linux-kernel - Re: [RFC PATCH v2 2/7] mm: Implement for_each_valid_pfn() for CONFIG

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Message-ID: <Z_N2nyKYBOf2PoBz@kernel.org>
Date: Mon, 7 Apr 2025 09:54:23 +0300
From: Mike Rapoport <rppt@...nel.org>
To: David Woodhouse <dwmw2@...radead.org>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
	"Sauerwein, David" <dssauerw@...zon.de>,
	Anshuman Khandual <anshuman.khandual@....com>,
	Ard Biesheuvel <ardb@...nel.org>,
	Catalin Marinas <catalin.marinas@....com>,
	David Hildenbrand <david@...hat.com>, Marc Zyngier <maz@...nel.org>,
	Mark Rutland <mark.rutland@....com>,
	Mike Rapoport <rppt@...ux.ibm.com>, Will Deacon <will@...nel.org>,
	kvmarm@...ts.cs.columbia.edu, linux-arm-kernel@...ts.infradead.org,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [RFC PATCH v2 2/7] mm: Implement for_each_valid_pfn() for
 CONFIG_FLATMEM

On Fri, Apr 04, 2025 at 04:59:54PM +0100, David Woodhouse wrote:
> From: David Woodhouse <dwmw@...zon.co.uk>
> 
> In the FLATMEM case, the default pfn_valid() just checks that the PFN is
> within the range [ ARCH_PFN_OFFSET .. ARCH_PFN_OFFSET + max_mapnr ).
> 
> The for_each_valid_pfn() function can therefore be a simple for() loop
> using those as min/max respectively.
> 
> Signed-off-by: David Woodhouse <dwmw@...zon.co.uk>
> Reviewed-by: Mike Rapoport (Microsoft) <rppt@...nel.org>
> ---
>  include/asm-generic/memory_model.h | 26 +++++++++++++++++++++++++-
>  1 file changed, 25 insertions(+), 1 deletion(-)
> 
> diff --git a/include/asm-generic/memory_model.h b/include/asm-generic/memory_model.h
> index a3b5029aebbd..044536da3390 100644
> --- a/include/asm-generic/memory_model.h
> +++ b/include/asm-generic/memory_model.h
> @@ -30,7 +30,31 @@ static inline int pfn_valid(unsigned long pfn)
>  	return pfn >= pfn_offset && (pfn - pfn_offset) < max_mapnr;
>  }
>  #define pfn_valid pfn_valid
> -#endif
> +
> +static inline bool first_valid_pfn(unsigned long *pfn)

This is now different from SPARSEMEM version. Do we need it at all?

> +{
> +	/* avoid <linux/mm.h> include hell */
>
> +	extern unsigned long max_mapnr;
> +	unsigned long pfn_offset = ARCH_PFN_OFFSET;
> +
> +	if (*pfn < pfn_offset) {
> +		*pfn = pfn_offset;
> +		return true;
> +	}
> +
> +	if ((*pfn - pfn_offset) < max_mapnr)
> +		return true;
> +
> +	return false;
> +}
> +
> +#ifndef for_each_valid_pfn
> +#define for_each_valid_pfn(pfn, start_pfn, end_pfn)			       \
> +	for (pfn = max_t(unsigned long, start_pfn, ARCH_PFN_OFFSET);	\
> +	     pfn < min_t(unsigned long, end_pfn, ARCH_PFN_OFFSET + max_mapnr); \
> +			 pfn++)
> +#endif /* for_each_valid_pfn */
> +#endif /* valid_pfn */
>  
>  #elif defined(CONFIG_SPARSEMEM_VMEMMAP)
>  
> -- 
> 2.49.0
> 

-- 
Sincerely yours,
Mike.