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

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Message-ID: <434ecc5a-3aec-4381-8477-8a7d09220051@linux.dev>
Date: Mon, 15 Sep 2025 12:24:19 +0800
From: Lance Yang <lance.yang@...ux.dev>
To: Dev Jain <dev.jain@....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, lorenzo.stoakes@...cle.com,
 linux-kernel@...r.kernel.org, linux-mm@...ck.org,
 Kairui Song <kasong@...cent.com>, akpm@...ux-foundation.org, david@...hat.com
Subject: Re: [PATCH mm-new 2/3] mm: clean up and expose is_guard_pte_marker()


On 2025/9/15 00:38, Dev Jain wrote:
> 
> 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.

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@...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)
>>   {