[RFC PATCH] fs/direct-io.c: Add REQ_NOIDLE for last bio .

[Jianpeng Ma]

For last bio of dio, there are no bio will come.So set REQ_NOIDLE.

Signed-off-by: Jianpeng Ma <majianp...@gmail.com>
---
 fs/direct-io.c |   15 ++++++++++++---
 1 file changed, 12 insertions(+), 3 deletions(-)

diff --git a/fs/direct-io.c b/fs/direct-io.c
index 1faf4cb..7c6958f 100644
--- a/fs/direct-io.c
+++ b/fs/direct-io.c
@@ -127,6 +127,7 @@ struct dio {
        int page_errors;                /* errno from get_user_pages() */
        int is_async;                   /* is IO async ? */
        int io_error;                   /* IO error in completion path */
+       sector_t end_sector;            /* the last sector for this dio */
        unsigned 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) */
@@ -369,21 +370,28 @@ static inline void dio_bio_submit(struct dio *dio, struct 
dio_submit *sdio)
 {
        struct bio *bio = sdio->bio;
        unsigned long flags;
-
+       int rw = dio->rw;
        bio->bi_private = dio;
 
        spin_lock_irqsave(&dio->bio_lock, flags);
        dio->refcount++;
        spin_unlock_irqrestore(&dio->bio_lock, flags);
 
+       /*
+        * If bio is the last for dio,so no bio can arrive for low-level
+        * unless this dio completed.
+        */
+       if (bio->bi_sector + bio_sectors(bio) >= dio->end_sector)
+               rw |= REQ_NOIDLE;
+
        if (dio->is_async && dio->rw == READ)
                bio_set_pages_dirty(bio);
 
        if (sdio->submit_io)
-               sdio->submit_io(dio->rw, bio, dio->inode,
+               sdio->submit_io(rw, bio, dio->inode,
                               sdio->logical_offset_in_bio);
        else
-               submit_bio(dio->rw, bio);
+               submit_bio(rw, bio);
 
        sdio->bio = NULL;
        sdio->boundary = 0;
@@ -1147,6 +1155,7 @@ do_blockdev_direct_IO(int rw, struct kiocb *iocb, struct 
inode *inode,
 
        dio->inode = inode;
        dio->rw = rw;
+       dio->end_sector = end >> 9;
        sdio.blkbits = blkbits;
        sdio.blkfactor = inode->i_blkbits - blkbits;
        sdio.block_in_file = offset >> blkbits;
-- 
1.7.9.5