linux-kernel - Re: [PATCH 2/5] swap: avoid a redundant pte map if ra window is 1

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Date:   Fri, 09 Dec 2022 11:15:41 +0800
From:   "Huang, Ying" <ying.huang@...el.com>
To:     Kairui Song <ryncsn@...il.com>
Cc:     linux-mm@...ck.org, Kairui Song <kasong@...cent.com>,
        linux-kernel@...r.kernel.org,
        Andrew Morton <akpm@...ux-foundation.org>,
        Miaohe Lin <linmiaohe@...wei.com>,
        David Hildenbrand <david@...hat.com>,
        Hugh Dickins <hughd@...gle.com>
Subject: Re: [PATCH 2/5] swap: avoid a redundant pte map if ra window is 1

Kairui Song <ryncsn@...il.com> writes:

> From: Kairui Song <kasong@...cent.com>
>
> Avoid a redundant pte map/unmap when swap readahead window is 1.
>
> Signed-off-by: Kairui Song <kasong@...cent.com>
> ---
>  mm/swap_state.c | 7 ++-----
>  1 file changed, 2 insertions(+), 5 deletions(-)

Good to reduce the line of code.  Thanks!

Reviewed-by: "Huang, Ying" <ying.huang@...el.com>

> diff --git a/mm/swap_state.c b/mm/swap_state.c
> index 438d0676c5be..60136bda78e3 100644
> --- a/mm/swap_state.c
> +++ b/mm/swap_state.c
> @@ -730,8 +730,6 @@ static void swap_ra_info(struct vm_fault *vmf,
>  	}
>  
>  	faddr = vmf->address;
> -	orig_pte = pte = pte_offset_map(vmf->pmd, faddr);
> -
>  	fpfn = PFN_DOWN(faddr);
>  	ra_val = GET_SWAP_RA_VAL(vma);
>  	pfn = PFN_DOWN(SWAP_RA_ADDR(ra_val));
> @@ -742,12 +740,11 @@ static void swap_ra_info(struct vm_fault *vmf,
>  	atomic_long_set(&vma->swap_readahead_info,
>  			SWAP_RA_VAL(faddr, win, 0));
>  
> -	if (win == 1) {
> -		pte_unmap(orig_pte);
> +	if (win == 1)
>  		return;
> -	}
>  
>  	/* Copy the PTEs because the page table may be unmapped */
> +	orig_pte = pte = pte_offset_map(vmf->pmd, faddr);
>  	if (fpfn == pfn + 1)
>  		swap_ra_clamp_pfn(vma, faddr, fpfn, fpfn + win, &start, &end);
>  	else if (pfn == fpfn + 1)