[PATCH V4 2/7] loop: clean up blkcg association

Ming Lei
2021-08-06T08:03:55Z

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.

Also kill #ifdef in the related functions.

Acked-by: Dan Schatzberg <schatzberg.dan@gmail.com>
Signed-off-by: Ming Lei <ming.lei@redhat.com>
---
drivers/block/loop.c | 81 +++++++++++++++++++++++---------------------
drivers/block/loop.h | 2 --
2 files changed, 43 insertions(+), 40 deletions(-)

diff --git a/drivers/block/loop.c b/drivers/block/loop.c
index fa1c298a8cfb..0df2a6add598 100644
--- a/drivers/block/loop.c
+++ b/drivers/block/loop.c
@@ -989,23 +989,46 @@ static inline int queue_on_root_worker(struct cgroup_subsys_state *css)
{
return !css || css == blkcg_root_css;
}
+static struct cgroup_subsys_state *loop_rq_blkcg_css(struct loop_cmd *cmd)
+{
+ struct request *rq = blk_mq_rq_from_pdu(cmd);
+ /* always use the first bio's css */
+ struct blkcg *blkcg = bio_blkcg(rq->bio);
+
+ if (blkcg)
+ return &blkcg->css;
+ return NULL;
+}
#else
static inline int queue_on_root_worker(struct cgroup_subsys_state *css)
{
return !css;
}
+static struct cgroup_subsys_state *loop_rq_blkcg_css(struct loop_cmd *cmd)
+{
+ return NULL;
+}
#endif

+static struct cgroup_subsys_state *loop_rq_get_memcg_css(
+ struct cgroup_subsys_state *blkcg_css)
+{
+ if (blkcg_css)
+ return memcg_get_e_css(blkcg_css);
+ return NULL;
+}
+
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 work_struct *work;
struct list_head *cmd_list;
+ struct cgroup_subsys_state *blkcg_css = loop_rq_blkcg_css(cmd);

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;
@@ -1013,10 +1036,10 @@ 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;
@@ -1030,15 +1053,10 @@ 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);
@@ -2162,19 +2180,6 @@ 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;
@@ -2186,28 +2191,14 @@ 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) {
@@ -2263,7 +2254,21 @@ static void loop_workfn(struct work_struct *work)
{
struct loop_worker *worker =
container_of(work, struct loop_worker, work);
- loop_process_work(worker, &worker->cmd_list, worker->lo);
+ struct mem_cgroup *old_memcg = NULL;
+ struct cgroup_subsys_state *memcg_css = NULL;
+
+ kthread_associate_blkcg(worker->blkcg_css);
+ memcg_css = loop_rq_get_memcg_css(worker->blkcg_css);
+ if (memcg_css) {
+ old_memcg = set_active_memcg(
+ mem_cgroup_from_css(memcg_css));
+ loop_process_work(worker, &worker->cmd_list, worker->lo);
+ set_active_memcg(old_memcg);
+ css_put(memcg_css);
+ } else {
+ loop_process_work(worker, &worker->cmd_list, worker->lo);
+ }
+ kthread_associate_blkcg(NULL);
}

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