linux-kernel - Re: [PATCH v10 12/69] mm/mmap: use the maple tree for find_vma

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Message-ID: <8e4d37dc-722c-6b9d-b1fd-84df4a0076bb@redhat.com>
Date:   Tue, 21 Jun 2022 23:17:03 +0200
From:   David Hildenbrand <david@...hat.com>
To:     Liam Howlett <liam.howlett@...cle.com>,
        "maple-tree@...ts.infradead.org" <maple-tree@...ts.infradead.org>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        "damon @ lists . linux . dev" <damon@...ts.linux.dev>,
        SeongJae Park <sj@...nel.org>
Subject: Re: [PATCH v10 12/69] mm/mmap: use the maple tree for find_vma_prev()
 instead of the rbtree

On 21.06.22 22:46, Liam Howlett wrote:
> From: "Liam R. Howlett" <Liam.Howlett@...cle.com>
> 
> Use the maple tree's advanced API and a maple state to walk the tree for
> the entry at the address of the next vma, then use the maple state to walk
> back one entry to find the previous entry.
> 
> Add kernel documentation comments for this API.
> 
> Link: https://lkml.kernel.org/r/20220504010716.661115-14-Liam.Howlett@oracle.com
> Signed-off-by: Liam R. Howlett <Liam.Howlett@...cle.com>
> Signed-off-by: Matthew Wilcox (Oracle) <willy@...radead.org>
> Acked-by: Vlastimil Babka <vbabka@...e.cz>
> Cc: Catalin Marinas <catalin.marinas@....com>
> Cc: David Howells <dhowells@...hat.com>
> Cc: SeongJae Park <sj@...nel.org>
> Cc: Will Deacon <will@...nel.org>
> Cc: Davidlohr Bueso <dave@...olabs.net>
> Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
> ---
>  mm/mmap.c | 27 +++++++++++++++++----------
>  1 file changed, 17 insertions(+), 10 deletions(-)
> 
> diff --git a/mm/mmap.c b/mm/mmap.c
> index fdb61252448f..08845a0317bf 100644
> --- a/mm/mmap.c
> +++ b/mm/mmap.c
> @@ -2512,23 +2512,30 @@ struct vm_area_struct *find_vma(struct mm_struct *mm, unsigned long addr)
>  }
>  EXPORT_SYMBOL(find_vma);
>  
> -/*
> - * Same as find_vma, but also return a pointer to the previous VMA in *pprev.
> +/**
> + * find_vma_prev() - Find the VMA for a given address, or the next vma and
> + * set %pprev to the previous VMA, if any.
> + * @mm: The mm_struct to check
> + * @addr: The address
> + * @pprev: The pointer to set to the previous VMA
> + *
> + * Note that RCU lock is missing here since the external mmap_lock() is used
> + * instead.

Can we assert that, please?

> + *
> + * Returns: The VMA associated with @addr, or the next vma.
> + * May return %NULL in the case of no vma at addr or above.

Nit: Inconsistent use of VMA vs. vma.

>   */
>  struct vm_area_struct *
>  find_vma_prev(struct mm_struct *mm, unsigned long addr,
>  			struct vm_area_struct **pprev)
>  {
>  	struct vm_area_struct *vma;
> +	MA_STATE(mas, &mm->mm_mt, addr, addr);
>  
> -	vma = find_vma(mm, addr);
> -	if (vma) {
> -		*pprev = vma->vm_prev;
> -	} else {
> -		struct rb_node *rb_node = rb_last(&mm->mm_rb);
> -
> -		*pprev = rb_node ? rb_entry(rb_node, struct vm_area_struct, vm_rb) : NULL;
> -	}
> +	vma = mas_walk(&mas);
> +	*pprev = mas_prev(&mas, 0);
> +	if (!vma)
> +		vma = mas_next(&mas, ULONG_MAX);
>  	return vma;
>  }
>  
Reviewed-by: David Hildenbrand <david@...hat.com>

-- 
Thanks,

David / dhildenb