linux-kernel - Re: [RFC PATCH 2/4] hugetlb: add support for preferred node to alloc_huge_page

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Date:   Wed, 14 Jun 2017 18:57:55 +0200
From:   Vlastimil Babka <vbabka@...e.cz>
To:     Michal Hocko <mhocko@...nel.org>
Cc:     linux-mm@...ck.org, Naoya Horiguchi <n-horiguchi@...jp.nec.com>,
        Mike Kravetz <mike.kravetz@...cle.com>,
        Mel Gorman <mgorman@...e.de>,
        Andrew Morton <akpm@...ux-foundation.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [RFC PATCH 2/4] hugetlb: add support for preferred node to
 alloc_huge_page_nodemask

On 06/14/2017 06:41 PM, Michal Hocko wrote:
> 
> This on top?
> ---
> diff --git a/mm/hugetlb.c b/mm/hugetlb.c
> index 9ac0ae725c5e..f9868e095afa 100644
> --- a/mm/hugetlb.c
> +++ b/mm/hugetlb.c
> @@ -902,7 +902,6 @@ static struct page *dequeue_huge_page_nodemask(struct hstate *h, gfp_t gfp_mask,
>  {
>  	unsigned int cpuset_mems_cookie;
>  	struct zonelist *zonelist;
> -	struct page *page = NULL;
>  	struct zone *zone;
>  	struct zoneref *z;
>  	int node = -1;
> @@ -912,6 +911,8 @@ static struct page *dequeue_huge_page_nodemask(struct hstate *h, gfp_t gfp_mask,
>  retry_cpuset:
>  	cpuset_mems_cookie = read_mems_allowed_begin();
>  	for_each_zone_zonelist_nodemask(zone, z, zonelist, gfp_zone(gfp_mask), nmask) {
> +		struct page *page;
> +
>  		if (!cpuset_zone_allowed(zone, gfp_mask))
>  			continue;
>  		/*
> @@ -924,9 +925,9 @@ static struct page *dequeue_huge_page_nodemask(struct hstate *h, gfp_t gfp_mask,
>  
>  		page = dequeue_huge_page_node_exact(h, node);
>  		if (page)
> -			break;
> +			return page;
>  	}
> -	if (unlikely(!page && read_mems_allowed_retry(cpuset_mems_cookie)))
> +	if (unlikely(read_mems_allowed_retry(cpuset_mems_cookie)))
>  		goto retry_cpuset;
>  
>  	return NULL;

OK

> @@ -1655,18 +1656,18 @@ struct page *alloc_huge_page_nodemask(struct hstate *h, int preferred_nid,
>  		nodemask_t *nmask)
>  {
>  	gfp_t gfp_mask = htlb_alloc_mask(h);
> -	struct page *page = NULL;
>  
>  	spin_lock(&hugetlb_lock);
>  	if (h->free_huge_pages - h->resv_huge_pages > 0) {
> +		struct page *page;
> +
>  		page = dequeue_huge_page_nodemask(h, gfp_mask, preferred_nid, nmask);
> -		if (page)
> -			goto unlock;
> +		if (page) {
> +			spin_unlock(&hugetlb_lock);
> +			return page;
> +		}

I thought you would just continue after the if (this is not a for-loop
after all), but this works too.

>  	}
> -unlock:
>  	spin_unlock(&hugetlb_lock);
> -	if (page)
> -		return page;
>  
>  	/* No reservations, try to overcommit */
>  
>