linux-kernel - Re: [PATCH v3 2/5] mm/huge_memory.c: use page->deferred

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Message-ID: <YJsNRtg5IcMY7V/F@casper.infradead.org>
Date:   Wed, 12 May 2021 00:03:34 +0100
From:   Matthew Wilcox <willy@...radead.org>
To:     Miaohe Lin <linmiaohe@...wei.com>
Cc:     akpm@...ux-foundation.org, ziy@...dia.com,
        william.kucharski@...cle.com, yang.shi@...ux.alibaba.com,
        aneesh.kumar@...ux.ibm.com, rcampbell@...dia.com,
        songliubraving@...com, kirill.shutemov@...ux.intel.com,
        riel@...riel.com, hannes@...xchg.org, minchan@...nel.org,
        hughd@...gle.com, adobriyan@...il.com,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH v3 2/5] mm/huge_memory.c: use page->deferred_list

On Tue, May 11, 2021 at 09:48:54PM +0800, Miaohe Lin wrote:
> Now that we can represent the location of ->deferred_list instead of
> ->mapping + ->index, make use of it to improve readability.
> 
> Reviewed-by: Yang Shi <shy828301@...il.com>
> Reviewed-by: David Hildenbrand <david@...hat.com>
> Signed-off-by: Miaohe Lin <linmiaohe@...wei.com>
> ---
>  mm/huge_memory.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/mm/huge_memory.c b/mm/huge_memory.c
> index 63ed6b25deaa..76ca1eb2a223 100644
> --- a/mm/huge_memory.c
> +++ b/mm/huge_memory.c
> @@ -2868,7 +2868,7 @@ static unsigned long deferred_split_scan(struct shrinker *shrink,
>  	spin_lock_irqsave(&ds_queue->split_queue_lock, flags);
>  	/* Take pin on all head pages to avoid freeing them under us */
>  	list_for_each_safe(pos, next, &ds_queue->split_queue) {
> -		page = list_entry((void *)pos, struct page, mapping);
> +		page = list_entry((void *)pos, struct page, deferred_list);
>  		page = compound_head(page);

This is an equivalent transformation, but it doesn't really go far
enough.  I think you want something like this:

	struct page *page, *next;

	list_for_each_entry_safe(page, next, &ds_queue->split_queue,
							deferred_list) {
		struct page *head = page - 1;
		... then use head throughout ...
	}