linux-kernel - Re: [PATCH 04/16] mm/huge_memory: use helper touch_pud in huge_pud_set

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Message-ID: <YrQLY7WzgXPM/LqJ@FVFYT0MHHV2J.usts.net>
Date:   Thu, 23 Jun 2022 14:42:43 +0800
From:   Muchun Song <songmuchun@...edance.com>
To:     Miaohe Lin <linmiaohe@...wei.com>
Cc:     akpm@...ux-foundation.org, shy828301@...il.com,
        willy@...radead.org, zokeefe@...gle.com, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 04/16] mm/huge_memory: use helper touch_pud in
 huge_pud_set_accessed

On Thu, Jun 23, 2022 at 01:06:15AM +0800, Miaohe Lin wrote:
> Use helper touch_pud to set pud accessed to simplify the code and improve
> the readability. No functional change intended.
> 
> Signed-off-by: Miaohe Lin <linmiaohe@...wei.com>
> ---
>  mm/huge_memory.c | 14 ++++----------
>  1 file changed, 4 insertions(+), 10 deletions(-)
> 
> diff --git a/mm/huge_memory.c b/mm/huge_memory.c
> index a26580da8011..a0c0e4bf9c1e 100644
> --- a/mm/huge_memory.c
> +++ b/mm/huge_memory.c
> @@ -1281,21 +1281,15 @@ int copy_huge_pud(struct mm_struct *dst_mm, struct mm_struct *src_mm,
>  
>  void huge_pud_set_accessed(struct vm_fault *vmf, pud_t orig_pud)
>  {
> -	pud_t entry;
> -	unsigned long haddr;
> -	bool write = vmf->flags & FAULT_FLAG_WRITE;
> +	int flags = 0;
>  
>  	vmf->ptl = pud_lock(vmf->vma->vm_mm, vmf->pud);
>  	if (unlikely(!pud_same(*vmf->pud, orig_pud)))
>  		goto unlock;
>  
> -	entry = pud_mkyoung(orig_pud);
> -	if (write)
> -		entry = pud_mkdirty(entry);
> -	haddr = vmf->address & HPAGE_PUD_MASK;
> -	if (pudp_set_access_flags(vmf->vma, haddr, vmf->pud, entry, write))
> -		update_mmu_cache_pud(vmf->vma, vmf->address, vmf->pud);
> -
> +	if (vmf->flags & FAULT_FLAG_WRITE)
> +		flags = FOLL_WRITE;

FOLL_* flags are used for follow_page(). But huge_pud_set_accessed() is used in mm fault
path. It is a little weird to me to use FOLL_WRITE here. I suggest replace the last
parameter of touch_pud() to "bool writable", then passing "vmf->flags & FAULT_FLAG_WRITE"
to it instead of converting from FAULT_FLAG* flag to FOLL* flag.

Thanks.

> +	touch_pud(vmf->vma, vmf->address, vmf->pud, flags);
>  unlock:
>  	spin_unlock(vmf->ptl);
>  }
> -- 
> 2.23.0
> 
>