linux-kernel - Re: [PATCH v2 3/7] mm: Add batched versions of ptep_modify_prot

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Message-ID: <f0c57d50-075e-4ff3-9bcd-4b223eb9fd8a@redhat.com>
Date: Tue, 6 May 2025 16:30:18 +0200
From: David Hildenbrand <david@...hat.com>
To: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>, Dev Jain <dev.jain@....com>
Cc: akpm@...ux-foundation.org, ryan.roberts@....com, willy@...radead.org,
 linux-mm@...ck.org, linux-kernel@...r.kernel.org, catalin.marinas@....com,
 will@...nel.org, Liam.Howlett@...cle.com, vbabka@...e.cz, jannh@...gle.com,
 anshuman.khandual@....com, peterx@...hat.com, joey.gouly@....com,
 ioworker0@...il.com, baohua@...nel.org, kevin.brodsky@....com,
 quic_zhenhuah@...cinc.com, christophe.leroy@...roup.eu,
 yangyicong@...ilicon.com, linux-arm-kernel@...ts.infradead.org,
 namit@...are.com, hughd@...gle.com, yang@...amperecomputing.com,
 ziy@...dia.com
Subject: Re: [PATCH v2 3/7] mm: Add batched versions of
 ptep_modify_prot_start/commit

On 30.04.25 16:37, Lorenzo Stoakes wrote:
> On Wed, Apr 30, 2025 at 11:55:12AM +0530, Dev Jain wrote:
>>
>>
>> On 29/04/25 7:22 pm, Lorenzo Stoakes wrote:
>>> On Tue, Apr 29, 2025 at 10:53:32AM +0530, Dev Jain wrote:
>>>> Batch ptep_modify_prot_start/commit in preparation for optimizing mprotect.
>>>> Architecture can override these helpers.
>>>>
>>>> Signed-off-by: Dev Jain <dev.jain@....com>
>>>> ---
>>>>    include/linux/pgtable.h | 38 ++++++++++++++++++++++++++++++++++++++
>>>>    1 file changed, 38 insertions(+)
>>>>
>>>> diff --git a/include/linux/pgtable.h b/include/linux/pgtable.h
>>>> index b50447ef1c92..ed287289335f 100644
>>>> --- a/include/linux/pgtable.h
>>>> +++ b/include/linux/pgtable.h
>>>> @@ -891,6 +891,44 @@ static inline void wrprotect_ptes(struct mm_struct *mm, unsigned long addr,
>>>>    }
>>>>    #endif
>>>>
>>>> +/* See the comment for ptep_modify_prot_start */
>>>
>>> I feel like you really should add a little more here, perhaps point out
>>> that it's batched etc.
>>
>> Sure. I couldn't easily figure out a way to write the documentation nicely,
>> I'll do it this time.
> 
> Thanks! Though see the discussion with Ryan also.
> 
>>
>>>
>>>> +#ifndef modify_prot_start_ptes
>>>> +static inline pte_t modify_prot_start_ptes(struct vm_area_struct *vma,
>>>> +		unsigned long addr, pte_t *ptep, unsigned int nr)
>>>
>>> This name is a bit confusing, it's not any ptes, it's those pte entries
>>> belonging to a large folio capped to the PTE table right that you are
>>> batching right?
>>
>> yes, but I am just following the convention. See wrprotect_ptes(), etc. I
>> don't have a strong preference anyways.
>>
>>>
>>> Perhaps modify_prot_start_large_folio() ? Or something with 'batched' in
>>> the name?
>>
>> How about modify_prot_start_batched_ptes()?
> 
> I like this :) Ryan - that work for you, or do you feel _batched_ should be
> dropped here?


modify_prot_start_folio_ptes ?

But I would rather go with

modify_prot_folio_ptes_start

The "batched" is implicit, and "large folio" is not required if it's 
more than one pte ...

:)

-- 
Cheers,

David / dhildenb