linux-kernel - Re: [PATCH v2 12/20] mm, hugetlb: remove vma_has

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Date:	Thu, 22 Aug 2013 14:14:38 +0530
From:	"Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>
To:	Joonsoo Kim <iamjoonsoo.kim@....com>,
	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Rik van Riel <riel@...hat.com>, Mel Gorman <mgorman@...e.de>,
	Michal Hocko <mhocko@...e.cz>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Hugh Dickins <hughd@...gle.com>,
	Davidlohr Bueso <davidlohr.bueso@...com>,
	David Gibson <david@...son.dropbear.id.au>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org, Joonsoo Kim <js1304@...il.com>,
	Wanpeng Li <liwanp@...ux.vnet.ibm.com>,
	Naoya Horiguchi <n-horiguchi@...jp.nec.com>,
	Hillf Danton <dhillf@...il.com>,
	Joonsoo Kim <iamjoonsoo.kim@....com>
Subject: Re: [PATCH v2 12/20] mm, hugetlb: remove vma_has_reserves()

Joonsoo Kim <iamjoonsoo.kim@....com> writes:

> vma_has_reserves() can be substituted by using return value of
> vma_needs_reservation(). If chg returned by vma_needs_reservation()
> is 0, it means that vma has reserves. Otherwise, it means that vma don't
> have reserves and need a hugepage outside of reserve pool. This definition
> is perfectly same as vma_has_reserves(), so remove vma_has_reserves().
>
> Signed-off-by: Joonsoo Kim <iamjoonsoo.kim@....com>

Reviewed-by: Aneesh Kumar K.V <aneesh.kumar@...ux.vnet.ibm.com>

>
> diff --git a/mm/hugetlb.c b/mm/hugetlb.c
> index e6c0c77..22ceb04 100644
> --- a/mm/hugetlb.c
> +++ b/mm/hugetlb.c
> @@ -473,39 +473,6 @@ void reset_vma_resv_huge_pages(struct vm_area_struct *vma)
>  		vma->vm_private_data = (void *)0;
>  }
>
> -/* Returns true if the VMA has associated reserve pages */
> -static int vma_has_reserves(struct vm_area_struct *vma, long chg)
> -{
> -	if (vma->vm_flags & VM_NORESERVE) {
> -		/*
> -		 * This address is already reserved by other process(chg == 0),
> -		 * so, we should decreament reserved count. Without
> -		 * decreamenting, reserve count is remained after releasing
> -		 * inode, because this allocated page will go into page cache
> -		 * and is regarded as coming from reserved pool in releasing
> -		 * step. Currently, we don't have any other solution to deal
> -		 * with this situation properly, so add work-around here.
> -		 */
> -		if (vma->vm_flags & VM_MAYSHARE && chg == 0)
> -			return 1;
> -		else
> -			return 0;
> -	}
> -
> -	/* Shared mappings always use reserves */
> -	if (vma->vm_flags & VM_MAYSHARE)
> -		return 1;
> -
> -	/*
> -	 * Only the process that called mmap() has reserves for
> -	 * private mappings.
> -	 */
> -	if (is_vma_resv_set(vma, HPAGE_RESV_OWNER))
> -		return 1;
> -
> -	return 0;
> -}
> -
>  static void copy_gigantic_page(struct page *dst, struct page *src)
>  {
>  	int i;
> @@ -580,8 +547,7 @@ static struct page *dequeue_huge_page_vma(struct hstate *h,
>  	 * have no page reserves. This check ensures that reservations are
>  	 * not "stolen". The child may still get SIGKILLed
>  	 */
> -	if (!vma_has_reserves(vma, chg) &&
> -			h->free_huge_pages - h->resv_huge_pages == 0)
> +	if (chg && h->free_huge_pages - h->resv_huge_pages == 0)
>  		return NULL;
>
>  	/* If reserves cannot be used, ensure enough pages are in the pool */
> @@ -600,7 +566,7 @@ retry_cpuset:
>  			if (page) {
>  				if (avoid_reserve)
>  					break;
> -				if (!vma_has_reserves(vma, chg))
> +				if (chg)
>  					break;
>
>  				SetPagePrivate(page);

Can you add a comment above both the place to explain why checking chg
is good enough ?

-aneesh

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