2023-08-08 02:40:24

by Miaohe Lin

Subject: [PATCH] mm/page_alloc: remove unneeded current_order check

current_order is guaranteed to '>=' min_order while min_order always '>='
order. So current_order must be '>=' order.

Signed-off-by: Miaohe Lin <[email protected]>
---
mm/page_alloc.c | 3 +--
1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 96b7c1a7d1f2..d37ec87515d0 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -2072,8 +2072,7 @@ __rmqueue_fallback(struct zone *zone, int order, int start_migratetype,
* allocation falls back into a different pageblock than this
* one, it won't cause permanent fragmentation.
*/
- if (!can_steal && start_migratetype == MIGRATE_MOVABLE
- && current_order > order)
+ if (!can_steal && start_migratetype == MIGRATE_MOVABLE)
goto find_smallest;

goto do_steal;
--
2.33.0

2023-08-08 19:46:17

by Hugo Villeneuve

Subject: Re: [PATCH] mm/page_alloc: remove unneeded current_order check

On Tue, 8 Aug 2023 10:05:55 +0800
Miaohe Lin <[email protected]> wrote:

> current_order is guaranteed to '>=' min_order while min_order always '>='
> order. So current_order must be '>=' order.
>
> Signed-off-by: Miaohe Lin <[email protected]>
> ---
> mm/page_alloc.c | 3 +--
> 1 file changed, 1 insertion(+), 2 deletions(-)
>
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 96b7c1a7d1f2..d37ec87515d0 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -2072,8 +2072,7 @@ __rmqueue_fallback(struct zone *zone, int order, int start_migratetype,
> * allocation falls back into a different pageblock than this
> * one, it won't cause permanent fragmentation.
> */
> - if (!can_steal && start_migratetype == MIGRATE_MOVABLE
> - && current_order > order)
> + if (!can_steal && start_migratetype == MIGRATE_MOVABLE)
> goto find_smallest;

Hi,
if my analysis is correct, min_order can be initialized to the value of
order before the loop begins.

In that case, in the last loop iteration, current_order will be
equal to min_order and also to order. The condition 'current_order >
order' will evaluate to false, and the 'if' block should not be
executed?

Hugo.

2023-08-08 20:29:11

by Miaohe Lin

Subject: Re: [PATCH] mm/page_alloc: remove unneeded current_order check

On 2023/8/8 20:16, Hugo Villeneuve wrote:
> On Tue, 8 Aug 2023 10:05:55 +0800
> Miaohe Lin <[email protected]> wrote:
>
>> current_order is guaranteed to '>=' min_order while min_order always '>='
>> order. So current_order must be '>=' order.
>>
>> Signed-off-by: Miaohe Lin <[email protected]>
>> ---
>> mm/page_alloc.c | 3 +--
>> 1 file changed, 1 insertion(+), 2 deletions(-)
>>
>> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
>> index 96b7c1a7d1f2..d37ec87515d0 100644
>> --- a/mm/page_alloc.c
>> +++ b/mm/page_alloc.c
>> @@ -2072,8 +2072,7 @@ __rmqueue_fallback(struct zone *zone, int order, int start_migratetype,
>> * allocation falls back into a different pageblock than this
>> * one, it won't cause permanent fragmentation.
>> */
>> - if (!can_steal && start_migratetype == MIGRATE_MOVABLE
>> - && current_order > order)
>> + if (!can_steal && start_migratetype == MIGRATE_MOVABLE)
>> goto find_smallest;
>
> Hi,
> if my analysis is correct, min_order can be initialized to the value of
> order before the loop begins.
>
> In that case, in the last loop iteration, current_order will be
> equal to min_order and also to order. The condition 'current_order >
> order' will evaluate to false, and the 'if' block should not be
> executed?

Oh, that's my mistake. Thanks for pointing this out. Will drop this patch.

Thanks!