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

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Message-Id: <20220618115909.5f2d1a4da68cc4115e73d14a@linux-foundation.org>
Date:   Sat, 18 Jun 2022 11:59:09 -0700
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     Miaohe Lin <linmiaohe@...wei.com>
Cc:     <linux-mm@...ck.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] mm/madvise: minor cleanup for swapin_walk_pmd_entry()

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'

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;
_