From: Lance Yang <lance.yang@linux.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.

Cc: Kairui Song <kasong@tencent.com>
Signed-off-by: Lance Yang <lance.yang@linux.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)
 {
-- 
2.49.0

On 14.09.25 16:35, Lance Yang wrote:
> From: Lance Yang <lance.yang@linux.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.
> 
> Cc: Kairui Song <kasong@tencent.com>
> Signed-off-by: Lance Yang <lance.yang@linux.dev>
> ---

Acked-by: David Hildenbrand <david@redhat.com>

-- 
Cheers

David / dhildenb

On Sun, Sep 14, 2025 at 10:35:46PM +0800, Lance Yang wrote:
> From: Lance Yang <lance.yang@linux.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
>

I mean, it expands to:

is_swap_pte(pte) && is_pte_marker_entry(pte_to_swp_entry(pte)) &&
is_pte_marker_entry(pte_to_swp_entry(pte))

So I don't think it's really unreasonable to expect compiler magic here...

But you're right that I should have just used is_swap_pte() really, it's a bit
silly not to, so this is fine :)

> While a modern compiler could likely optimize this away, let's have clean
> code and not rely on it ;)

Please don't put smileys in commit messages :) as cute as they are, this is
going on the permanent kernel record and while we all love them, it's
probably not the best place to put them :P

>
> Also, make it available for hugepage collapsing code.

Nit but put a newline after this.

I think probably if I'm really really nitty I'd say that you should put
this bit first, as it's the primary motivation for the change, and put the
refactoring stuff after.

> Cc: Kairui Song <kasong@tencent.com>
> Signed-off-by: Lance Yang <lance.yang@linux.dev>

This seems fine to me, so:

Reviewed-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>

> ---
>  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)
>  {
> --
> 2.49.0
>

Hi Lorenzo,

Thanks for taking time to review!

On 2025/9/15 21:54, Lorenzo Stoakes wrote:
> On Sun, Sep 14, 2025 at 10:35:46PM +0800, Lance Yang wrote:
>> From: Lance Yang <lance.yang@linux.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
>>
> 
> I mean, it expands to:
> 
> is_swap_pte(pte) && is_pte_marker_entry(pte_to_swp_entry(pte)) &&
> is_pte_marker_entry(pte_to_swp_entry(pte))

Yes, that's a much clearer way to lay it out ;)

> 
> So I don't think it's really unreasonable to expect compiler magic here...
> 
> But you're right that I should have just used is_swap_pte() really, it's a bit
> silly not to, so this is fine :)

Exactly. Glad we're on the same page!

> 
>> While a modern compiler could likely optimize this away, let's have clean
>> code and not rely on it ;)
> 
> Please don't put smileys in commit messages :) as cute as they are, this is
> going on the permanent kernel record and while we all love them, it's
> probably not the best place to put them :P
> 
>>
>> Also, make it available for hugepage collapsing code.
> 
> Nit but put a newline after this.

Got it. Will fix up all nits in v2.

> 
> I think probably if I'm really really nitty I'd say that you should put
> this bit first, as it's the primary motivation for the change, and put the
> refactoring stuff after.

Ah, right. The motivation for exposing the helper should come first. I'll
reorder this changelog in v2.

> 
>> Cc: Kairui Song <kasong@tencent.com>
>> Signed-off-by: Lance Yang <lance.yang@linux.dev>
> 
> This seems fine to me, so:
> 
> Reviewed-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>

Thanks,
Lance

> 
>> ---
>>   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)
>>   {
>> --
>> 2.49.0
>>

On 14/09/25 8:05 pm, Lance Yang wrote:
> From: Lance Yang <lance.yang@linux.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@tencent.com>
> Signed-off-by: Lance Yang <lance.yang@linux.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)
>   {

On 2025/9/15 00:38, Dev Jain wrote:
> 
> On 14/09/25 8:05 pm, Lance Yang wrote:
>> From: Lance Yang <lance.yang@linux.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.

Thanks for the suggestion ;)

I'd prefer to keep them as separate patches to make them easier to review,
if that's okay.

Cheers,
Lance

> 
>>
>> Cc: Kairui Song <kasong@tencent.com>
>> Signed-off-by: Lance Yang <lance.yang@linux.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)
>>   {