[PATCH 0/3] md: code cleanups

[PATCH 0/3] md: code cleanups

[Pankaj Gupta]

From: Pankaj Gupta <pankaj.gupta@cloud.ionos.com>

This patch series does some cleanups during my attempt to understand
the code. 

Pankaj Gupta (3):
  md: improve variable names in md_flush_request()
  md: add comments in md_flush_request()
  md: use current request time as base for ktime comparisons

 drivers/md/md.c | 12 ++++++++----
 drivers/md/md.h |  6 +++---
 2 files changed, 11 insertions(+), 7 deletions(-)

-- 
2.20.1

[PATCH 1/3] md: improve variable names in md_flush_request()

[Pankaj Gupta]

From: Pankaj Gupta <pankaj.gupta@cloud.ionos.com>

 This patch improves readability by using better variable names
 in flush request coalescing logic.

Signed-off-by: Pankaj Gupta <pankaj.gupta@cloud.ionos.com>
---
 drivers/md/md.c | 8 ++++----
 drivers/md/md.h | 6 +++---
 2 files changed, 7 insertions(+), 7 deletions(-)

diff --git a/drivers/md/md.c b/drivers/md/md.c
index 98bac4f304ae..167c80f98533 100644
--- a/drivers/md/md.c
+++ b/drivers/md/md.c
@@ -639,7 +639,7 @@ static void md_submit_flush_data(struct work_struct *ws)
 	 * could wait for this and below md_handle_request could wait for those
 	 * bios because of suspend check
 	 */
-	mddev->last_flush = mddev->start_flush;
+	mddev->prev_flush_start = mddev->start_flush;
 	mddev->flush_bio = NULL;
 	wake_up(&mddev->sb_wait);
 
@@ -660,13 +660,13 @@ static void md_submit_flush_data(struct work_struct *ws)
  */
 bool md_flush_request(struct mddev *mddev, struct bio *bio)
 {
-	ktime_t start = ktime_get_boottime();
+	ktime_t req_start = ktime_get_boottime();
 	spin_lock_irq(&mddev->lock);
 	wait_event_lock_irq(mddev->sb_wait,
 			    !mddev->flush_bio ||
-			    ktime_after(mddev->last_flush, start),
+			    ktime_after(mddev->prev_flush_start, req_start),
 			    mddev->lock);
-	if (!ktime_after(mddev->last_flush, start)) {
+	if (!ktime_after(mddev->prev_flush_start, req_start)) {
 		WARN_ON(mddev->flush_bio);
 		mddev->flush_bio = bio;
 		bio = NULL;
diff --git a/drivers/md/md.h b/drivers/md/md.h
index ccfb69868c2e..2292c847f9dd 100644
--- a/drivers/md/md.h
+++ b/drivers/md/md.h
@@ -495,9 +495,9 @@ struct mddev {
 	 */
 	struct bio *flush_bio;
 	atomic_t flush_pending;
-	ktime_t start_flush, last_flush; /* last_flush is when the last completed
-					  * flush was started.
-					  */
+	ktime_t start_flush, prev_flush_start; /* prev_flush_start is when the previous completed
+						* flush was started.
+						*/
 	struct work_struct flush_work;
 	struct work_struct event_work;	/* used by dm to report failure event */
 	mempool_t *serial_info_pool;
-- 
2.20.1

Re: [PATCH 1/3] md: improve variable names in md_flush_request()

[Paul Menzel]

Dear Pankaj,


Thank you for the cleanups.

Am 11.11.20 um 06:16 schrieb Pankaj Gupta:
> From: Pankaj Gupta <pankaj.gupta@cloud.ionos.com>
> 
>   This patch improves readability by using better variable names
>   in flush request coalescing logic.

Please do not indent the commit message.

> Signed-off-by: Pankaj Gupta <pankaj.gupta@cloud.ionos.com>
> ---
>   drivers/md/md.c | 8 ++++----
>   drivers/md/md.h | 6 +++---
>   2 files changed, 7 insertions(+), 7 deletions(-)
> 
> diff --git a/drivers/md/md.c b/drivers/md/md.c
> index 98bac4f304ae..167c80f98533 100644
> --- a/drivers/md/md.c
> +++ b/drivers/md/md.c
> @@ -639,7 +639,7 @@ static void md_submit_flush_data(struct work_struct *ws)
>   	 * could wait for this and below md_handle_request could wait for those
>   	 * bios because of suspend check
>   	 */
> -	mddev->last_flush = mddev->start_flush;
> +	mddev->prev_flush_start = mddev->start_flush;
>   	mddev->flush_bio = NULL;
>   	wake_up(&mddev->sb_wait);
>   
> @@ -660,13 +660,13 @@ static void md_submit_flush_data(struct work_struct *ws)
>    */
>   bool md_flush_request(struct mddev *mddev, struct bio *bio)
>   {
> -	ktime_t start = ktime_get_boottime();
> +	ktime_t req_start = ktime_get_boottime();
>   	spin_lock_irq(&mddev->lock);
>   	wait_event_lock_irq(mddev->sb_wait,
>   			    !mddev->flush_bio ||
> -			    ktime_after(mddev->last_flush, start),
> +			    ktime_after(mddev->prev_flush_start, req_start),
>   			    mddev->lock);
> -	if (!ktime_after(mddev->last_flush, start)) {
> +	if (!ktime_after(mddev->prev_flush_start, req_start)) {
>   		WARN_ON(mddev->flush_bio);
>   		mddev->flush_bio = bio;
>   		bio = NULL;
> diff --git a/drivers/md/md.h b/drivers/md/md.h
> index ccfb69868c2e..2292c847f9dd 100644
> --- a/drivers/md/md.h
> +++ b/drivers/md/md.h
> @@ -495,9 +495,9 @@ struct mddev {
>   	 */
>   	struct bio *flush_bio;
>   	atomic_t flush_pending;
> -	ktime_t start_flush, last_flush; /* last_flush is when the last completed
> -					  * flush was started.
> -					  */
> +	ktime_t start_flush, prev_flush_start; /* prev_flush_start is when the previous completed
> +						* flush was started.
> +						*/

With the new variable name, the comment could even be removed. ;-)

>   	struct work_struct flush_work;
>   	struct work_struct event_work;	/* used by dm to report failure event */
>   	mempool_t *serial_info_pool;

Reviewed-by: Paul Menzel <pmenzel@molgen.mpg.de>


Kind regards,

Paul

Re: [PATCH 1/3] md: improve variable names in md_flush_request()

[Pankaj Gupta]

Hi Paul,

> >   This patch improves readability by using better variable names
> >   in flush request coalescing logic.
>
> Please do not indent the commit message.

o.k

>
> > Signed-off-by: Pankaj Gupta <pankaj.gupta@cloud.ionos.com>
> > ---
> >   drivers/md/md.c | 8 ++++----
> >   drivers/md/md.h | 6 +++---
> >   2 files changed, 7 insertions(+), 7 deletions(-)
> >
> > diff --git a/drivers/md/md.c b/drivers/md/md.c
> > index 98bac4f304ae..167c80f98533 100644
> > --- a/drivers/md/md.c
> > +++ b/drivers/md/md.c
> > @@ -639,7 +639,7 @@ static void md_submit_flush_data(struct work_struct *ws)
> >        * could wait for this and below md_handle_request could wait for those
> >        * bios because of suspend check
> >        */
> > -     mddev->last_flush = mddev->start_flush;
> > +     mddev->prev_flush_start = mddev->start_flush;
> >       mddev->flush_bio = NULL;
> >       wake_up(&mddev->sb_wait);
> >
> > @@ -660,13 +660,13 @@ static void md_submit_flush_data(struct work_struct *ws)
> >    */
> >   bool md_flush_request(struct mddev *mddev, struct bio *bio)
> >   {
> > -     ktime_t start = ktime_get_boottime();
> > +     ktime_t req_start = ktime_get_boottime();
> >       spin_lock_irq(&mddev->lock);
> >       wait_event_lock_irq(mddev->sb_wait,
> >                           !mddev->flush_bio ||
> > -                         ktime_after(mddev->last_flush, start),
> > +                         ktime_after(mddev->prev_flush_start, req_start),
> >                           mddev->lock);
> > -     if (!ktime_after(mddev->last_flush, start)) {
> > +     if (!ktime_after(mddev->prev_flush_start, req_start)) {
> >               WARN_ON(mddev->flush_bio);
> >               mddev->flush_bio = bio;
> >               bio = NULL;
> > diff --git a/drivers/md/md.h b/drivers/md/md.h
> > index ccfb69868c2e..2292c847f9dd 100644
> > --- a/drivers/md/md.h
> > +++ b/drivers/md/md.h
> > @@ -495,9 +495,9 @@ struct mddev {
> >        */
> >       struct bio *flush_bio;
> >       atomic_t flush_pending;
> > -     ktime_t start_flush, last_flush; /* last_flush is when the last completed
> > -                                       * flush was started.
> > -                                       */
> > +     ktime_t start_flush, prev_flush_start; /* prev_flush_start is when the previous completed
> > +                                             * flush was started.
> > +                                             */
>
> With the new variable name, the comment could even be removed. ;-)
>
> >       struct work_struct flush_work;
> >       struct work_struct event_work;  /* used by dm to report failure event */
> >       mempool_t *serial_info_pool;
>
> Reviewed-by: Paul Menzel <pmenzel@molgen.mpg.de>

Thanks,
Pankaj
>
>
> Kind regards,
>
> Paul

[PATCH 2/3] md: add comments in md_flush_request()

[Pankaj Gupta]

From: Pankaj Gupta <pankaj.gupta@cloud.ionos.com>

 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>
---
 drivers/md/md.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/drivers/md/md.c b/drivers/md/md.c
index 167c80f98533..a330e61876e0 100644
--- 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;
-- 
2.20.1

[PATCH 3/3] md: use current request time as base for ktime comparisons

[Pankaj Gupta]

From: Pankaj Gupta <pankaj.gupta@cloud.ionos.com>

Request coalescing logic uses 'prev_flush_start' as base to
compare the current request start time. 'prev_flush_start' is
updated in other context.

This patch changes this by using ktime comparison base to
'req_start' for better readability of code.

Signed-off-by: Pankaj Gupta <pankaj.gupta@cloud.ionos.com>
---
 drivers/md/md.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/md/md.c b/drivers/md/md.c
index a330e61876e0..217b1e3312cb 100644
--- a/drivers/md/md.c
+++ b/drivers/md/md.c
@@ -667,10 +667,10 @@ bool md_flush_request(struct mddev *mddev, struct bio *bio)
 	 */
 	wait_event_lock_irq(mddev->sb_wait,
 			    !mddev->flush_bio ||
-			    ktime_after(mddev->prev_flush_start, req_start),
+			    ktime_before(req_start, mddev->prev_flush_start),
 			    mddev->lock);
 	/* new request after previous flush is completed */
-	if (!ktime_after(mddev->prev_flush_start, req_start)) {
+	if (ktime_after(req_start, mddev->prev_flush_start)) {
 		WARN_ON(mddev->flush_bio);
 		mddev->flush_bio = bio;
 		bio = NULL;
-- 
2.20.1

Re: [PATCH 0/3] md: code cleanups

[Song Liu]

On Tue, Nov 10, 2020 at 9:17 PM Pankaj Gupta
<pankaj.gupta.linux@gmail.com> wrote:
>
> From: Pankaj Gupta <pankaj.gupta@cloud.ionos.com>
>
> This patch series does some cleanups during my attempt to understand
> the code.
>
> Pankaj Gupta (3):
>   md: improve variable names in md_flush_request()
>   md: add comments in md_flush_request()
>   md: use current request time as base for ktime comparisons

Thanks for the clean up. Applied to md-next.