linux-kernel - Re: [PATCH] mm/page_alloc: remove unneeded current

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Date:   Tue, 8 Aug 2023 08:16:51 -0400
From:   Hugo Villeneuve <hugo@...ovil.com>
To:     Miaohe Lin <linmiaohe@...wei.com>
Cc:     <akpm@...ux-foundation.org>, <linux-mm@...ck.org>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] mm/page_alloc: remove unneeded current_order check

On Tue, 8 Aug 2023 10:05:55 +0800
Miaohe Lin <linmiaohe@...wei.com> wrote:

> current_order is guaranteed to '>=' min_order while min_order always '>='
> order. So current_order must be '>=' order.
> 
> Signed-off-by: Miaohe Lin <linmiaohe@...wei.com>
> ---
>  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.