Re: [PATCH v3 20/20] mm: stop maintaining the per-page mapcount of large folios (CONFIG_NO_PAGE_MAPCOUNT)

[Wei Yang <richard.weiyang@gmail.com>]

On Mon, Mar 03, 2025 at 05:30:13PM +0100, David Hildenbrand wrote:
[...]
>@@ -1678,6 +1726,22 @@ static __always_inline void __folio_remove_rmap(struct folio *folio,
> 		break;
> 	case RMAP_LEVEL_PMD:
> 	case RMAP_LEVEL_PUD:
>+		if (IS_ENABLED(CONFIG_NO_PAGE_MAPCOUNT)) {
>+			last = atomic_add_negative(-1, &folio->_entire_mapcount);
>+			if (level == RMAP_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);

Hi, David

Do you think this is better to be?

	partially_mapped = last && nr < nr_pmdmapped;

As commit 349994cf61e6 mentioned, we don't support partially mapped PUD-sized
folio yet.

Not sure what I missed here.

>+				nr = 0;
>+			}
>+			break;
>+		}
>+
> 		folio_dec_large_mapcount(folio, vma);
> 		last = atomic_add_negative(-1, &folio->_entire_mapcount);
> 		if (last) {
>-- 
>2.48.1
>

-- 
Wei Yang
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