free_idle_workers(struct loop_device *lo, bool force)
 						LOOP_IDLE_WORKER_TIMEOUT))
 			break;
 		list_del(&worker->idle_list);
-		rb_erase(&worker->rb_node, &lo->worker_tree);
+		xa_erase(&lo->workers, worker->blkcg_css->id);
 		css_put(worker->blkcg_css);
 		kfree(worker);
 	}
@@ -1314,7 +1305,7 @@ static int loop_configure(struct loop_device *lo, fmode_t mode,
 	INIT_WORK(&lo->rootcg_work, loop_rootcg_workfn);
 	INIT_LIST_HEAD(&lo->rootcg_cmd_list);
 	INIT_LIST_HEAD(&lo->idle_worker_list);
-	lo->worker_tree = RB_ROOT;
+	xa_init(&lo->workers);
 	INIT_DELAYED_WORK(&lo->idle_work, loop_free_idle_workers);
 	lo->use_dio = lo->lo_flags & LO_FLAGS_DIRECT_IO;
 	lo->lo_device = bdev;
@@ -1416,6 +1407,7 @@ static int __loop_clr_fd(struct loop_device *lo, bool release)
 	destroy_workqueue(lo->workqueue);
 	__loop_free_idle_workers(lo, true);
 	cancel_delayed_work_sync(&lo->idle_work);
+	xa_destroy(&lo->workers);
 
 	spin_lock_irq(&lo->lo_lock);
 	lo->lo_backing_file = NULL;
diff --git a/drivers/block/loop.h b/drivers/block/loop.h
index 9df889af1bcf..cab34da1e1bb 100644
--- a/drivers/block/loop.h
+++ b/drivers/block/loop.h
@@ -14,6 +14,7 @@
 #include <linux/blk-mq.h>
 #include <linux/spinlock.h>
 #include <linux/mutex.h>
+#include <linux/xarray.h>
 #include <uapi/linux/loop.h>
 
 /* Possible states of device */
@@ -59,7 +60,7 @@ struct loop_device {
 	struct work_struct      rootcg_work;
 	struct list_head        rootcg_cmd_list;
 	struct list_head        idle_worker_list;
-	struct rb_root          worker_tree;
+	struct xarray		workers;
 	struct delayed_work	idle_work;
 	bool			use_dio;
 	bool			sysfs_inited;
-- 
2.31.1