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

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Message-ID: <Z-6XexJWecbxnrmK@kernel.org>
Date: Thu, 3 Apr 2025 17:13:15 +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 Thu, Apr 03, 2025 at 08:15:41AM +0100, David Woodhouse wrote:
> 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);

Maybe move the declaration here:

 	struct mem_section *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;
> }

-- 
Sincerely yours,
Mike.