linux-kernel - Re: [PATCH] mm/hugetlb: remove redundant reservation check condition in alloc_huge

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Message-ID: <32f628d5-fa0c-2a81-2de4-d0a76d1c3e45@oracle.com>
Date:   Fri, 12 Feb 2021 17:15:53 -0800
From:   Mike Kravetz <mike.kravetz@...cle.com>
To:     Miaohe Lin <linmiaohe@...wei.com>, akpm@...ux-foundation.org
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm/hugetlb: remove redundant reservation check condition
 in alloc_huge_page()

On 2/9/21 11:54 PM, Miaohe Lin wrote:
> If there is no reservation corresponding to a vma, map_chg is always != 0,
> i.e. we can not meet the condition where a vma does not have reservation
> while map_chg = 0.

This commit message might be easier to understand?

vma_resv_map(vma) checks if a reserve map is associated with the vma.  The
routine vma_needs_reservation() will check vma_resv_map(vma) and return 1
if no reserv map is present.  map_chg is set to the return value of
vma_needs_reservation().  Therefore, !vma_resv_map(vma) is redundant in the
expression:
	map_chg || avoid_reserve || !vma_resv_map(vma);
Remove the redundant check.

-- 
Mike Kravetz

> 
> Signed-off-by: Miaohe Lin <linmiaohe@...wei.com>
> ---
>  mm/hugetlb.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/mm/hugetlb.c b/mm/hugetlb.c
> index 4f2c92ddbca4..36c3646fa55f 100644
> --- a/mm/hugetlb.c
> +++ b/mm/hugetlb.c
> @@ -2311,7 +2311,7 @@ struct page *alloc_huge_page(struct vm_area_struct *vma,
>  
>  	/* If this allocation is not consuming a reservation, charge it now.
>  	 */
> -	deferred_reserve = map_chg || avoid_reserve || !vma_resv_map(vma);
> +	deferred_reserve = map_chg || avoid_reserve;
>  	if (deferred_reserve) {
>  		ret = hugetlb_cgroup_charge_cgroup_rsvd(
>  			idx, pages_per_huge_page(h), &h_cg);
>