Re: [PATCH] mm: Merge pte_mkhuge() call into arch_make_huge_pte()

[Christophe Leroy]

Le 02/02/2022 à 06:38, Anshuman Khandual a écrit :
> Each call into pte_mkhuge() is invariably followed by arch_make_huge_pte().
> Instead arch_make_huge_pte() can accommodate pte_mkhuge() at the beginning.
> This updates generic fallback stub for arch_make_huge_pte() and available
> platforms definitions. This makes huge pte creation much cleaner and easier
> to follow.

I think it is a good cleanup. I always wonder why commit d9ed9faac283 
("mm: add new arch_make_huge_pte() method for tile support") didn't move 
the pte_mkhuge() into arch_make_huge_pte().

When I implemented arch_make_huge_pte() for powerpc 8xx, in one case 
arch_make_huge_pte() have to undo the things done by pte_mkhuge(), see below

As a second step we could probably try to get rid of pte_mkhuge() 
completely, at least in the core.

> 
> Cc: Catalin Marinas <catalin.marinas@xxxxxxx>
> Cc: Will Deacon <will@xxxxxxxxxx>
> Cc: Michael Ellerman <mpe@xxxxxxxxxxxxxx>
> Cc: Paul Mackerras <paulus@xxxxxxxxx>
> Cc: "David S. Miller" <davem@xxxxxxxxxxxxx>
> Cc: Mike Kravetz <mike.kravetz@xxxxxxxxxx>
> Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> Cc: linux-arm-kernel@xxxxxxxxxxxxxxxxxxx
> Cc: linuxppc-dev@xxxxxxxxxxxxxxxx
> Cc: sparclinux@xxxxxxxxxxxxxxx
> Cc: linux-mm@xxxxxxxxx
> Cc: linux-kernel@xxxxxxxxxxxxxxx
> Signed-off-by: Anshuman Khandual <anshuman.khandual@xxxxxxx>

Reviewed-by: Christophe Leroy <christophe.leroy@xxxxxxxxxx>

> ---
>   arch/arm64/mm/hugetlbpage.c                      | 1 +
>   arch/powerpc/include/asm/nohash/32/hugetlb-8xx.h | 1 +
>   arch/sparc/mm/hugetlbpage.c                      | 1 +
>   include/linux/hugetlb.h                          | 2 +-
>   mm/hugetlb.c                                     | 3 +--
>   mm/vmalloc.c                                     | 1 -
>   6 files changed, 5 insertions(+), 4 deletions(-)
> 
> diff --git a/arch/arm64/mm/hugetlbpage.c b/arch/arm64/mm/hugetlbpage.c
> index ffb9c229610a..228226c5fa80 100644
> --- a/arch/arm64/mm/hugetlbpage.c
> +++ b/arch/arm64/mm/hugetlbpage.c
> @@ -347,6 +347,7 @@ pte_t arch_make_huge_pte(pte_t entry, unsigned int shift, vm_flags_t flags)
>   {
>   	size_t pagesize = 1UL << shift;
>   
> +	entry = pte_mkhuge(entry);
>   	if (pagesize == CONT_PTE_SIZE) {
>   		entry = pte_mkcont(entry);
>   	} else if (pagesize == CONT_PMD_SIZE) {
> diff --git a/arch/powerpc/include/asm/nohash/32/hugetlb-8xx.h b/arch/powerpc/include/asm/nohash/32/hugetlb-8xx.h
> index 64b6c608eca4..e41e095158c7 100644
> --- a/arch/powerpc/include/asm/nohash/32/hugetlb-8xx.h
> +++ b/arch/powerpc/include/asm/nohash/32/hugetlb-8xx.h
> @@ -70,6 +70,7 @@ static inline pte_t arch_make_huge_pte(pte_t entry, unsigned int shift, vm_flags
>   {
>   	size_t size = 1UL << shift;
>   
> +	entry = pte_mkhuge(entry);

Could drop that and replace the below by:

	if (size == SZ_16K)
		return __pte(pte_val(entry) | _PAGE_SPS);
	else
		return __pte(pte_val(entry) | _PAGE_SPS | _PAGE_HUGE);
	

>   	if (size == SZ_16K)
>   		return __pte(pte_val(entry) & ~_PAGE_HUGE);
>   	else
> diff --git a/arch/sparc/mm/hugetlbpage.c b/arch/sparc/mm/hugetlbpage.c
> index 0f49fada2093..d8e0e3c7038d 100644
> --- a/arch/sparc/mm/hugetlbpage.c
> +++ b/arch/sparc/mm/hugetlbpage.c
> @@ -181,6 +181,7 @@ pte_t arch_make_huge_pte(pte_t entry, unsigned int shift, vm_flags_t flags)
>   {
>   	pte_t pte;
>   
> +	entry = pte_mkhuge(entry);
>   	pte = hugepage_shift_to_tte(entry, shift);
>   
>   #ifdef CONFIG_SPARC64
> diff --git a/include/linux/hugetlb.h b/include/linux/hugetlb.h
> index d1897a69c540..52c462390aee 100644
> --- a/include/linux/hugetlb.h
> +++ b/include/linux/hugetlb.h
> @@ -754,7 +754,7 @@ static inline void arch_clear_hugepage_flags(struct page *page) { }
>   static inline pte_t arch_make_huge_pte(pte_t entry, unsigned int shift,
>   				       vm_flags_t flags)
>   {
> -	return entry;
> +	return pte_mkhuge(entry);
>   }
>   #endif
>   
> diff --git a/mm/hugetlb.c b/mm/hugetlb.c
> index 61895cc01d09..5ca253c1b4e4 100644
> --- a/mm/hugetlb.c
> +++ b/mm/hugetlb.c
> @@ -4637,7 +4637,6 @@ static pte_t make_huge_pte(struct vm_area_struct *vma, struct page *page,
>   					   vma->vm_page_prot));
>   	}
>   	entry = pte_mkyoung(entry);
> -	entry = pte_mkhuge(entry);
>   	entry = arch_make_huge_pte(entry, shift, vma->vm_flags);
>   
>   	return entry;
> @@ -6172,7 +6171,7 @@ unsigned long hugetlb_change_protection(struct vm_area_struct *vma,
>   			unsigned int shift = huge_page_shift(hstate_vma(vma));
>   
>   			old_pte = huge_ptep_modify_prot_start(vma, address, ptep);
> -			pte = pte_mkhuge(huge_pte_modify(old_pte, newprot));
> +			pte = huge_pte_modify(old_pte, newprot);
>   			pte = arch_make_huge_pte(pte, shift, vma->vm_flags);
>   			huge_ptep_modify_prot_commit(vma, address, ptep, old_pte, pte);
>   			pages++;
> diff --git a/mm/vmalloc.c b/mm/vmalloc.c
> index 4165304d3547..d0b14dd73adc 100644
> --- a/mm/vmalloc.c
> +++ b/mm/vmalloc.c
> @@ -118,7 +118,6 @@ static int vmap_pte_range(pmd_t *pmd, unsigned long addr, unsigned long end,
>   		if (size != PAGE_SIZE) {
>   			pte_t entry = pfn_pte(pfn, prot);
>   
> -			entry = pte_mkhuge(entry);
>   			entry = arch_make_huge_pte(entry, ilog2(size), 0);
>   			set_huge_pte_at(&init_mm, addr, pte, entry);
>   			pfn += PFN_DOWN(size);