raid5-cache: use bio chaining

Simplify the bio completion handler by using bio chaining and submitting
bios as soon as they are full.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Shaohua Li <shli@fb.com>
Signed-off-by: NeilBrown <neilb@suse.com>

drivers/md/raid5-cache.c

@@ -100,8 +100,6 @@ struct r5l_io_unit {
 	struct page *meta_page;	/* store meta block */
 	int meta_offset;	/* current offset in meta_page */
 
-	struct bio_list bios;
-	atomic_t pending_io;	/* pending bios not written to log yet */
 	struct bio *current_bio;/* current_bio accepting new data */
 
 	atomic_t pending_stripe;/* how many stripes not flushed to raid */
@@ -112,6 +110,7 @@ struct r5l_io_unit {
 	struct list_head stripe_list; /* stripes added to the io_unit */
 
 	int state;
+	bool need_split_bio;
 };
 
 /* r5l_io_unit state */
@@ -215,9 +214,6 @@ static void r5l_log_endio(struct bio *bio)
 
 	bio_put(bio);
 
-	if (!atomic_dec_and_test(&io->pending_io))
-		return;
-
 	spin_lock_irqsave(&log->io_list_lock, flags);
 	__r5l_set_io_unit_state(io, IO_UNIT_IO_END);
 	if (log->need_cache_flush)
@@ -235,7 +231,6 @@ static void r5l_submit_current_io(struct r5l_log *log)
 {
 	struct r5l_io_unit *io = log->current_io;
 	struct r5l_meta_block *block;
-	struct bio *bio;
 	unsigned long flags;
 	u32 crc;
 
@@ -252,22 +247,17 @@ static void r5l_submit_current_io(struct r5l_log *log)
 	__r5l_set_io_unit_state(io, IO_UNIT_IO_START);
 	spin_unlock_irqrestore(&log->io_list_lock, flags);
 
-	while ((bio = bio_list_pop(&io->bios)))
-		submit_bio(WRITE, bio);
+	submit_bio(WRITE, io->current_bio);
 }
 
-static struct bio *r5l_bio_alloc(struct r5l_log *log, struct r5l_io_unit *io)
+static struct bio *r5l_bio_alloc(struct r5l_log *log)
 {
 	struct bio *bio = bio_kmalloc(GFP_NOIO | __GFP_NOFAIL, BIO_MAX_PAGES);
 
 	bio->bi_rw = WRITE;
 	bio->bi_bdev = log->rdev->bdev;
 	bio->bi_iter.bi_sector = log->rdev->data_offset + log->log_start;
-	bio->bi_end_io = r5l_log_endio;
-	bio->bi_private = io;
 
-	bio_list_add(&io->bios, bio);
-	atomic_inc(&io->pending_io);
 	return bio;
 }
 
@@ -283,7 +273,7 @@ static void r5_reserve_log_entry(struct r5l_log *log, struct r5l_io_unit *io)
 	 * of BLOCK_SECTORS.
 	 */
 	if (log->log_start == 0)
-		io->current_bio = NULL;
+		io->need_split_bio = true;
 
 	io->log_end = log->log_start;
 }
@@ -296,7 +286,6 @@ static struct r5l_io_unit *r5l_new_meta(struct r5l_log *log)
 	/* We can't handle memory allocate failure so far */
 	io = kmem_cache_zalloc(log->io_kc, GFP_NOIO | __GFP_NOFAIL);
 	io->log = log;
-	bio_list_init(&io->bios);
 	INIT_LIST_HEAD(&io->log_sibling);
 	INIT_LIST_HEAD(&io->stripe_list);
 	io->state = IO_UNIT_RUNNING;
@@ -312,7 +301,9 @@ static struct r5l_io_unit *r5l_new_meta(struct r5l_log *log)
 	io->meta_offset = sizeof(struct r5l_meta_block);
 	io->seq = log->seq++;
 
-	io->current_bio = r5l_bio_alloc(log, io);
+	io->current_bio = r5l_bio_alloc(log);
+	io->current_bio->bi_end_io = r5l_log_endio;
+	io->current_bio->bi_private = io;
 	bio_add_page(io->current_bio, io->meta_page, PAGE_SIZE, 0);
 
 	r5_reserve_log_entry(log, io);
@@ -361,15 +352,18 @@ static void r5l_append_payload_page(struct r5l_log *log, struct page *page)
 {
 	struct r5l_io_unit *io = log->current_io;
 
-alloc_bio:
-	if (!io->current_bio)
-		io->current_bio = r5l_bio_alloc(log, io);
+	if (io->need_split_bio) {
+		struct bio *prev = io->current_bio;
 
-	if (!bio_add_page(io->current_bio, page, PAGE_SIZE, 0)) {
-		io->current_bio = NULL;
-		goto alloc_bio;
+		io->current_bio = r5l_bio_alloc(log);
+		bio_chain(io->current_bio, prev);
+
+		submit_bio(WRITE, prev);
 	}
 
+	if (!bio_add_page(io->current_bio, page, PAGE_SIZE, 0))
+		BUG();
+
 	r5_reserve_log_entry(log, io);
 }