linux-kernel - Re: [PATCH] mm/madvise: minor cleanup for swapin_walk_pmd

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Date:   Mon, 20 Jun 2022 09:37:46 +0800
From:   Miaohe Lin <linmiaohe@...wei.com>
To:     Andrew Morton <akpm@...ux-foundation.org>
CC:     <linux-mm@...ck.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] mm/madvise: minor cleanup for swapin_walk_pmd_entry()

On 2022/6/19 2:59, Andrew Morton wrote:
> On Sat, 18 Jun 2022 17:05:27 +0800 Miaohe Lin <linmiaohe@...wei.com> wrote:
> 
>> Passing index to pte_offset_map_lock() directly so the below calculation
>> can be avoided. Rename orig_pte to ptep as it's not changed. Also use
>> helper is_swap_pte() to improve the readability. No functional change
>> intended.
>>
>> ...
>>
>> --- a/mm/madvise.c
>> +++ b/mm/madvise.c
>> @@ -195,7 +195,7 @@ static int madvise_update_vma(struct vm_area_struct *vma,
>>  static int swapin_walk_pmd_entry(pmd_t *pmd, unsigned long start,
>>  	unsigned long end, struct mm_walk *walk)
>>  {
>> -	pte_t *orig_pte;
>> +	pte_t *ptep;
>>  	struct vm_area_struct *vma = walk->private;
>>  	unsigned long index;
>>  	struct swap_iocb *splug = NULL;
>> @@ -209,11 +209,11 @@ static int swapin_walk_pmd_entry(pmd_t *pmd, unsigned long start,
>>  		struct page *page;
>>  		spinlock_t *ptl;
>>  
>> -		orig_pte = pte_offset_map_lock(vma->vm_mm, pmd, start, &ptl);
>> -		pte = *(orig_pte + ((index - start) / PAGE_SIZE));
>> -		pte_unmap_unlock(orig_pte, ptl);
>> +		ptep = pte_offset_map_lock(vma->vm_mm, pmd, index, &ptl);
>> +		pte = *ptep;
>> +		pte_unmap_unlock(ptep, ptl);
>>  
>> -		if (pte_present(pte) || pte_none(pte))
>> +		if (!is_swap_pte(pte))
>>  			continue;
>>  		entry = pte_to_swp_entry(pte);
>>  		if (unlikely(non_swap_entry(entry)))
> 
> Also...
> 
> From: Andrew Morton <akpm@...ux-foundation.org>
> Subject: mm-madvise-minor-cleanup-for-swapin_walk_pmd_entry-fix
> Date: Sat Jun 18 11:58:03 AM PDT 2022
> 
> reduce scope of `ptep'

Looks good to me. Thanks for doing this. :)

> 
> Cc: Miaohe Lin <linmiaohe@...wei.com>
> Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
> ---
> 
>  mm/madvise.c |    2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> --- a/mm/madvise.c~mm-madvise-minor-cleanup-for-swapin_walk_pmd_entry-fix
> +++ a/mm/madvise.c
> @@ -195,7 +195,6 @@ success:
>  static int swapin_walk_pmd_entry(pmd_t *pmd, unsigned long start,
>  	unsigned long end, struct mm_walk *walk)
>  {
> -	pte_t *ptep;
>  	struct vm_area_struct *vma = walk->private;
>  	unsigned long index;
>  	struct swap_iocb *splug = NULL;
> @@ -208,6 +207,7 @@ static int swapin_walk_pmd_entry(pmd_t *
>  		swp_entry_t entry;
>  		struct page *page;
>  		spinlock_t *ptl;
> +		pte_t *ptep;
>  
>  		ptep = pte_offset_map_lock(vma->vm_mm, pmd, index, &ptl);
>  		pte = *ptep;
> _
> 
> .
>