Re: [RFC PATCH 3/3] mm: Implement for_each_valid_pfn() for CONFIG_SPARSEMEM

[Mike Rapoport <rppt@kernel.org>]

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.