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

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Message-ID: <380d9bff359150f67ca6e0468f99ee746c1abdea.camel@infradead.org>
Date: Thu, 03 Apr 2025 08:15:41 +0100
From: David Woodhouse <dwmw2@...radead.org>
To: Mike Rapoport <rppt@...nel.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 Thu, 2025-04-03 at 08:07 +0100, David Woodhouse wrote:
> 
> I'll see if I can make it neater. I may drop the 'ret' variable
> completely and just turn the match clause into unlock-and-return-true.
> I *like* having a single unlock site. But I think I like simpler loop
> code more than that.

That's better (IMO).

And I note that pfn_valid() already doesn't follow the modern fetish
for having only one unlock site even when it makes the surrounding code
more complex to do so.

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;

	rcu_read_lock_sched();

	while (nr <= __highest_present_section_nr) {
		ms = __pfn_to_section(pfn);

		if (valid_section(ms) &&
		    (early_section(ms) || pfn_section_first_valid(ms, &pfn))) {
			*p_pfn = pfn;
			rcu_read_unlock_sched();
			return true;
		}

		/* Nothing left in this section? Skip to next section */
		nr++;
		pfn = section_nr_to_pfn(nr);
	}

	rcu_read_unlock_sched();

	return false;
}


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