Re: [PATCH v2] mm/swapops,rmap: remove should-never-be-compiled codes.

[Andrew Morton <akpm@linux-foundation.org>]

On Tue, 30 Dec 2025 21:01:10 +0800 Wale Zhang <wale.zhang.ftd@gmail.com> wrote:

> mm/swapops,rmap: remove should-never-be-compiled codes, included
> folio_add_return_large_mapcount(), folio_sub_return_large_mapcount(),
> set_pmd_migration_entry() and remove_migration_pmd().

Please provide a reason for making this change.

>
> ...
>
> @@ -1264,22 +1262,21 @@ static __always_inline void __folio_add_rmap(struct folio *folio,
>  			nr = first;
>  
>  		folio_add_large_mapcount(folio, orig_nr_pages, vma);
> +#endif
>  		break;
>  	case PGTABLE_LEVEL_PMD:
>  	case PGTABLE_LEVEL_PUD:
>  		first = atomic_inc_and_test(&folio->_entire_mapcount);
> -		if (IS_ENABLED(CONFIG_NO_PAGE_MAPCOUNT)) {
> -			if (level == PGTABLE_LEVEL_PMD && first)
> -				nr_pmdmapped = folio_large_nr_pages(folio);
> -			nr = folio_inc_return_large_mapcount(folio, vma);
> -			if (nr == 1)
> -				/* Was completely unmapped. */
> -				nr = folio_large_nr_pages(folio);
> -			else
> -				nr = 0;
> -			break;
> -		}
> -
> +#ifdef CONFIG_NO_PAGE_MAPCOUNT
> +		if (level == PGTABLE_LEVEL_PMD && first)
> +			nr_pmdmapped = folio_large_nr_pages(folio);
> +		nr = folio_inc_return_large_mapcount(folio, vma);
> +		if (nr == 1)
> +			/* Was completely unmapped. */
> +			nr = folio_large_nr_pages(folio);
> +		else
> +			nr = 0;
> +#else

Changes like this made the code unpleasant to read and harder to work
on.  What do we get in return for this?