linux-kernel - Re: [PATCH 1/1] mm/mlock: implement folio_mlock_step() using folio_pte

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Date: Mon, 3 Jun 2024 16:58:58 +0800
From: Baolin Wang <baolin.wang@...ux.alibaba.com>
To: Barry Song <21cnbao@...il.com>, Lance Yang <ioworker0@...il.com>
Cc: akpm@...ux-foundation.org, ryan.roberts@....com, david@...hat.com,
 ziy@...dia.com, fengwei.yin@...el.com, ying.huang@...el.com,
 libang.li@...group.com, linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/1] mm/mlock: implement folio_mlock_step() using
 folio_pte_batch()



On 2024/6/3 12:14, Barry Song wrote:
> On Mon, Jun 3, 2024 at 3:31 PM Lance Yang <ioworker0@...il.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@...il.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@...ux.alibaba.com>