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Date: Sun, 4 Feb 2024 11:58:53 +0100
From: Mike Rapoport <rppt@kernel.org>
To: Qi Zheng <zhengqi.arch@bytedance.com>
Cc: akpm@linux-foundation.org, arnd@arndb.de, muchun.song@linux.dev,
	david@redhat.com, willy@infradead.org, linux-mm@kvack.org,
	linux-kernel@vger.kernel.org, linux-arch@vger.kernel.org
Subject: Re: [PATCH 1/2] mm: pgtable: add missing flag and statistics for
 kernel PTE page
Message-ID: <Zb9t7WtFbZofN5WZ@kernel.org>
References: <f023a6687b9f2109401e7522b727aa4708dc05f1.1706774109.git.zhengqi.arch@bytedance.com>
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In-Reply-To: <f023a6687b9f2109401e7522b727aa4708dc05f1.1706774109.git.zhengqi.arch@bytedance.com>

On Thu, Feb 01, 2024 at 04:05:40PM +0800, Qi Zheng wrote:
> For kernel PTE page, we do not need to allocate and initialize its split
> ptlock, but as a page table page, it's still necessary to add PG_table
> flag and NR_PAGETABLE statistics for it.
> 
> Signed-off-by: Qi Zheng <zhengqi.arch@bytedance.com>
> ---
>  include/asm-generic/pgalloc.h |  7 ++++++-
>  include/linux/mm.h            | 21 ++++++++++++++++-----
>  2 files changed, 22 insertions(+), 6 deletions(-)

This should also update the architectures that define
__HAVE_ARCH_PTE_ALLOC_ONE_KERNEL, otherwise NR_PAGETABLE counts will get
wrong.

Another related thing is that many architectures have custom allocations
for early page tables and these would also benefit form NR_PAGETABLE
accounting.
 
> diff --git a/include/asm-generic/pgalloc.h b/include/asm-generic/pgalloc.h
> index 879e5f8aa5e9..908bd9140ac2 100644
> --- a/include/asm-generic/pgalloc.h
> +++ b/include/asm-generic/pgalloc.h
> @@ -23,6 +23,8 @@ static inline pte_t *__pte_alloc_one_kernel(struct mm_struct *mm)
>  
>  	if (!ptdesc)
>  		return NULL;
> +
> +	__pagetable_pte_ctor(ptdesc);
>  	return ptdesc_address(ptdesc);
>  }
>  
> @@ -46,7 +48,10 @@ static inline pte_t *pte_alloc_one_kernel(struct mm_struct *mm)
>   */
>  static inline void pte_free_kernel(struct mm_struct *mm, pte_t *pte)
>  {
> -	pagetable_free(virt_to_ptdesc(pte));
> +	struct ptdesc *ptdesc = virt_to_ptdesc(pte);
> +
> +	__pagetable_pte_dtor(ptdesc);
> +	pagetable_free(ptdesc);
>  }
>  
>  /**
> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index e442fd0efdd9..e37db032764e 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -2922,26 +2922,37 @@ static inline bool ptlock_init(struct ptdesc *ptdesc) { return true; }
>  static inline void ptlock_free(struct ptdesc *ptdesc) {}
>  #endif /* USE_SPLIT_PTE_PTLOCKS */
>  
> -static inline bool pagetable_pte_ctor(struct ptdesc *ptdesc)
> +static inline void __pagetable_pte_ctor(struct ptdesc *ptdesc)
>  {
>  	struct folio *folio = ptdesc_folio(ptdesc);
>  
> -	if (!ptlock_init(ptdesc))
> -		return false;
>  	__folio_set_pgtable(folio);
>  	lruvec_stat_add_folio(folio, NR_PAGETABLE);
> +}
> +
> +static inline bool pagetable_pte_ctor(struct ptdesc *ptdesc)
> +{
> +	if (!ptlock_init(ptdesc))
> +		return false;
> +
> +	__pagetable_pte_ctor(ptdesc);
>  	return true;
>  }
>  
> -static inline void pagetable_pte_dtor(struct ptdesc *ptdesc)
> +static inline void __pagetable_pte_dtor(struct ptdesc *ptdesc)
>  {
>  	struct folio *folio = ptdesc_folio(ptdesc);
>  
> -	ptlock_free(ptdesc);
>  	__folio_clear_pgtable(folio);
>  	lruvec_stat_sub_folio(folio, NR_PAGETABLE);
>  }
>  
> +static inline void pagetable_pte_dtor(struct ptdesc *ptdesc)
> +{
> +	ptlock_free(ptdesc);
> +	__pagetable_pte_dtor(ptdesc);
> +}
> +
>  pte_t *__pte_offset_map(pmd_t *pmd, unsigned long addr, pmd_t *pmdvalp);
>  static inline pte_t *pte_offset_map(pmd_t *pmd, unsigned long addr)
>  {
> -- 
> 2.30.2
> 
> 

-- 
Sincerely yours,
Mike.