linux-kernel - Re: [Patch v3 4/4] mm/mremap: use pmd_addr_end to simplify the calculate of extent

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Date:   Wed, 8 Jul 2020 11:27:00 +0300
From:   "Kirill A. Shutemov" <kirill@...temov.name>
To:     Wei Yang <richard.weiyang@...ux.alibaba.com>
Cc:     akpm@...ux-foundation.org, kirill.shutemov@...ux.intel.com,
        vbabka@...e.cz, yang.shi@...ux.alibaba.com, thomas_os@...pmail.org,
        anshuman.khandual@....com, sean.j.christopherson@...el.com,
        peterx@...hat.com, aneesh.kumar@...ux.ibm.com, willy@...radead.org,
        thellstrom@...are.com, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, digetx@...il.com
Subject: Re: [Patch v3 4/4] mm/mremap: use pmd_addr_end to simplify the
 calculate of extent

On Wed, Jul 08, 2020 at 09:24:53AM +0800, Wei Yang wrote:
> The purpose of this code is to calculate the smaller extent in old and
> new range. Let's leverage pmd_addr_end() to do the calculation.
> 
> Hope this would make the code easier to read.
> 
> Signed-off-by: Wei Yang <richard.weiyang@...ux.alibaba.com>
> ---
>  mm/mremap.c | 16 +++++++---------
>  1 file changed, 7 insertions(+), 9 deletions(-)
> 
> diff --git a/mm/mremap.c b/mm/mremap.c
> index f5f17d050617..76e7fdf567c3 100644
> --- a/mm/mremap.c
> +++ b/mm/mremap.c
> @@ -237,11 +237,12 @@ unsigned long move_page_tables(struct vm_area_struct *vma,
>  		unsigned long new_addr, unsigned long len,
>  		bool need_rmap_locks)
>  {
> -	unsigned long extent, next, old_end;
> +	unsigned long extent, old_next, new_next, old_end, new_end;
>  	struct mmu_notifier_range range;
>  	pmd_t *old_pmd, *new_pmd;
>  
>  	old_end = old_addr + len;
> +	new_end = new_addr + len;
>  	flush_cache_range(vma, old_addr, old_end);
>  
>  	mmu_notifier_range_init(&range, MMU_NOTIFY_UNMAP, 0, vma, vma->vm_mm,
> @@ -250,14 +251,11 @@ unsigned long move_page_tables(struct vm_area_struct *vma,
>  
>  	for (; old_addr < old_end; old_addr += extent, new_addr += extent) {
>  		cond_resched();
> -		next = (old_addr + PMD_SIZE) & PMD_MASK;
> -		/* even if next overflowed, extent below will be ok */
> -		extent = next - old_addr;
> -		if (extent > old_end - old_addr)
> -			extent = old_end - old_addr;
> -		next = (new_addr + PMD_SIZE) & PMD_MASK;
> -		if (extent > next - new_addr)
> -			extent = next - new_addr;
> +
> +		old_next = pmd_addr_end(old_addr, old_end);
> +		new_next = pmd_addr_end(new_addr, new_end);
> +		extent = min((old_next - old_addr), (new_next - new_addr));

Nit: redundant parentheses.

-- 
 Kirill A. Shutemov