[PATCH] fs: direct-io: increase bio refcount as batch

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

Each bio is always submitted to block device one by one,
so it isn't necessary to increase the bio refcount by one
each time with holding dio->bio_lock.

Signed-off-by: Ming Lei <ming.lei@canonical.com>
---
 fs/direct-io.c |   27 +++++++++++++++++----------
 1 file changed, 17 insertions(+), 10 deletions(-)

diff --git a/fs/direct-io.c b/fs/direct-io.c
index 6fb00e3..57b8e73 100644
--- a/fs/direct-io.c
+++ b/fs/direct-io.c
@@ -79,6 +79,8 @@ struct dio_submit {
 	get_block_t *get_block;		/* block mapping function */
 	dio_submit_t *submit_io;	/* IO submition function */
 
+	long	submitted_bio;
+
 	loff_t logical_offset_in_bio;	/* current first logical block in bio */
 	sector_t final_block_in_bio;	/* current final block in bio + 1 */
 	sector_t next_block_for_io;	/* next block to be put under IO,
@@ -121,7 +123,7 @@ struct dio {
 	int is_async;			/* is IO async ? */
 	bool defer_completion;		/* defer AIO completion to workqueue? */
 	int io_error;			/* IO error in completion path */
-	unsigned long refcount;		/* direct_io_worker() and bios */
+	long refcount;			/* direct_io_worker() and bios */
 	struct bio *bio_list;		/* singly linked via bi_private */
 	struct task_struct *waiter;	/* waiting task (NULL if none) */
 
@@ -383,14 +385,9 @@ dio_bio_alloc(struct dio *dio, struct dio_submit *sdio,
 static inline void dio_bio_submit(struct dio *dio, struct dio_submit *sdio)
 {
 	struct bio *bio = sdio->bio;
-	unsigned long flags;
 
 	bio->bi_private = dio;
 
-	spin_lock_irqsave(&dio->bio_lock, flags);
-	dio->refcount++;
-	spin_unlock_irqrestore(&dio->bio_lock, flags);
-
 	if (dio->is_async && dio->rw == READ)
 		bio_set_pages_dirty(bio);
 
@@ -403,15 +400,26 @@ static inline void dio_bio_submit(struct dio *dio, struct dio_submit *sdio)
 	sdio->bio = NULL;
 	sdio->boundary = 0;
 	sdio->logical_offset_in_bio = 0;
+	sdio->submitted_bio++;
 }
 
 /*
  * Release any resources in case of a failure
  */
-static inline void dio_cleanup(struct dio *dio, struct dio_submit *sdio)
+static inline void dio_cleanup(struct dio *dio, struct dio_submit *sdio,
+		bool commit_refcount)
 {
+	unsigned long flags;
+
 	while (sdio->head < sdio->tail)
 		page_cache_release(dio->pages[sdio->head++]);
+
+	if (!commit_refcount)
+		return;
+
+	spin_lock_irqsave(&dio->bio_lock, flags);
+	dio->refcount += (sdio->submitted_bio + 1);
+	spin_unlock_irqrestore(&dio->bio_lock, flags);
 }
 
 /*
@@ -1215,7 +1223,6 @@ do_blockdev_direct_IO(int rw, struct kiocb *iocb, struct inode *inode,
 	dio->i_size = i_size_read(inode);
 
 	spin_lock_init(&dio->bio_lock);
-	dio->refcount = 1;
 
 	sdio.iter = iter;
 	sdio.final_block_in_request =
@@ -1234,7 +1241,7 @@ do_blockdev_direct_IO(int rw, struct kiocb *iocb, struct inode *inode,
 
 	retval = do_direct_IO(dio, &sdio, &map_bh);
 	if (retval)
-		dio_cleanup(dio, &sdio);
+		dio_cleanup(dio, &sdio, false);
 
 	if (retval == -ENOTBLK) {
 		/*
@@ -1267,7 +1274,7 @@ do_blockdev_direct_IO(int rw, struct kiocb *iocb, struct inode *inode,
 	 * It is possible that, we return short IO due to end of file.
 	 * In that case, we need to release all the pages we got hold on.
 	 */
-	dio_cleanup(dio, &sdio);
+	dio_cleanup(dio, &sdio, true);
 
 	/*
 	 * All block lookups have been performed. For READ requests
-- 
1.7.9.5