linux-kernel - [PATCH v3 03/11] mm/huge_memory: support huge zero folio in vmf_insert_folio

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Message-ID: <20250811112631.759341-4-david@redhat.com>
Date: Mon, 11 Aug 2025 13:26:23 +0200
From: David Hildenbrand <david@...hat.com>
To: linux-kernel@...r.kernel.org
Cc: linux-mm@...ck.org,
	xen-devel@...ts.xenproject.org,
	linux-fsdevel@...r.kernel.org,
	nvdimm@...ts.linux.dev,
	linuxppc-dev@...ts.ozlabs.org,
	David Hildenbrand <david@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Madhavan Srinivasan <maddy@...ux.ibm.com>,
	Michael Ellerman <mpe@...erman.id.au>,
	Nicholas Piggin <npiggin@...il.com>,
	Christophe Leroy <christophe.leroy@...roup.eu>,
	Juergen Gross <jgross@...e.com>,
	Stefano Stabellini <sstabellini@...nel.org>,
	Oleksandr Tyshchenko <oleksandr_tyshchenko@...m.com>,
	Dan Williams <dan.j.williams@...el.com>,
	Matthew Wilcox <willy@...radead.org>,
	Jan Kara <jack@...e.cz>,
	Alexander Viro <viro@...iv.linux.org.uk>,
	Christian Brauner <brauner@...nel.org>,
	Lorenzo Stoakes <lorenzo.stoakes@...cle.com>,
	"Liam R. Howlett" <Liam.Howlett@...cle.com>,
	Vlastimil Babka <vbabka@...e.cz>,
	Mike Rapoport <rppt@...nel.org>,
	Suren Baghdasaryan <surenb@...gle.com>,
	Michal Hocko <mhocko@...e.com>,
	Zi Yan <ziy@...dia.com>,
	Baolin Wang <baolin.wang@...ux.alibaba.com>,
	Nico Pache <npache@...hat.com>,
	Ryan Roberts <ryan.roberts@....com>,
	Dev Jain <dev.jain@....com>,
	Barry Song <baohua@...nel.org>,
	Jann Horn <jannh@...gle.com>,
	Pedro Falcato <pfalcato@...e.de>,
	Hugh Dickins <hughd@...gle.com>,
	Oscar Salvador <osalvador@...e.de>,
	Lance Yang <lance.yang@...ux.dev>,
	Wei Yang <richard.weiyang@...il.com>
Subject: [PATCH v3 03/11] mm/huge_memory: support huge zero folio in vmf_insert_folio_pmd()

Just like we do for vmf_insert_page_mkwrite() -> ... ->
insert_page_into_pte_locked() with the shared zeropage, support the
huge zero folio in vmf_insert_folio_pmd().

When (un)mapping the huge zero folio in page tables, we neither
adjust the refcount nor the mapcount, just like for the shared zeropage.

For now, the huge zero folio is not marked as special yet, although
vm_normal_page_pmd() really wants to treat it as special. We'll change
that next.

Reviewed-by: Oscar Salvador <osalvador@...e.de>
Reviewed-by: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
Reviewed-by: Wei Yang <richard.weiyang@...il.com>
Signed-off-by: David Hildenbrand <david@...hat.com>
---
 mm/huge_memory.c | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 7933791b75f4d..ec89e0607424e 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -1418,9 +1418,11 @@ static vm_fault_t insert_pmd(struct vm_area_struct *vma, unsigned long addr,
 	if (fop.is_folio) {
 		entry = folio_mk_pmd(fop.folio, vma->vm_page_prot);
 
-		folio_get(fop.folio);
-		folio_add_file_rmap_pmd(fop.folio, &fop.folio->page, vma);
-		add_mm_counter(mm, mm_counter_file(fop.folio), HPAGE_PMD_NR);
+		if (!is_huge_zero_folio(fop.folio)) {
+			folio_get(fop.folio);
+			folio_add_file_rmap_pmd(fop.folio, &fop.folio->page, vma);
+			add_mm_counter(mm, mm_counter_file(fop.folio), HPAGE_PMD_NR);
+		}
 	} else {
 		entry = pmd_mkhuge(pfn_pmd(fop.pfn, prot));
 		entry = pmd_mkspecial(entry);
-- 
2.50.1