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

[Barry Song <21cnbao@gmail.com>]

On Wed, Dec 31, 2025 at 8:50 AM David Hildenbrand (Red Hat)
<david@kernel.org> wrote:
>
>
> > -                     break;
> > +#ifdef CONFIG_NO_PAGE_MAPCOUNT
> > +             last = atomic_add_negative(-1, &folio->_entire_mapcount);
> > +             if (level == PGTABLE_LEVEL_PMD && last)
> > +                     nr_pmdmapped = folio_large_nr_pages(folio);
> > +             nr = folio_dec_return_large_mapcount(folio, vma);
> > +             if (!nr) {
> > +                     /* Now completely unmapped. */
> > +                     nr = folio_large_nr_pages(folio);
> > +             } else {
> > +                     partially_mapped = last &&
> > +                             nr < folio_large_nr_pages(folio);
> > +                     nr = 0;
>
> The whole code was written to avoid ifdefs.

The #ifdefs are only for -O0 builds, which are never a
mainline requirement. However, dropping functions that
contain nothing but a BUILD_BUG() seems reasonable?

If those functions were actually required, the compiler
would fail anyway. In that case, there doesn’t seem to be
much value in keeping wrapper functions whose sole purpose
is to contain a single BUILD_BUG().

Thanks
Barry