linux-kernel - Re: [PATCH v6 11/15] mm: define clear_pages(), clear_user

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Message-ID: <643f5482-cd34-4534-8cd8-69f32482bc27@redhat.com>
Date: Tue, 2 Sep 2025 22:16:40 +0200
From: David Hildenbrand <david@...hat.com>
To: Ankur Arora <ankur.a.arora@...cle.com>, linux-kernel@...r.kernel.org,
 linux-mm@...ck.org, x86@...nel.org
Cc: akpm@...ux-foundation.org, bp@...en8.de, dave.hansen@...ux.intel.com,
 hpa@...or.com, mingo@...hat.com, mjguzik@...il.com, luto@...nel.org,
 peterz@...radead.org, acme@...nel.org, namhyung@...nel.org,
 tglx@...utronix.de, willy@...radead.org, raghavendra.kt@....com,
 boris.ostrovsky@...cle.com, konrad.wilk@...cle.com
Subject: Re: [PATCH v6 11/15] mm: define clear_pages(), clear_user_pages()

On 02.09.25 10:08, Ankur Arora wrote:
> Define fallback versions of clear_pages(), clear_user_pages().
> 
> In absence of architectural primitives, these just do straight clearing
> sequentially.
> 
> Signed-off-by: Ankur Arora <ankur.a.arora@...cle.com>
> ---
>   include/linux/mm.h | 32 ++++++++++++++++++++++++++++++++
>   1 file changed, 32 insertions(+)
> 
> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index 1ae97a0b8ec7..b8c3f265b497 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -3768,6 +3768,38 @@ static inline void clear_page_guard(struct zone *zone, struct page *page,
>   				unsigned int order) {}
>   #endif	/* CONFIG_DEBUG_PAGEALLOC */
>   
> +#ifndef ARCH_PAGE_CONTIG_NR
> +#define PAGE_CONTIG_NR	1
> +#else
> +#define PAGE_CONTIG_NR	ARCH_PAGE_CONTIG_NR
> +#endif
> +

These likely don't belong into this aptch :)

> +#ifndef clear_pages
> +/*

/**

for proper kernel doc

> + * clear_pages() - clear kernel page range.
> + * @addr: start address of page range
> + * @npages: number of pages
> + *
> + * Assumes that (@addr, +@...ges) references a kernel region.
> + * Like clear_page(), this does absolutely no exception handling.
> + */
> +static inline void clear_pages(void *addr, unsigned int npages)
> +{
> +	for (int i = 0; i < npages; i++)
> +		clear_page(addr + i * PAGE_SIZE);

If we know that we will clear at least one page (which we can document)

do {
	clear_page(addr);
	addr += PAGE_SIZE;
} while (--npages);

Similarly for the case below.

> +}
> +#endif
> +
> +#ifndef clear_user_pages

Can we add kernel doc here as well?

> +static inline void clear_user_pages(void *addr, unsigned long vaddr,
> +				    struct page *pg, unsigned int npages)
> +{
> +	for (int i = 0; i < npages; i++)
> +		clear_user_page(addr + i * PAGE_SIZE,
> +				vaddr + i * PAGE_SIZE, pg + i);
> +}
> +#endif
> +
>   #ifdef __HAVE_ARCH_GATE_AREA
>   extern struct vm_area_struct *get_gate_vma(struct mm_struct *mm);
>   extern int in_gate_area_no_mm(unsigned long addr);


-- 
Cheers

David / dhildenb