linux-kernel - Re: [PATCH] arm64/mm: Drop redundant addr increment in set_huge_pte

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Message-ID: <408a830d-11c5-4c29-95c1-21789cd07e32@arm.com>
Date: Tue, 15 Jul 2025 12:06:34 +0530
From: Anshuman Khandual <anshuman.khandual@....com>
To: Dev Jain <dev.jain@....com>, linux-arm-kernel@...ts.infradead.org
Cc: Catalin Marinas <catalin.marinas@....com>, Will Deacon <will@...nel.org>,
 Ryan Roberts <ryan.roberts@....com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] arm64/mm: Drop redundant addr increment in
 set_huge_pte_at()



On 15/07/25 11:28 AM, Dev Jain wrote:
> 
> On 15/07/25 10:09 am, Anshuman Khandual wrote:
>> The 'addr' need not be incremented while operating on single entry basis as
>> BBM is not required for such updates.
> 
> "while operating on a single entry basis" should be replaced with
> "when transitioning from invalid to valid pte"; BBM is required
> for single entry updates when the cont bit is set, as described
> in the comment immediately below. In fact, let us not even mention
> BBM at all - the reasoning is that the code is written in a way
> that, the loop incrementing addr, immediately has a return after
> it, and it does not actually use the addr, so let's drop the
> increment. It is not immediately obvious from the commit description
> that the addr is passed ultimately to flush_tlb_range friends which
> is involved in BBM.

Agreed, the mention about BBM can be dropped as it is not really
relevant. Rather 'addr' variable being unused in the conditional
block, which exits right after is the real reason. I will update
the commit description as required.  

> 
> Reviewed-by: Dev Jain <dev.jain@....com>
> 
>>
>> Cc: Catalin Marinas <catalin.marinas@....com>
>> Cc: Will Deacon <will@...nel.org>
>> Cc: Ryan Roberts <ryan.roberts@....com>
>> Cc: linux-arm-kernel@...ts.infradead.org
>> Cc: linux-kernel@...r.kernel.org
>> Signed-off-by: Anshuman Khandual <anshuman.khandual@....com>
>> ---
>>   arch/arm64/mm/hugetlbpage.c | 2 +-
>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/arch/arm64/mm/hugetlbpage.c b/arch/arm64/mm/hugetlbpage.c
>> index 0c8737f4f2ce..1d90a7e75333 100644
>> --- a/arch/arm64/mm/hugetlbpage.c
>> +++ b/arch/arm64/mm/hugetlbpage.c
>> @@ -225,7 +225,7 @@ void set_huge_pte_at(struct mm_struct *mm, unsigned long addr,
>>       ncontig = num_contig_ptes(sz, &pgsize);
>>         if (!pte_present(pte)) {
>> -        for (i = 0; i < ncontig; i++, ptep++, addr += pgsize)
>> +        for (i = 0; i < ncontig; i++, ptep++)
>>               __set_ptes_anysz(mm, ptep, pte, 1, pgsize);
>>           return;
>>       }