linux-kernel - Re: [RFC PATCH 3/3] mm: Implement for_each_valid_pfn() for CONFIG

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Message-ID: <Z-4phOInXZlxFwk9@kernel.org>
Date: Thu, 3 Apr 2025 09:24:04 +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 3/3] mm: Implement for_each_valid_pfn() for
 CONFIG_SPARSEMEM

On Wed, Apr 02, 2025 at 09:18:41PM +0100, David Woodhouse wrote:
> From: David Woodhouse <dwmw@...zon.co.uk>
> 
> Introduce a pfn_first_valid() helper which takes a pointer to the PFN and
> updates it to point to the first valid PFN starting from that point, and
> returns true if a valid PFN was found.
> 
> This largely mirrors pfn_valid(), calling into a pfn_section_first_valid()
> helper which is trivial for the !CONFIG_SPARSEMEM_VMEMMAP case, and in
> the VMEMMAP case will skip to the next subsection as needed.
> 
> Signed-off-by: David Woodhouse <dwmw@...zon.co.uk>

Reviewed-by: Mike Rapoport (Microsoft) <rppt@...nel.org>

with a small nit below

> +static inline bool first_valid_pfn(unsigned long *p_pfn)
> +{
> +	unsigned long pfn = *p_pfn;
> +	unsigned long nr = pfn_to_section_nr(pfn);
> +	struct mem_section *ms;
> +	bool ret = false;
> +
> +	ms = __pfn_to_section(pfn);
> +
> +	rcu_read_lock_sched();
> +
> +	while (!ret && nr <= __highest_present_section_nr) {

This could be just for(;;), we anyway break when ret becomes true or we get
past last present section.

> +		if (valid_section(ms) &&
> +		    (early_section(ms) || pfn_section_first_valid(ms, &pfn))) {
> +			ret = true;
> +			break;
> +		}
> +
> +		nr++;
> +		if (nr > __highest_present_section_nr)
> +			break;
> +
> +		pfn = section_nr_to_pfn(nr);
> +		ms = __pfn_to_section(pfn);
> +	}
> +
> +	rcu_read_unlock_sched();
> +
> +	*p_pfn = pfn;
> +
> +	return ret;
> +}
> +
> +#define for_each_valid_pfn(_pfn, _start_pfn, _end_pfn)	       \
> +	for ((_pfn) = (_start_pfn);			       \
> +	     first_valid_pfn(&(_pfn)) && (_pfn) < (_end_pfn);  \
> +	     (_pfn)++)
> +
>  #endif
>  
>  static inline int pfn_in_present_section(unsigned long pfn)
> -- 
> 2.49.0
> 

-- 
Sincerely yours,
Mike.