linux-kernel - Re: [PATCH 08/10] mm/hugetlb: return non-isolated page in the loop instead of break and check

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Date:   Fri, 7 Aug 2020 21:09:31 +0800
From:   Baoquan He <bhe@...hat.com>
To:     Wei Yang <richard.weiyang@...ux.alibaba.com>
Cc:     mike.kravetz@...cle.com, akpm@...ux-foundation.org,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 08/10] mm/hugetlb: return non-isolated page in the loop
 instead of break and check

On 08/07/20 at 05:12pm, Wei Yang wrote:
> Function dequeue_huge_page_node_exact() iterates the free list and
> return the first non-isolated one.
> 
> Instead of break and check the loop variant, we could return in the loop
> directly. This could reduce some redundant check.
> 
> Signed-off-by: Wei Yang <richard.weiyang@...ux.alibaba.com>
> ---
>  mm/hugetlb.c | 26 ++++++++++++--------------
>  1 file changed, 12 insertions(+), 14 deletions(-)
> 
> diff --git a/mm/hugetlb.c b/mm/hugetlb.c
> index b8e844911b5a..9473eb6800e9 100644
> --- a/mm/hugetlb.c
> +++ b/mm/hugetlb.c
> @@ -1035,20 +1035,18 @@ static struct page *dequeue_huge_page_node_exact(struct hstate *h, int nid)
>  {
>  	struct page *page;
>  
> -	list_for_each_entry(page, &h->hugepage_freelists[nid], lru)
> -		if (!PageHWPoison(page))
> -			break;

I don't see how it can reduce redundant check, just two different
styles.

> -	/*
> -	 * if 'non-isolated free hugepage' not found on the list,
> -	 * the allocation fails.

But the above code comment seems stale, it checks HWPoision page
directly, but not the old isolated page checking.

> -	 */
> -	if (&h->hugepage_freelists[nid] == &page->lru)
> -		return NULL;
> -	list_move(&page->lru, &h->hugepage_activelist);
> -	set_page_refcounted(page);
> -	h->free_huge_pages--;
> -	h->free_huge_pages_node[nid]--;
> -	return page;
> +	list_for_each_entry(page, &h->hugepage_freelists[nid], lru) {
> +		if (PageHWPoison(page))
> +			continue;
> +
> +		list_move(&page->lru, &h->hugepage_activelist);
> +		set_page_refcounted(page);
> +		h->free_huge_pages--;
> +		h->free_huge_pages_node[nid]--;
> +		return page;
> +	}
> +
> +	return NULL;
>  }
>  
>  static struct page *dequeue_huge_page_nodemask(struct hstate *h, gfp_t gfp_mask, int nid,
> -- 
> 2.20.1 (Apple Git-117)
> 
>