linux-kernel - Re: [RFC 2/2] arm64/mm: Enable device memory allocation and free for vmemmap mapping

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Date:   Wed, 31 Jul 2019 17:11:04 +0100
From:   Will Deacon <will@...nel.org>
To:     Anshuman Khandual <anshuman.khandual@....com>
Cc:     linux-mm@...ck.org, Mark Rutland <mark.rutland@....com>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will.deacon@....com>,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org
Subject: Re: [RFC 2/2] arm64/mm: Enable device memory allocation and free for
 vmemmap mapping

On Fri, Jun 28, 2019 at 10:14:43AM +0530, Anshuman Khandual wrote:
> This enables vmemmap_populate() and vmemmap_free() functions to incorporate
> struct vmem_altmap based device memory allocation and free requests. With
> this device memory with specific atlmap configuration can be hot plugged
> and hot removed as ZONE_DEVICE memory on arm64 platforms.
> 
> Cc: Catalin Marinas <catalin.marinas@....com>
> Cc: Will Deacon <will.deacon@....com>
> Cc: Mark Rutland <mark.rutland@....com>
> Cc: linux-arm-kernel@...ts.infradead.org
> Cc: linux-kernel@...r.kernel.org
> 
> Signed-off-by: Anshuman Khandual <anshuman.khandual@....com>
> ---
>  arch/arm64/mm/mmu.c | 57 ++++++++++++++++++++++++++++++++++-------------------
>  1 file changed, 37 insertions(+), 20 deletions(-)
> 
> diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c
> index 39e18d1..8867bbd 100644
> --- a/arch/arm64/mm/mmu.c
> +++ b/arch/arm64/mm/mmu.c
> @@ -735,15 +735,26 @@ int kern_addr_valid(unsigned long addr)
>  }
>  
>  #ifdef CONFIG_MEMORY_HOTPLUG
> -static void free_hotplug_page_range(struct page *page, size_t size)
> +static void free_hotplug_page_range(struct page *page, size_t size,
> +				    struct vmem_altmap *altmap)
>  {
> -	WARN_ON(!page || PageReserved(page));
> -	free_pages((unsigned long)page_address(page), get_order(size));
> +	if (altmap) {
> +		/*
> +		 * vmemmap_populate() creates vmemmap mapping either at pte
> +		 * or pmd level. Unmapping request at any other level would
> +		 * be a problem.
> +		 */
> +		WARN_ON((size != PAGE_SIZE) && (size != PMD_SIZE));
> +		vmem_altmap_free(altmap, size >> PAGE_SHIFT);
> +	} else {
> +		WARN_ON(!page || PageReserved(page));
> +		free_pages((unsigned long)page_address(page), get_order(size));
> +	}
>  }
>  
>  static void free_hotplug_pgtable_page(struct page *page)
>  {
> -	free_hotplug_page_range(page, PAGE_SIZE);
> +	free_hotplug_page_range(page, PAGE_SIZE, NULL);
>  }
>  
>  static void free_pte_table(pmd_t *pmdp, unsigned long addr)
> @@ -807,7 +818,8 @@ static void free_pud_table(pgd_t *pgdp, unsigned long addr)
>  }
>  
>  static void unmap_hotplug_pte_range(pmd_t *pmdp, unsigned long addr,
> -				    unsigned long end, bool sparse_vmap)
> +				    unsigned long end, bool sparse_vmap,
> +				    struct vmem_altmap *altmap)

Do you still need the sparse_vmap parameter, or can you just pass a NULL
altmap pointer when sparse_vmap is false?

Will