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

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Date:   Tue, 1 Sep 2020 09:42:03 +0800
From:   Wei Yang <richard.weiyang@...ux.alibaba.com>
To:     Mike Kravetz <mike.kravetz@...cle.com>
Cc:     Wei Yang <richard.weiyang@...ux.alibaba.com>,
        akpm@...ux-foundation.org, 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 Mon, Aug 31, 2020 at 04:06:54PM -0700, Mike Kravetz wrote:
>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.

Shame on me. You are right. I should change it to continue.

Andrew,

Sorry for the inconvenience.

>-- 
>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,
>> 

-- 
Wei Yang
Help you, Help me