linux-kernel - Re: [PATCH v2 2/2] mm: remove odd HAVE_PTE

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Message-ID: <3f20ac8b-20b8-f052-bc44-dcc0316354ca@arm.com>
Date:   Tue, 10 Apr 2018 16:58:48 +0100
From:   Robin Murphy <robin.murphy@....com>
To:     Laurent Dufour <ldufour@...ux.vnet.ibm.com>,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        linuxppc-dev@...ts.ozlabs.org, x86@...nel.org,
        linux-doc@...r.kernel.org, linux-snps-arc@...ts.infradead.org,
        linux-arm-kernel@...ts.infradead.org,
        linux-riscv@...ts.infradead.org, linux-s390@...r.kernel.org,
        linux-sh@...r.kernel.org, sparclinux@...r.kernel.org,
        Jerome Glisse <jglisse@...hat.com>, mhocko@...nel.org,
        aneesh.kumar@...ux.vnet.ibm.com, akpm@...ux-foundation.org,
        mpe@...erman.id.au, benh@...nel.crashing.org, paulus@...ba.org,
        Jonathan Corbet <corbet@....net>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will.deacon@....com>,
        Yoshinori Sato <ysato@...rs.sourceforge.jp>,
        Rich Felker <dalias@...c.org>,
        "David S . Miller" <davem@...emloft.net>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        Vineet Gupta <vgupta@...opsys.com>,
        Palmer Dabbelt <palmer@...ive.com>,
        Albert Ou <albert@...ive.com>,
        Martin Schwidefsky <schwidefsky@...ibm.com>,
        Heiko Carstens <heiko.carstens@...ibm.com>,
        David Rientjes <rientjes@...gle.com>
Subject: Re: [PATCH v2 2/2] mm: remove odd HAVE_PTE_SPECIAL

On 10/04/18 16:25, Laurent Dufour wrote:
> Remove the additional define HAVE_PTE_SPECIAL and rely directly on
> CONFIG_ARCH_HAS_PTE_SPECIAL.
> 
> There is no functional change introduced by this patch
> 
> Signed-off-by: Laurent Dufour <ldufour@...ux.vnet.ibm.com>
> ---
>   mm/memory.c | 23 ++++++++++-------------
>   1 file changed, 10 insertions(+), 13 deletions(-)
> 
> diff --git a/mm/memory.c b/mm/memory.c
> index 96910c625daa..53b6344a90d2 100644
> --- a/mm/memory.c
> +++ b/mm/memory.c
> @@ -817,19 +817,13 @@ static void print_bad_pte(struct vm_area_struct *vma, unsigned long addr,
>    * PFNMAP mappings in order to support COWable mappings.
>    *
>    */
> -#ifdef CONFIG_ARCH_HAS_PTE_SPECIAL
> -# define HAVE_PTE_SPECIAL 1
> -#else
> -# define HAVE_PTE_SPECIAL 0
> -#endif
>   struct page *_vm_normal_page(struct vm_area_struct *vma, unsigned long addr,
>   			     pte_t pte, bool with_public_device)
>   {
>   	unsigned long pfn = pte_pfn(pte);
>   
> -	if (HAVE_PTE_SPECIAL) {
> -		if (likely(!pte_special(pte)))
> -			goto check_pfn;
> +#ifdef CONFIG_ARCH_HAS_PTE_SPECIAL

Nit: Couldn't you use IS_ENABLED(CONFIG_ARCH_HAS_PTE_SPECIAL) within the 
existing code structure to avoid having to add these #ifdefs?

Robin.

> +	if (unlikely(pte_special(pte))) {
>   		if (vma->vm_ops && vma->vm_ops->find_special_page)
>   			return vma->vm_ops->find_special_page(vma, addr);
>   		if (vma->vm_flags & (VM_PFNMAP | VM_MIXEDMAP))
> @@ -862,7 +856,7 @@ struct page *_vm_normal_page(struct vm_area_struct *vma, unsigned long addr,
>   		return NULL;
>   	}
>   
> -	/* !HAVE_PTE_SPECIAL case follows: */
> +#else	/* CONFIG_ARCH_HAS_PTE_SPECIAL */
>   
>   	if (unlikely(vma->vm_flags & (VM_PFNMAP|VM_MIXEDMAP))) {
>   		if (vma->vm_flags & VM_MIXEDMAP) {
> @@ -881,7 +875,8 @@ struct page *_vm_normal_page(struct vm_area_struct *vma, unsigned long addr,
>   
>   	if (is_zero_pfn(pfn))
>   		return NULL;
> -check_pfn:
> +#endif /* CONFIG_ARCH_HAS_PTE_SPECIAL */
> +
>   	if (unlikely(pfn > highest_memmap_pfn)) {
>   		print_bad_pte(vma, addr, pte, NULL);
>   		return NULL;
> @@ -891,7 +886,7 @@ struct page *_vm_normal_page(struct vm_area_struct *vma, unsigned long addr,
>   	 * NOTE! We still have PageReserved() pages in the page tables.
>   	 * eg. VDSO mappings can cause them to exist.
>   	 */
> -out:
> +out: __maybe_unused
>   	return pfn_to_page(pfn);
>   }
>   
> @@ -904,7 +899,7 @@ struct page *vm_normal_page_pmd(struct vm_area_struct *vma, unsigned long addr,
>   	/*
>   	 * There is no pmd_special() but there may be special pmds, e.g.
>   	 * in a direct-access (dax) mapping, so let's just replicate the
> -	 * !HAVE_PTE_SPECIAL case from vm_normal_page() here.
> +	 * !CONFIG_ARCH_HAS_PTE_SPECIAL case from vm_normal_page() here.
>   	 */
>   	if (unlikely(vma->vm_flags & (VM_PFNMAP|VM_MIXEDMAP))) {
>   		if (vma->vm_flags & VM_MIXEDMAP) {
> @@ -1926,6 +1921,7 @@ static int __vm_insert_mixed(struct vm_area_struct *vma, unsigned long addr,
>   
>   	track_pfn_insert(vma, &pgprot, pfn);
>   
> +#ifndef CONFIG_ARCH_HAS_PTE_SPECIAL
>   	/*
>   	 * If we don't have pte special, then we have to use the pfn_valid()
>   	 * based VM_MIXEDMAP scheme (see vm_normal_page), and thus we *must*
> @@ -1933,7 +1929,7 @@ static int __vm_insert_mixed(struct vm_area_struct *vma, unsigned long addr,
>   	 * than insert_pfn).  If a zero_pfn were inserted into a VM_MIXEDMAP
>   	 * without pte special, it would there be refcounted as a normal page.
>   	 */
> -	if (!HAVE_PTE_SPECIAL && !pfn_t_devmap(pfn) && pfn_t_valid(pfn)) {
> +	if (!pfn_t_devmap(pfn) && pfn_t_valid(pfn)) {
>   		struct page *page;
>   
>   		/*
> @@ -1944,6 +1940,7 @@ static int __vm_insert_mixed(struct vm_area_struct *vma, unsigned long addr,
>   		page = pfn_to_page(pfn_t_to_pfn(pfn));
>   		return insert_page(vma, addr, page, pgprot);
>   	}
> +#endif
>   	return insert_pfn(vma, addr, pfn, pgprot, mkwrite);
>   }
>   
>