linux-kernel - Re: [Patch v3 7/7] mm/hugetlb: take the free hpage during the iteration directly

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Date:   Mon, 31 Aug 2020 16:06:54 -0700
From:   Mike Kravetz <mike.kravetz@...cle.com>
To:     Wei Yang <richard.weiyang@...ux.alibaba.com>,
        akpm@...ux-foundation.org
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org, bhe@...hat.com
Subject: Re: [Patch v3 7/7] mm/hugetlb: take the free hpage during the
 iteration directly

On 8/30/20 7:23 PM, Wei Yang wrote:
> Function dequeue_huge_page_node_exact() iterates the free list and
> return the first valid free hpage.
> 
> 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 | 20 ++++++++------------
>  1 file changed, 8 insertions(+), 12 deletions(-)
> 
> diff --git a/mm/hugetlb.c b/mm/hugetlb.c
> index 7b3357c1dcec..709be7ab65af 100644
> --- a/mm/hugetlb.c
> +++ b/mm/hugetlb.c
> @@ -1040,21 +1040,17 @@ static struct page *dequeue_huge_page_node_exact(struct hstate *h, int nid)
>  		if (nocma && is_migrate_cma_page(page))
>  			continue;
>  
> -		if (!PageHWPoison(page))
> +		if (PageHWPoison(page))
>  			break;

Previously, when encountering a PageHWPoison(page) the loop would continue
and check the next page in the list.  It now breaks the loop and returns
NULL.  Is not this a change in behavior?  Perhaps you want to change that
break to a continue.  Or, restructure in some other way.
-- 
Mike Kravetz

> +
> +		list_move(&page->lru, &h->hugepage_activelist);
> +		set_page_refcounted(page);
> +		h->free_huge_pages--;
> +		h->free_huge_pages_node[nid]--;
> +		return page;
>  	}
>  
> -	/*
> -	 * if 'non-isolated free hugepage' not found on the list,
> -	 * the allocation fails.
> -	 */
> -	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;
> +	return NULL;
>  }
>  
>  static struct page *dequeue_huge_page_nodemask(struct hstate *h, gfp_t gfp_mask, int nid,
>