linux-kernel - Re: [PATCH v0] mm/page_alloc: Cleanup for __del_page_from_free

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Message-ID: <6fa0e2e3-045e-446f-8ef3-955711b6aa82@suse.cz>
Date: Tue, 30 Sep 2025 15:55:26 +0200
From: Vlastimil Babka <vbabka@...e.cz>
To: zhongjinji <zhongjinji@...or.com>, akpm@...ux-foundation.org
Cc: surenb@...gle.com, mhocko@...e.com, jackmanb@...gle.com,
 hannes@...xchg.org, ziy@...dia.com, linux-mm@...ck.org,
 linux-kernel@...r.kernel.org, liulu.liu@...or.com, feng.han@...or.com
Subject: Re: [PATCH v0] mm/page_alloc: Cleanup for __del_page_from_free_list()

On 9/25/25 10:50, zhongjinji wrote:
> It is unnecessary to set page->private in __del_page_from_free_list().
> 
> If the page is about to be allocated, page->private will be cleared by
> post_alloc_hook() before the page is handed out. If the page is expanded
> or merged, page->private will be reset by set_buddy_order, and no one
> will retrieve the page's buddy_order without the PageBuddy flag being set.
> If the page is isolated, it will also reset page->private when it
> succeeds.

Seems correct.

> Since __del_page_from_free_list() is a hot path in the kernel, it would be
> better to remove the unnecessary set_page_private().
> 
> Signed-off-by: zhongjinji <zhongjinji@...or.com>

Reviewed-by: Vlastimil Babka <vbabka@...e.cz>

> ---
>  mm/page_alloc.c | 1 -
>  1 file changed, 1 deletion(-)
> 
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index d1d037f97c5f..1999eb7e7c14 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -868,7 +868,6 @@ static inline void __del_page_from_free_list(struct page *page, struct zone *zon
>  
>  	list_del(&page->buddy_list);
>  	__ClearPageBuddy(page);
> -	set_page_private(page, 0);
>  	zone->free_area[order].nr_free--;
>  
>  	if (order >= pageblock_order && !is_migrate_isolate(migratetype))