md: add comments in md_flush_request()

Request coalescing logic is dependent on flush time update in other
context. This patch adds comments to understand the code flow better.

Signed-off-by: Pankaj Gupta <pankaj.gupta@cloud.ionos.com>
Signed-off-by: Song Liu <songliubraving@fb.com>

diff --git a/drivers/md/md.c b/drivers/md/md.c
index 3992e8c..a0998ad 100644 (file)
--- a/drivers/md/md.c
+++ b/drivers/md/md.c
@@ -662,10 +662,14 @@ bool md_flush_request(struct mddev *mddev, struct bio *bio)
 {
        ktime_t req_start = ktime_get_boottime();
        spin_lock_irq(&mddev->lock);
+       /* flush requests wait until ongoing flush completes,
+        * hence coalescing all the pending requests.
+        */
        wait_event_lock_irq(mddev->sb_wait,
                            !mddev->flush_bio ||
                            ktime_after(mddev->prev_flush_start, req_start),
                            mddev->lock);
+       /* new request after previous flush is completed */
        if (!ktime_after(mddev->prev_flush_start, req_start)) {
                WARN_ON(mddev->flush_bio);
                mddev->flush_bio = bio;