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Date: Mon, 3 Jun 2024 11:03:55 +0200
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Subject: Re: [PATCH 1/1] mm/mlock: implement folio_mlock_step() using
 folio_pte_batch()
To: Baolin Wang <baolin.wang@linux.alibaba.com>,
 Barry Song <21cnbao@gmail.com>, Lance Yang <ioworker0@gmail.com>
Cc: akpm@linux-foundation.org, ryan.roberts@arm.com, ziy@nvidia.com,
 fengwei.yin@intel.com, ying.huang@intel.com, libang.li@antgroup.com,
 linux-mm@kvack.org, linux-kernel@vger.kernel.org
References: <20240603033118.76457-1-ioworker0@gmail.com>
 <CAGsJ_4wxPk+bk9UM+PvA3x=LJG+mWmTD3e2HSEsS83X3vMWTJQ@mail.gmail.com>
 <c925eae9-5c7e-47d2-bab3-708edec88990@linux.alibaba.com>
From: David Hildenbrand <david@redhat.com>
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Organization: Red Hat
In-Reply-To: <c925eae9-5c7e-47d2-bab3-708edec88990@linux.alibaba.com>
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On 03.06.24 10:58, Baolin Wang wrote:
> 
> 
> On 2024/6/3 12:14, Barry Song wrote:
>> On Mon, Jun 3, 2024 at 3:31 PM Lance Yang <ioworker0@gmail.com> wrote:
>>>
>>> Let's make folio_mlock_step() simply a wrapper around folio_pte_batch(),
>>> which will greatly reduce the cost of ptep_get() when scanning a range of
>>> contptes.
>>>
>>> Signed-off-by: Lance Yang <ioworker0@gmail.com>
>>> ---
>>>    mm/mlock.c | 23 ++++++-----------------
>>>    1 file changed, 6 insertions(+), 17 deletions(-)
>>>
>>> diff --git a/mm/mlock.c b/mm/mlock.c
>>> index 30b51cdea89d..1ae6232d38cf 100644
>>> --- a/mm/mlock.c
>>> +++ b/mm/mlock.c
>>> @@ -307,26 +307,15 @@ void munlock_folio(struct folio *folio)
>>>    static inline unsigned int folio_mlock_step(struct folio *folio,
>>>                   pte_t *pte, unsigned long addr, unsigned long end)
>>>    {
>>> -       unsigned int count, i, nr = folio_nr_pages(folio);
>>> -       unsigned long pfn = folio_pfn(folio);
>>> -       pte_t ptent = ptep_get(pte);
>>> -
>>> -       if (!folio_test_large(folio))
>>> +       if (likely(!folio_test_large(folio)))
>>>                   return 1;
>>>
>>> -       count = pfn + nr - pte_pfn(ptent);
>>> -       count = min_t(unsigned int, count, (end - addr) >> PAGE_SHIFT);
>>> -
>>> -       for (i = 0; i < count; i++, pte++) {
>>> -               pte_t entry = ptep_get(pte);
>>> -
>>> -               if (!pte_present(entry))
>>> -                       break;
>>> -               if (pte_pfn(entry) - pfn >= nr)
>>> -                       break;
>>> -       }
>>> +       const fpb_t fpb_flags = FPB_IGNORE_DIRTY | FPB_IGNORE_SOFT_DIRTY;
>>> +       int max_nr = (end - addr) / PAGE_SIZE;
>>> +       pte_t ptent = ptep_get(pte);
>>>
>>> -       return i;
>>> +       return folio_pte_batch(folio, addr, pte, ptent, max_nr, fpb_flags, NULL,
>>> +                              NULL, NULL);
>>>    }
>>
>> what about a minimum change as below?
>> index 30b51cdea89d..e8b98f84fbd2 100644
>> --- a/mm/mlock.c
>> +++ b/mm/mlock.c
>> @@ -307,26 +307,15 @@ void munlock_folio(struct folio *folio)
>>    static inline unsigned int folio_mlock_step(struct folio *folio,
>>                   pte_t *pte, unsigned long addr, unsigned long end)
>>    {
>> -       unsigned int count, i, nr = folio_nr_pages(folio);
>> -       unsigned long pfn = folio_pfn(folio);
>> +       unsigned int count = (end - addr) >> PAGE_SHIFT;
>>           pte_t ptent = ptep_get(pte);
>> +       const fpb_t fpb_flags = FPB_IGNORE_DIRTY | FPB_IGNORE_SOFT_DIRTY;
>>
>>           if (!folio_test_large(folio))
>>                   return 1;
>>
>> -       count = pfn + nr - pte_pfn(ptent);
>> -       count = min_t(unsigned int, count, (end - addr) >> PAGE_SHIFT);
>> -
>> -       for (i = 0; i < count; i++, pte++) {
>> -               pte_t entry = ptep_get(pte);
>> -
>> -               if (!pte_present(entry))
>> -                       break;
>> -               if (pte_pfn(entry) - pfn >= nr)
>> -                       break;
>> -       }
>> -
>> -       return i;
>> +       return folio_pte_batch(folio, addr, pte, ptent, count, fpb_flags, NULL,
>> +                              NULL, NULL);
>>    }
> 
> LGTM.
> Reviewed-by: Baolin Wang <baolin.wang@linux.alibaba.com>
> 

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

-- 
Cheers,

David / dhildenb