* [PATCH] mm/vmscan.c: Clean code by removing unnecessary assignment
@ 2020-02-29 21:40 mateusznosek0
2020-03-01 0:11 ` Matthew Wilcox
` (2 more replies)
0 siblings, 3 replies; 7+ messages in thread
From: mateusznosek0 @ 2020-02-29 21:40 UTC (permalink / raw)
To: linux-mm, linux-kernel; +Cc: Mateusz Nosek, akpm
From: Mateusz Nosek <mateusznosek0@gmail.com>
Previously 0 was assigned to variable 'lruvec_size',
but the variable was never read later.
So the assignment can be removed.
Signed-off-by: Mateusz Nosek <mateusznosek0@gmail.com>
---
mm/vmscan.c | 4 +---
1 file changed, 1 insertion(+), 3 deletions(-)
diff --git a/mm/vmscan.c b/mm/vmscan.c
index f14c8c6069a6..a605ff36f126 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -2427,10 +2427,8 @@ static void get_scan_count(struct lruvec *lruvec, struct scan_control *sc,
case SCAN_FILE:
case SCAN_ANON:
/* Scan one type exclusively */
- if ((scan_balance == SCAN_FILE) != file) {
- lruvec_size = 0;
+ if ((scan_balance == SCAN_FILE) != file)
scan = 0;
- }
break;
default:
/* Look ma, no brain */
--
2.17.1
^ permalink raw reply related [flat|nested] 7+ messages in thread
* Re: [PATCH] mm/vmscan.c: Clean code by removing unnecessary assignment
2020-02-29 21:40 [PATCH] mm/vmscan.c: Clean code by removing unnecessary assignment mateusznosek0
@ 2020-03-01 0:11 ` Matthew Wilcox
2020-03-02 13:54 ` Wei Yang
2020-03-03 8:59 ` David Hildenbrand
2 siblings, 0 replies; 7+ messages in thread
From: Matthew Wilcox @ 2020-03-01 0:11 UTC (permalink / raw)
To: mateusznosek0; +Cc: linux-mm, linux-kernel, akpm
On Sat, Feb 29, 2020 at 10:40:22PM +0100, mateusznosek0@gmail.com wrote:
> From: Mateusz Nosek <mateusznosek0@gmail.com>
>
> Previously 0 was assigned to variable 'lruvec_size',
> but the variable was never read later.
> So the assignment can be removed.
>
> Signed-off-by: Mateusz Nosek <mateusznosek0@gmail.com>
It _was_ used, until commit f87bccde6a7dd1bdb219a4045e8ac111590c9314
which removed lru_pages. So this is just a left-over, and I agree it's
now superfluous.
Reviewed-by: Matthew Wilcox (Oracle) <willy@infradead.org>
^ permalink raw reply [flat|nested] 7+ messages in thread
* Re: [PATCH] mm/vmscan.c: Clean code by removing unnecessary assignment
2020-02-29 21:40 [PATCH] mm/vmscan.c: Clean code by removing unnecessary assignment mateusznosek0
2020-03-01 0:11 ` Matthew Wilcox
@ 2020-03-02 13:54 ` Wei Yang
2020-03-03 8:59 ` David Hildenbrand
2 siblings, 0 replies; 7+ messages in thread
From: Wei Yang @ 2020-03-02 13:54 UTC (permalink / raw)
To: mateusznosek0; +Cc: linux-mm, linux-kernel, akpm
On Sat, Feb 29, 2020 at 10:40:22PM +0100, mateusznosek0@gmail.com wrote:
>From: Mateusz Nosek <mateusznosek0@gmail.com>
>
>Previously 0 was assigned to variable 'lruvec_size',
>but the variable was never read later.
>So the assignment can be removed.
>
>Signed-off-by: Mateusz Nosek <mateusznosek0@gmail.com>
Reviewed-by: Wei Yang <richard.weiyang@gmail.com>
--
Wei Yang
Help you, Help me
^ permalink raw reply [flat|nested] 7+ messages in thread
* Re: [PATCH] mm/vmscan.c: Clean code by removing unnecessary assignment
2020-02-29 21:40 [PATCH] mm/vmscan.c: Clean code by removing unnecessary assignment mateusznosek0
2020-03-01 0:11 ` Matthew Wilcox
2020-03-02 13:54 ` Wei Yang
@ 2020-03-03 8:59 ` David Hildenbrand
2 siblings, 0 replies; 7+ messages in thread
From: David Hildenbrand @ 2020-03-03 8:59 UTC (permalink / raw)
To: mateusznosek0, linux-mm, linux-kernel; +Cc: akpm
On 29.02.20 22:40, mateusznosek0@gmail.com wrote:
> From: Mateusz Nosek <mateusznosek0@gmail.com>
>
> Previously 0 was assigned to variable 'lruvec_size',
> but the variable was never read later.
> So the assignment can be removed.
>
> Signed-off-by: Mateusz Nosek <mateusznosek0@gmail.com>
> ---
> mm/vmscan.c | 4 +---
> 1 file changed, 1 insertion(+), 3 deletions(-)
>
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index f14c8c6069a6..a605ff36f126 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -2427,10 +2427,8 @@ static void get_scan_count(struct lruvec *lruvec, struct scan_control *sc,
> case SCAN_FILE:
> case SCAN_ANON:
> /* Scan one type exclusively */
> - if ((scan_balance == SCAN_FILE) != file) {
> - lruvec_size = 0;
> + if ((scan_balance == SCAN_FILE) != file)
> scan = 0;
> - }
> break;
> default:
> /* Look ma, no brain */
>
Reviewed-by: David Hildenbrand <david@redhat.com>
--
Thanks,
David / dhildenb
^ permalink raw reply [flat|nested] 7+ messages in thread
* Re: [PATCH] mm/vmscan.c: Clean code by removing unnecessary assignment
2020-03-19 17:13 ` Michal Hocko
@ 2020-03-20 15:55 ` Johannes Weiner
0 siblings, 0 replies; 7+ messages in thread
From: Johannes Weiner @ 2020-03-20 15:55 UTC (permalink / raw)
To: Michal Hocko; +Cc: mateusznosek0, linux-mm, linux-kernel, akpm
On Thu, Mar 19, 2020 at 06:13:34PM +0100, Michal Hocko wrote:
> It is usually preferable to Cc author of the code (added Johannes)
>
> On Thu 19-03-20 17:59:38, mateusznosek0@gmail.com wrote:
> > From: Mateusz Nosek <mateusznosek0@gmail.com>
> >
> > Previously 0 was assigned to 'sc->skipped_deactivate'. It could happen only
> > if 'sc->skipped_deactivate' was 0 so the assignment is unnecessary and can
> > be removed.
>
> The above wording was a bit hard to understdand for me. I would go with
> "
> sc->memcg_low_skipped resets skipped_deactivate to 0 but this is not
> needed as this code path is never reachable with skipped_deactivate != 0
> due to previous sc->skipped_deactivate branch.
> "
Yeah that sounds good.
> > Signed-off-by: Mateusz Nosek <mateusznosek0@gmail.com>
>
> The patch is correct. I am not sure it results in a better code though.
> I will defer to Johannes here. I suspect he simply wanted to express
> that skipped_deactivate should be always reset when retrying the direct
> reclaim. After this patch this could be lost in future changes so the
> code would be more subtle. But I am only guessing here.
It's a valid concern, but I think in this case specifically we're very
unlikely to change the ordering here - violate memory.low before going
after active pages of unprotected cgroups.
I indeed just kept it stupid: reset everything, then retry. But it
appears that the unnecessary assignment trips people up and wastes
their time, so I'm in favor of removing it.
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
^ permalink raw reply [flat|nested] 7+ messages in thread
* Re: [PATCH] mm/vmscan.c: Clean code by removing unnecessary assignment
2020-03-19 16:59 mateusznosek0
@ 2020-03-19 17:13 ` Michal Hocko
2020-03-20 15:55 ` Johannes Weiner
0 siblings, 1 reply; 7+ messages in thread
From: Michal Hocko @ 2020-03-19 17:13 UTC (permalink / raw)
To: mateusznosek0; +Cc: linux-mm, linux-kernel, akpm, Johannes Weiner
It is usually preferable to Cc author of the code (added Johannes)
On Thu 19-03-20 17:59:38, mateusznosek0@gmail.com wrote:
> From: Mateusz Nosek <mateusznosek0@gmail.com>
>
> Previously 0 was assigned to 'sc->skipped_deactivate'. It could happen only
> if 'sc->skipped_deactivate' was 0 so the assignment is unnecessary and can
> be removed.
The above wording was a bit hard to understdand for me. I would go with
"
sc->memcg_low_skipped resets skipped_deactivate to 0 but this is not
needed as this code path is never reachable with skipped_deactivate != 0
due to previous sc->skipped_deactivate branch.
"
> Signed-off-by: Mateusz Nosek <mateusznosek0@gmail.com>
The patch is correct. I am not sure it results in a better code though.
I will defer to Johannes here. I suspect he simply wanted to express
that skipped_deactivate should be always reset when retrying the direct
reclaim. After this patch this could be lost in future changes so the
code would be more subtle. But I am only guessing here.
> ---
> mm/vmscan.c | 1 -
> 1 file changed, 1 deletion(-)
>
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index dca623db51c8..453ff2abcb58 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -3093,7 +3093,6 @@ static unsigned long do_try_to_free_pages(struct zonelist *zonelist,
> if (sc->memcg_low_skipped) {
> sc->priority = initial_priority;
> sc->force_deactivate = 0;
> - sc->skipped_deactivate = 0;
> sc->memcg_low_reclaim = 1;
> sc->memcg_low_skipped = 0;
> goto retry;
> --
> 2.17.1
--
Michal Hocko
SUSE Labs
^ permalink raw reply [flat|nested] 7+ messages in thread
* [PATCH] mm/vmscan.c: Clean code by removing unnecessary assignment
@ 2020-03-19 16:59 mateusznosek0
2020-03-19 17:13 ` Michal Hocko
0 siblings, 1 reply; 7+ messages in thread
From: mateusznosek0 @ 2020-03-19 16:59 UTC (permalink / raw)
To: linux-mm, linux-kernel; +Cc: Mateusz Nosek, akpm
From: Mateusz Nosek <mateusznosek0@gmail.com>
Previously 0 was assigned to 'sc->skipped_deactivate'. It could happen only
if 'sc->skipped_deactivate' was 0 so the assignment is unnecessary and can
be removed.
Signed-off-by: Mateusz Nosek <mateusznosek0@gmail.com>
---
mm/vmscan.c | 1 -
1 file changed, 1 deletion(-)
diff --git a/mm/vmscan.c b/mm/vmscan.c
index dca623db51c8..453ff2abcb58 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -3093,7 +3093,6 @@ static unsigned long do_try_to_free_pages(struct zonelist *zonelist,
if (sc->memcg_low_skipped) {
sc->priority = initial_priority;
sc->force_deactivate = 0;
- sc->skipped_deactivate = 0;
sc->memcg_low_reclaim = 1;
sc->memcg_low_skipped = 0;
goto retry;
--
2.17.1
^ permalink raw reply related [flat|nested] 7+ messages in thread
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2020-02-29 21:40 [PATCH] mm/vmscan.c: Clean code by removing unnecessary assignment mateusznosek0
2020-03-01 0:11 ` Matthew Wilcox
2020-03-02 13:54 ` Wei Yang
2020-03-03 8:59 ` David Hildenbrand
2020-03-19 16:59 mateusznosek0
2020-03-19 17:13 ` Michal Hocko
2020-03-20 15:55 ` Johannes Weiner
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