[PATCH 1/6] loop: clean up blkcg association

[Ming Lei <ming.lei@xxxxxxxxxx>]

Each loop_worker is responsible for running requests originated from
same blkcg, so:

1) associate with kthread in the entry of loop_process_work(), and
disassociate in the end of this function, then we can avoid to do
both for each request.

2) remove ->blkcg_css and ->memcg_css from 'loop_cmd' since both are
per loop_worker.

Cc: Michal Koutný <mkoutny@xxxxxxxx>
Cc: Dan Schatzberg <schatzberg.dan@xxxxxxxxx>
Signed-off-by: Ming Lei <ming.lei@xxxxxxxxxx>
---
 drivers/block/loop.c | 67 ++++++++++++++++++++------------------------
 drivers/block/loop.h |  2 --
 2 files changed, 30 insertions(+), 39 deletions(-)

diff --git a/drivers/block/loop.c b/drivers/block/loop.c
index 02509bc54242..8378b8455f7c 100644
--- a/drivers/block/loop.c
+++ b/drivers/block/loop.c
@@ -949,10 +949,17 @@ static void loop_queue_work(struct loop_device *lo, struct loop_cmd *cmd)
 	struct loop_worker *cur_worker, *worker = NULL;
 	struct work_struct *work;
 	struct list_head *cmd_list;
+	struct cgroup_subsys_state *blkcg_css = NULL;
+#ifdef CONFIG_BLK_CGROUP
+	struct request *rq = blk_mq_rq_from_pdu(cmd);
+
+	if (rq->bio && rq->bio->bi_blkg)
+		blkcg_css = &bio_blkcg(rq->bio)->css;
+#endif
 
 	spin_lock_irq(&lo->lo_work_lock);
 
-	if (queue_on_root_worker(cmd->blkcg_css))
+	if (queue_on_root_worker(blkcg_css))
 		goto queue_work;
 
 	node = &lo->worker_tree.rb_node;
@@ -960,10 +967,10 @@ static void loop_queue_work(struct loop_device *lo, struct loop_cmd *cmd)
 	while (*node) {
 		parent = *node;
 		cur_worker = container_of(*node, struct loop_worker, rb_node);
-		if (cur_worker->blkcg_css == cmd->blkcg_css) {
+		if (cur_worker->blkcg_css == blkcg_css) {
 			worker = cur_worker;
 			break;
-		} else if ((long)cur_worker->blkcg_css < (long)cmd->blkcg_css) {
+		} else if ((long)cur_worker->blkcg_css < (long)blkcg_css) {
 			node = &(*node)->rb_left;
 		} else {
 			node = &(*node)->rb_right;
@@ -977,15 +984,10 @@ static void loop_queue_work(struct loop_device *lo, struct loop_cmd *cmd)
 	 * In the event we cannot allocate a worker, just queue on the
 	 * rootcg worker and issue the I/O as the rootcg
 	 */
-	if (!worker) {
-		cmd->blkcg_css = NULL;
-		if (cmd->memcg_css)
-			css_put(cmd->memcg_css);
-		cmd->memcg_css = NULL;
+	if (!worker)
 		goto queue_work;
-	}
 
-	worker->blkcg_css = cmd->blkcg_css;
+	worker->blkcg_css = blkcg_css;
 	css_get(worker->blkcg_css);
 	INIT_WORK(&worker->work, loop_workfn);
 	INIT_LIST_HEAD(&worker->cmd_list);
@@ -2100,19 +2102,6 @@ static blk_status_t loop_queue_rq(struct blk_mq_hw_ctx *hctx,
 		break;
 	}
 
-	/* always use the first bio's css */
-	cmd->blkcg_css = NULL;
-	cmd->memcg_css = NULL;
-#ifdef CONFIG_BLK_CGROUP
-	if (rq->bio && rq->bio->bi_blkg) {
-		cmd->blkcg_css = &bio_blkcg(rq->bio)->css;
-#ifdef CONFIG_MEMCG
-		cmd->memcg_css =
-			cgroup_get_e_css(cmd->blkcg_css->cgroup,
-					&memory_cgrp_subsys);
-#endif
-	}
-#endif
 	loop_queue_work(lo, cmd);
 
 	return BLK_STS_OK;
@@ -2124,28 +2113,14 @@ static void loop_handle_cmd(struct loop_cmd *cmd)
 	const bool write = op_is_write(req_op(rq));
 	struct loop_device *lo = rq->q->queuedata;
 	int ret = 0;
-	struct mem_cgroup *old_memcg = NULL;
 
 	if (write && (lo->lo_flags & LO_FLAGS_READ_ONLY)) {
 		ret = -EIO;
 		goto failed;
 	}
 
-	if (cmd->blkcg_css)
-		kthread_associate_blkcg(cmd->blkcg_css);
-	if (cmd->memcg_css)
-		old_memcg = set_active_memcg(
-			mem_cgroup_from_css(cmd->memcg_css));
-
 	ret = do_req_filebacked(lo, rq);
 
-	if (cmd->blkcg_css)
-		kthread_associate_blkcg(NULL);
-
-	if (cmd->memcg_css) {
-		set_active_memcg(old_memcg);
-		css_put(cmd->memcg_css);
-	}
  failed:
 	/* complete non-aio request */
 	if (!cmd->use_aio || ret) {
@@ -2201,7 +2176,25 @@ static void loop_workfn(struct work_struct *work)
 {
 	struct loop_worker *worker =
 		container_of(work, struct loop_worker, work);
+	struct mem_cgroup *old_memcg = NULL;
+	struct cgroup_subsys_state *memcg_css = NULL;
+
+	kthread_associate_blkcg(worker->blkcg_css);
+#ifdef CONFIG_MEMCG
+	memcg_css = cgroup_get_e_css(worker->blkcg_css->cgroup,
+			&memory_cgrp_subsys);
+#endif
+	if (memcg_css)
+		old_memcg = set_active_memcg(
+				mem_cgroup_from_css(memcg_css));
+
 	loop_process_work(worker, &worker->cmd_list, worker->lo);
+
+	kthread_associate_blkcg(NULL);
+	if (memcg_css) {
+		set_active_memcg(old_memcg);
+		css_put(memcg_css);
+	}
 }
 
 static void loop_rootcg_workfn(struct work_struct *work)
diff --git a/drivers/block/loop.h b/drivers/block/loop.h
index 1988899db63a..a52a3fd89457 100644
--- a/drivers/block/loop.h
+++ b/drivers/block/loop.h
@@ -77,8 +77,6 @@ struct loop_cmd {
 	long ret;
 	struct kiocb iocb;
 	struct bio_vec *bvec;
-	struct cgroup_subsys_state *blkcg_css;
-	struct cgroup_subsys_state *memcg_css;
 };
 
 /* Support for loadable transfer modules */
-- 
2.31.1