linux-kernel - Re: [PATCH mm-new 2/3] mm: clean up and expose is_guard_pte

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Message-ID: <e2c6f52b-23c3-40ef-99d3-325a0a3cb4d4@arm.com>
Date: Sun, 14 Sep 2025 22:08:22 +0530
From: Dev Jain <dev.jain@....com>
To: Lance Yang <lance.yang@...ux.dev>, akpm@...ux-foundation.org,
 david@...hat.com, lorenzo.stoakes@...cle.com
Cc: ziy@...dia.com, baolin.wang@...ux.alibaba.com, Liam.Howlett@...cle.com,
 npache@...hat.com, ryan.roberts@....com, baohua@...nel.org,
 ioworker0@...il.com, linux-kernel@...r.kernel.org, linux-mm@...ck.org,
 Kairui Song <kasong@...cent.com>
Subject: Re: [PATCH mm-new 2/3] mm: clean up and expose is_guard_pte_marker()


On 14/09/25 8:05 pm, Lance Yang wrote:
> From: Lance Yang <lance.yang@...ux.dev>
>
> is_guard_pte_marker() performs a redundant check because it calls both
> is_pte_marker() and is_guard_swp_entry(), both of which internally check
> for a PTE marker.
>
> is_guard_pte_marker()
>   |- is_pte_marker()
>   |   `- is_pte_marker_entry()  // First check
>   `- is_guard_swp_entry()
>       `- is_pte_marker_entry()  // Second, redundant check
>
> While a modern compiler could likely optimize this away, let's have clean
> code and not rely on it ;)
>
> Also, make it available for hugepage collapsing code.

The movement of the code should be merged with the next patch.

>
> Cc: Kairui Song <kasong@...cent.com>
> Signed-off-by: Lance Yang <lance.yang@...ux.dev>
> ---
>   include/linux/swapops.h | 6 ++++++
>   mm/madvise.c            | 6 ------
>   2 files changed, 6 insertions(+), 6 deletions(-)
>
> diff --git a/include/linux/swapops.h b/include/linux/swapops.h
> index 59c5889a4d54..7f5684fa043b 100644
> --- a/include/linux/swapops.h
> +++ b/include/linux/swapops.h
> @@ -469,6 +469,12 @@ static inline int is_guard_swp_entry(swp_entry_t entry)
>   		(pte_marker_get(entry) & PTE_MARKER_GUARD);
>   }
>   
> +static inline bool is_guard_pte_marker(pte_t ptent)
> +{
> +	return is_swap_pte(ptent) &&
> +	       is_guard_swp_entry(pte_to_swp_entry(ptent));
> +}
> +
>   /*
>    * This is a special version to check pte_none() just to cover the case when
>    * the pte is a pte marker.  It existed because in many cases the pte marker
> diff --git a/mm/madvise.c b/mm/madvise.c
> index 35ed4ab0d7c5..bd46e6788fac 100644
> --- a/mm/madvise.c
> +++ b/mm/madvise.c
> @@ -1069,12 +1069,6 @@ static bool is_valid_guard_vma(struct vm_area_struct *vma, bool allow_locked)
>   	return !(vma->vm_flags & disallowed);
>   }
>   
> -static bool is_guard_pte_marker(pte_t ptent)
> -{
> -	return is_pte_marker(ptent) &&
> -		is_guard_swp_entry(pte_to_swp_entry(ptent));
> -}
> -
>   static int guard_install_pud_entry(pud_t *pud, unsigned long addr,
>   				   unsigned long next, struct mm_walk *walk)
>   {