[PATCH 8/8] dm: put all polled io into one single list

Ming Lei
2022-04-12T10:10:08Z

If bio_split() isn't involved, it is a bit overkill to link dm_io into hlist,
given there is only single dm_io in the list, so convert to single list
for holding all dm_io instances associated with this bio.

Signed-off-by: Ming Lei <ming.lei@redhat.com>
---
drivers/md/dm-core.h | 2 +-
drivers/md/dm.c | 46 +++++++++++++++++++++++---------------------
2 files changed, 25 insertions(+), 23 deletions(-)

diff --git a/drivers/md/dm-core.h b/drivers/md/dm-core.h
index 811c0ccbc63d..7f51957913e8 100644
--- a/drivers/md/dm-core.h
+++ b/drivers/md/dm-core.h
@@ -257,7 +257,7 @@ struct dm_io {
spinlock_t lock;
unsigned long start_time;
void *data;
- struct hlist_node node;
+ struct dm_io *next;
struct task_struct *map_task;
struct dm_stats_aux stats_aux;
/* last member of dm_target_io is 'struct bio' */
diff --git a/drivers/md/dm.c b/drivers/md/dm.c
index 2987f7cf7b47..db23efd6bbf6 100644
--- a/drivers/md/dm.c
+++ b/drivers/md/dm.c
@@ -1492,7 +1492,7 @@ static bool __process_abnormal_io(struct clone_info *ci, struct dm_target *ti,
}

/*
- * Reuse ->bi_private as hlist head for storing all dm_io instances
+ * Reuse ->bi_private as dm_io list head for storing all dm_io instances
* associated with this bio, and this bio's bi_private needs to be
* stored in dm_io->data before the reuse.
*
@@ -1500,14 +1500,14 @@ static bool __process_abnormal_io(struct clone_info *ci, struct dm_target *ti,
* touch it after splitting. Meantime it won't be changed by anyone after
* bio is submitted. So this reuse is safe.
*/
-static inline struct hlist_head *dm_get_bio_hlist_head(struct bio *bio)
+static inline struct dm_io **dm_poll_list_head(struct bio *bio)
{
- return (struct hlist_head *)&bio->bi_private;
+ return (struct dm_io **)&bio->bi_private;
}

static void dm_queue_poll_io(struct bio *bio, struct dm_io *io)
{
- struct hlist_head *head = dm_get_bio_hlist_head(bio);
+ struct dm_io **head = dm_poll_list_head(bio);

if (!(bio->bi_opf & REQ_DM_POLL_LIST)) {
bio->bi_opf |= REQ_DM_POLL_LIST;
@@ -1517,19 +1517,20 @@ static void dm_queue_poll_io(struct bio *bio, struct dm_io *io)
*/
io->data = bio->bi_private;

- INIT_HLIST_HEAD(head);
-
/* tell block layer to poll for completion */
bio->bi_cookie = ~BLK_QC_T_NONE;
+
+ io->next = NULL;
} else {
/*
* bio recursed due to split, reuse original poll list,
* and save bio->bi_private too.
*/
- io->data = hlist_entry(head->first, struct dm_io, node)->data;
+ io->data = (*head)->data;
+ io->next = *head;
}

- hlist_add_head(&io->node, head);
+ *head = io;
}

/*
@@ -1682,18 +1683,16 @@ static bool dm_poll_dm_io(struct dm_io *io, struct io_comp_batch *iob,
static int dm_poll_bio(struct bio *bio, struct io_comp_batch *iob,
unsigned int flags)
{
- struct hlist_head *head = dm_get_bio_hlist_head(bio);
- struct hlist_head tmp = HLIST_HEAD_INIT;
- struct hlist_node *next;
- struct dm_io *io;
+ struct dm_io **head = dm_poll_list_head(bio);
+ struct dm_io *list = *head;
+ struct dm_io *tmp = NULL;
+ struct dm_io *curr, *next;

/* Only poll normal bio which was marked as REQ_DM_POLL_LIST */
if (!(bio->bi_opf & REQ_DM_POLL_LIST))
return 0;

- WARN_ON_ONCE(hlist_empty(head));
-
- hlist_move_list(head, &tmp);
+ WARN_ON_ONCE(!list);

/*
* Restore .bi_private before possibly completing dm_io.
@@ -1704,24 +1703,27 @@ static int dm_poll_bio(struct bio *bio, struct io_comp_batch *iob,
* clearing REQ_DM_POLL_LIST here.
*/
bio->bi_opf &= ~REQ_DM_POLL_LIST;
- bio->bi_private = hlist_entry(tmp.first, struct dm_io, node)->data;
+ bio->bi_private = list->data;

- hlist_for_each_entry_safe(io, next, &tmp, node) {
- if (dm_poll_dm_io(io, iob, flags)) {
- hlist_del_init(&io->node);
+ for (curr = list, next = curr->next; curr; curr = next, next =
+ curr ? curr->next : NULL) {
+ if (dm_poll_dm_io(curr, iob, flags)) {
/*
* clone_endio() has already occurred, so passing
* error as 0 here doesn't override io->status
*/
- dm_io_dec_pending(io, 0);
+ dm_io_dec_pending(curr, 0);
+ } else {
+ curr->next = tmp;
+ tmp = curr;
}
}

/* Not done? */
- if (!hlist_empty(&tmp)) {
+ if (tmp) {
bio->bi_opf |= REQ_DM_POLL_LIST;
/* Reset bio->bi_private to dm_io list head */
- hlist_move_list(&tmp, head);
+ *head = tmp;
return 0;
}
return 1;
--
2.31.1