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Subject: Re: [PATCH v2] mm/mmap.c: refine find_vma_prev with rb_last
To:     Wei Yang <richardw.yang@linux.intel.com>,
        akpm@linux-foundation.org, mhocko@suse.com,
        kirill.shutemov@linux.intel.com
Cc:     linux-mm@kvack.org, linux-kernel@vger.kernel.org
References: <20190809001928.4950-1-richardw.yang@linux.intel.com>
From:   Vlastimil Babka <vbabka@suse.cz>
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Message-ID: <d47ee469-8ff6-d212-9c4b-242079e281e8@suse.cz>
Date:   Fri, 9 Aug 2019 10:03:20 +0200
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On 8/9/19 2:19 AM, Wei Yang wrote:
> When addr is out of the range of the whole rb_tree, pprev will points to
> the right-most node. rb_tree facility already provides a helper
> function, rb_last, to do this task. We can leverage this instead of
> re-implement it.
> 
> This patch refines find_vma_prev with rb_last to make it a little nicer
> to read.
> 
> Signed-off-by: Wei Yang <richardw.yang@linux.intel.com>

Acked-by: Vlastimil Babka <vbabka@suse.cz>

Nit below:

> ---
> v2: leverage rb_last
> ---
>  mm/mmap.c | 9 +++------
>  1 file changed, 3 insertions(+), 6 deletions(-)
> 
> diff --git a/mm/mmap.c b/mm/mmap.c
> index 7e8c3e8ae75f..f7ed0afb994c 100644
> --- a/mm/mmap.c
> +++ b/mm/mmap.c
> @@ -2270,12 +2270,9 @@ find_vma_prev(struct mm_struct *mm, unsigned long addr,
>  	if (vma) {
>  		*pprev = vma->vm_prev;
>  	} else {
> -		struct rb_node *rb_node = mm->mm_rb.rb_node;
> -		*pprev = NULL;
> -		while (rb_node) {
> -			*pprev = rb_entry(rb_node, struct vm_area_struct, vm_rb);
> -			rb_node = rb_node->rb_right;
> -		}
> +		struct rb_node *rb_node = rb_last(&mm->mm_rb);
> +		*pprev = !rb_node ? NULL :
> +			 rb_entry(rb_node, struct vm_area_struct, vm_rb);

It's perhaps more common to write it like:
*pprev = rb_node ? rb_entry(rb_node, struct vm_area_struct, vm_rb) : NULL;

>  	}
>  	return vma;
>  }
>