block: add polled wakeup task helper

If we're polling for IO on a device that doesn't use interrupts, then
IO completion loop (and wake of task) is done by submitting task itself.
If that is the case, then we don't need to enter the wake_up_process()
function, we can simply mark ourselves as TASK_RUNNING.

Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

diff --git a/fs/block_dev.c b/fs/block_dev.c
index c039abf..9fe5667 100644 (file)
--- a/fs/block_dev.c
+++ b/fs/block_dev.c
@@ -181,7 +181,7 @@ static void blkdev_bio_end_io_simple(struct bio *bio)
        struct task_struct *waiter = bio->bi_private;
 
        WRITE_ONCE(bio->bi_private, NULL);
-       wake_up_process(waiter);
+       blk_wake_io_task(waiter);
 }
 
 static ssize_t
@@ -305,7 +305,7 @@ static void blkdev_bio_end_io(struct bio *bio)
                        struct task_struct *waiter = dio->waiter;
 
                        WRITE_ONCE(dio->waiter, NULL);
-                       wake_up_process(waiter);
+                       blk_wake_io_task(waiter);
                }
        }
 

diff --git a/fs/iomap.c b/fs/iomap.c
index f61d13d..b0462b3 100644 (file)
--- a/fs/iomap.c
+++ b/fs/iomap.c
@@ -1525,7 +1525,7 @@ static void iomap_dio_bio_end_io(struct bio *bio)
                if (dio->wait_for_completion) {
                        struct task_struct *waiter = dio->submit.waiter;
                        WRITE_ONCE(dio->submit.waiter, NULL);
-                       wake_up_process(waiter);
+                       blk_wake_io_task(waiter);
                } else if (dio->flags & IOMAP_DIO_WRITE) {
                        struct inode *inode = file_inode(dio->iocb->ki_filp);
 

diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index 41aaa05..91c44f7 100644 (file)
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -1772,4 +1772,17 @@ static inline int blkdev_issue_flush(struct block_device *bdev, gfp_t gfp_mask,
 
 #endif /* CONFIG_BLOCK */
 
+static inline void blk_wake_io_task(struct task_struct *waiter)
+{
+       /*
+        * If we're polling, the task itself is doing the completions. For
+        * that case, we don't need to signal a wakeup, it's enough to just
+        * mark us as RUNNING.
+        */
+       if (waiter == current)
+               __set_current_state(TASK_RUNNING);
+       else
+               wake_up_process(waiter);
+}
+
 #endif

diff --git a/mm/page_io.c b/mm/page_io.c
index d4d1c89..57572ff 100644 (file)
--- a/mm/page_io.c
+++ b/mm/page_io.c
@@ -140,7 +140,7 @@ out:
        unlock_page(page);
        WRITE_ONCE(bio->bi_private, NULL);
        bio_put(bio);
-       wake_up_process(waiter);
+       blk_wake_io_task(waiter);
        put_task_struct(waiter);
 }