linux-kernel - Re: [PATCH v3 4/6] mm: introduce arch_do_swap_page_nr() which allows restore metadata for nr pages

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Date: Mon, 6 May 2024 10:51:16 -0600
From: Khalid Aziz <khalid.aziz@...cle.com>
To: Barry Song <21cnbao@...il.com>, akpm@...ux-foundation.org,
        linux-mm@...ck.org
Cc: baolin.wang@...ux.alibaba.com, chrisl@...nel.org, david@...hat.com,
        hanchuanhua@...o.com, hannes@...xchg.org, hughd@...gle.com,
        kasong@...cent.com, linux-kernel@...r.kernel.org, ryan.roberts@....com,
        surenb@...gle.com, v-songbaohua@...o.com, willy@...radead.org,
        xiang@...nel.org, ying.huang@...el.com, yosryahmed@...gle.com,
        yuzhao@...gle.com, ziy@...dia.com,
        "David S. Miller" <davem@...emloft.net>,
        Andreas Larsson <andreas@...sler.com>
Subject: Re: [PATCH v3 4/6] mm: introduce arch_do_swap_page_nr() which allows
 restore metadata for nr pages

On 5/2/24 18:50, Barry Song wrote:
> From: Barry Song <v-songbaohua@...o.com>
> 
> Should do_swap_page() have the capability to directly map a large folio,
> metadata restoration becomes necessary for a specified number of pages
> denoted as nr. It's important to highlight that metadata restoration is
> solely required by the SPARC platform, which, however, does not enable
> THP_SWAP. Consequently, in the present kernel configuration, there
> exists no practical scenario where users necessitate the restoration of
> nr metadata. Platforms implementing THP_SWAP might invoke this function
> with nr values exceeding 1, subsequent to do_swap_page() successfully
> mapping an entire large folio. Nonetheless, their arch_do_swap_page_nr()
> functions remain empty.
> 
> Cc: Khalid Aziz <khalid.aziz@...cle.com>
> Cc: "David S. Miller" <davem@...emloft.net>
> Cc: Andreas Larsson <andreas@...sler.com>
> Signed-off-by: Barry Song <v-songbaohua@...o.com>

Looks good to me.

Reviewed-by: Khalid Aziz <khalid.aziz@...cle.com>


> ---
>   include/linux/pgtable.h | 26 ++++++++++++++++++++------
>   mm/memory.c             |  3 ++-
>   2 files changed, 22 insertions(+), 7 deletions(-)
> 
> diff --git a/include/linux/pgtable.h b/include/linux/pgtable.h
> index 18019f037bae..463e84c3de26 100644
> --- a/include/linux/pgtable.h
> +++ b/include/linux/pgtable.h
> @@ -1084,6 +1084,15 @@ static inline int pgd_same(pgd_t pgd_a, pgd_t pgd_b)
>   })
>   
>   #ifndef __HAVE_ARCH_DO_SWAP_PAGE
> +static inline void arch_do_swap_page_nr(struct mm_struct *mm,
> +				     struct vm_area_struct *vma,
> +				     unsigned long addr,
> +				     pte_t pte, pte_t oldpte,
> +				     int nr)
> +{
> +
> +}
> +#else
>   /*
>    * Some architectures support metadata associated with a page. When a
>    * page is being swapped out, this metadata must be saved so it can be
> @@ -1092,12 +1101,17 @@ static inline int pgd_same(pgd_t pgd_a, pgd_t pgd_b)
>    * page as metadata for the page. arch_do_swap_page() can restore this
>    * metadata when a page is swapped back in.
>    */
> -static inline void arch_do_swap_page(struct mm_struct *mm,
> -				     struct vm_area_struct *vma,
> -				     unsigned long addr,
> -				     pte_t pte, pte_t oldpte)
> -{
> -
> +static inline void arch_do_swap_page_nr(struct mm_struct *mm,
> +					struct vm_area_struct *vma,
> +					unsigned long addr,
> +					pte_t pte, pte_t oldpte,
> +					int nr)
> +{
> +	for (int i = 0; i < nr; i++) {
> +		arch_do_swap_page(vma->vm_mm, vma, addr + i * PAGE_SIZE,
> +				pte_advance_pfn(pte, i),
> +				pte_advance_pfn(oldpte, i));
> +	}
>   }
>   #endif
>   
> diff --git a/mm/memory.c b/mm/memory.c
> index f033eb3528ba..74cdefd58f5f 100644
> --- a/mm/memory.c
> +++ b/mm/memory.c
> @@ -4266,7 +4266,8 @@ vm_fault_t do_swap_page(struct vm_fault *vmf)
>   	VM_BUG_ON(!folio_test_anon(folio) ||
>   			(pte_write(pte) && !PageAnonExclusive(page)));
>   	set_pte_at(vma->vm_mm, vmf->address, vmf->pte, pte);
> -	arch_do_swap_page(vma->vm_mm, vma, vmf->address, pte, vmf->orig_pte);
> +	arch_do_swap_page_nr(vma->vm_mm, vma, vmf->address,
> +			pte, vmf->orig_pte, 1);
>   
>   	folio_unlock(folio);
>   	if (folio != swapcache && swapcache) {