block: save 8 bytes of space in struct blkdev_dio

The members 'waiter' and 'iocb' are mutually exclusive, since one
of them is for sync IO and the other for async. So put them in
a union.

Signed-off-by: Jens Axboe <axboe@fb.com>

diff --git a/fs/block_dev.c b/fs/block_dev.c
index 1f7584d141f83ef0dd3aa963f6b7463a7cb0bcf1..c642f04198b00a7cc2f69fec324d8182c0090a1f 100644 (file)
--- a/fs/block_dev.c
+++ b/fs/block_dev.c
@@ -272,12 +272,15 @@ __blkdev_direct_IO_simple(struct kiocb *iocb, struct iov_iter *iter,
 }
 
 struct blkdev_dio {
-       struct kiocb            *iocb;
-       struct task_struct      *waiter;
+       union {
+               struct kiocb            *iocb;
+               struct task_struct      *waiter;
+       };
        size_t                  size;
        atomic_t                ref;
        bool                    multi_bio : 1;
        bool                    should_dirty : 1;
+       bool                    is_sync : 1;
        struct bio              bio;
 };
 
@@ -286,13 +289,13 @@ static struct bio_set *blkdev_dio_pool __read_mostly;
 static void blkdev_bio_end_io(struct bio *bio)
 {
        struct blkdev_dio *dio = bio->bi_private;
-       struct kiocb *iocb = dio->iocb;
 
        if (dio->multi_bio && !atomic_dec_and_test(&dio->ref)) {
                if (bio->bi_error && !dio->bio.bi_error)
                        dio->bio.bi_error = bio->bi_error;
        } else {
-               if (iocb) {
+               if (!dio->is_sync) {
+                       struct kiocb *iocb = dio->iocb;
                        ssize_t ret = dio->bio.bi_error;
 
                        if (likely(!ret)) {
@@ -332,7 +335,6 @@ __blkdev_direct_IO(struct kiocb *iocb, struct iov_iter *iter, int nr_pages)
        struct blkdev_dio *dio;
        struct bio *bio;
        bool is_read = (iov_iter_rw(iter) == READ);
-       bool is_sync = is_sync_kiocb(iocb);
        loff_t pos = iocb->ki_pos;
        blk_qc_t qc = BLK_QC_T_NONE;
        int ret;
@@ -344,8 +346,12 @@ __blkdev_direct_IO(struct kiocb *iocb, struct iov_iter *iter, int nr_pages)
        bio_get(bio); /* extra ref for the completion handler */
 
        dio = container_of(bio, struct blkdev_dio, bio);
-       dio->iocb = is_sync ? NULL : iocb;
-       dio->waiter = current;
+       dio->is_sync = is_sync_kiocb(iocb);
+       if (dio->is_sync)
+               dio->waiter = current;
+       else
+               dio->iocb = iocb;
+
        dio->size = 0;
        dio->multi_bio = false;
        dio->should_dirty = is_read && (iter->type == ITER_IOVEC);
@@ -392,7 +398,7 @@ __blkdev_direct_IO(struct kiocb *iocb, struct iov_iter *iter, int nr_pages)
                bio = bio_alloc(GFP_KERNEL, nr_pages);
        }
 
-       if (!is_sync)
+       if (!dio->is_sync)
                return -EIOCBQUEUED;
 
        for (;;) {