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[PATCH] mm: remove a redundant condition in the for loop

Started byHao Lee <haolee.swjtu@gmail.com>
First post2017-06-19 16:00 +0200
Last post2017-06-19 22:30 +0200
Articles 4 — 3 participants

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  [PATCH] mm: remove a redundant condition in the for loop Hao Lee <haolee.swjtu@gmail.com> - 2017-06-19 16:00 +0200
    Re: [PATCH] mm: remove a redundant condition in the for loop Vlastimil Babka <vbabka@suse.cz> - 2017-06-19 16:20 +0200
      Re: [PATCH] mm: remove a redundant condition in the for loop Rasmus Villemoes <linux@rasmusvillemoes.dk> - 2017-06-19 21:10 +0200
        Re: [PATCH] mm: remove a redundant condition in the for loop Vlastimil Babka <vbabka@suse.cz> - 2017-06-19 22:30 +0200

#1669081 — [PATCH] mm: remove a redundant condition in the for loop

FromHao Lee <haolee.swjtu@gmail.com>
Date2017-06-19 16:00 +0200
Subject[PATCH] mm: remove a redundant condition in the for loop
Message-ID<tU5nI-3mQ-1@gated-at.bofh.it>
The variable current_order decreases from MAX_ORDER-1 to order, so the
condition current_order <= MAX_ORDER-1 is always true.

Signed-off-by: Hao Lee <haolee.swjtu@gmail.com>
---
 mm/page_alloc.c | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 2302f25..9120c2b 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -2215,9 +2215,8 @@ __rmqueue_fallback(struct zone *zone, unsigned int order, int start_migratetype)
 	bool can_steal;
 
 	/* Find the largest possible block of pages in the other list */
-	for (current_order = MAX_ORDER-1;
-				current_order >= order && current_order <= MAX_ORDER-1;
-				--current_order) {
+	for (current_order = MAX_ORDER-1; current_order >= order;
+							--current_order) {
 		area = &(zone->free_area[current_order]);
 		fallback_mt = find_suitable_fallback(area, current_order,
 				start_migratetype, false, &can_steal);
-- 
2.9.3

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#1669100

FromVlastimil Babka <vbabka@suse.cz>
Date2017-06-19 16:20 +0200
Message-ID<tU5H3-3IR-9@gated-at.bofh.it>
In reply to#1669081
On 06/19/2017 03:54 PM, Hao Lee wrote:
> The variable current_order decreases from MAX_ORDER-1 to order, so the
> condition current_order <= MAX_ORDER-1 is always true.
> 
> Signed-off-by: Hao Lee <haolee.swjtu@gmail.com>

Sounds right.

Acked-by: Vlastimil Babka <vbabka@suse.cz>

> ---
>  mm/page_alloc.c | 5 ++---
>  1 file changed, 2 insertions(+), 3 deletions(-)
> 
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 2302f25..9120c2b 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -2215,9 +2215,8 @@ __rmqueue_fallback(struct zone *zone, unsigned int order, int start_migratetype)
>  	bool can_steal;
>  
>  	/* Find the largest possible block of pages in the other list */
> -	for (current_order = MAX_ORDER-1;
> -				current_order >= order && current_order <= MAX_ORDER-1;
> -				--current_order) {
> +	for (current_order = MAX_ORDER-1; current_order >= order;
> +							--current_order) {
>  		area = &(zone->free_area[current_order]);
>  		fallback_mt = find_suitable_fallback(area, current_order,
>  				start_migratetype, false, &can_steal);
>

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#1669713

FromRasmus Villemoes <linux@rasmusvillemoes.dk>
Date2017-06-19 21:10 +0200
Message-ID<tUadH-6Iy-3@gated-at.bofh.it>
In reply to#1669100
On Mon, Jun 19 2017, Vlastimil Babka <vbabka@suse.cz> wrote:

> On 06/19/2017 03:54 PM, Hao Lee wrote:
>> The variable current_order decreases from MAX_ORDER-1 to order, so the
>> condition current_order <= MAX_ORDER-1 is always true.
>> 
>> Signed-off-by: Hao Lee <haolee.swjtu@gmail.com>
>
> Sounds right.
>
> Acked-by: Vlastimil Babka <vbabka@suse.cz>

current_order and order are both unsigned, and if order==0,
current_order >= order is always true, and we may decrement
current_order past 0 making it UINT_MAX... A comment would be in order,
though.

>> ---
>>  mm/page_alloc.c | 5 ++---
>>  1 file changed, 2 insertions(+), 3 deletions(-)
>> 
>> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
>> index 2302f25..9120c2b 100644
>> --- a/mm/page_alloc.c
>> +++ b/mm/page_alloc.c
>> @@ -2215,9 +2215,8 @@ __rmqueue_fallback(struct zone *zone, unsigned int order, int start_migratetype)
>>  	bool can_steal;
>>  
>>  	/* Find the largest possible block of pages in the other list */
>> -	for (current_order = MAX_ORDER-1;
>> -				current_order >= order && current_order <= MAX_ORDER-1;
>> -				--current_order) {
>> +	for (current_order = MAX_ORDER-1; current_order >= order;
>> +							--current_order) {
>>  		area = &(zone->free_area[current_order]);
>>  		fallback_mt = find_suitable_fallback(area, current_order,
>>  				start_migratetype, false, &can_steal);
>>

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#1669907

FromVlastimil Babka <vbabka@suse.cz>
Date2017-06-19 22:30 +0200
Message-ID<tUbt7-7sP-5@gated-at.bofh.it>
In reply to#1669713
On 06/19/2017 09:05 PM, Rasmus Villemoes wrote:
> On Mon, Jun 19 2017, Vlastimil Babka <vbabka@suse.cz> wrote:
> 
>> On 06/19/2017 03:54 PM, Hao Lee wrote:
>>> The variable current_order decreases from MAX_ORDER-1 to order, so the
>>> condition current_order <= MAX_ORDER-1 is always true.
>>>
>>> Signed-off-by: Hao Lee <haolee.swjtu@gmail.com>
>>
>> Sounds right.
>>
>> Acked-by: Vlastimil Babka <vbabka@suse.cz>
> 
> current_order and order are both unsigned, and if order==0,
> current_order >= order is always true, and we may decrement
> current_order past 0 making it UINT_MAX... A comment would be in order,
> though.

Doh, right. Thanks.

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