linux-kernel - [PATCH RFC 07/14] fs/dax: use vmf_insert_folio

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Message-ID: <20250617154345.2494405-8-david@redhat.com>
Date: Tue, 17 Jun 2025 17:43:38 +0200
From: David Hildenbrand <david@...hat.com>
To: linux-kernel@...r.kernel.org
Cc: linux-fsdevel@...r.kernel.org,
	linux-mm@...ck.org,
	nvdimm@...ts.linux.dev,
	David Hildenbrand <david@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Juergen Gross <jgross@...e.com>,
	Stefano Stabellini <sstabellini@...nel.org>,
	Oleksandr Tyshchenko <oleksandr_tyshchenko@...m.com>,
	Dan Williams <dan.j.williams@...el.com>,
	Alistair Popple <apopple@...dia.com>,
	Matthew Wilcox <willy@...radead.org>,
	Jan Kara <jack@...e.cz>,
	Alexander Viro <viro@...iv.linux.org.uk>,
	Christian Brauner <brauner@...nel.org>,
	Zi Yan <ziy@...dia.com>,
	Baolin Wang <baolin.wang@...ux.alibaba.com>,
	Lorenzo Stoakes <lorenzo.stoakes@...cle.com>,
	"Liam R. Howlett" <Liam.Howlett@...cle.com>,
	Nico Pache <npache@...hat.com>,
	Ryan Roberts <ryan.roberts@....com>,
	Dev Jain <dev.jain@....com>,
	Barry Song <baohua@...nel.org>,
	Vlastimil Babka <vbabka@...e.cz>,
	Mike Rapoport <rppt@...nel.org>,
	Suren Baghdasaryan <surenb@...gle.com>,
	Michal Hocko <mhocko@...e.com>,
	Jann Horn <jannh@...gle.com>,
	Pedro Falcato <pfalcato@...e.de>
Subject: [PATCH RFC 07/14] fs/dax: use vmf_insert_folio_pmd() to insert the huge zero folio

Let's convert to vmf_insert_folio_pmd().

In the unlikely case there is already something mapped, we'll now still
call trace_dax_pmd_load_hole() and return VM_FAULT_NOPAGE.

That should probably be fine, no need to add special cases for that.

Signed-off-by: David Hildenbrand <david@...hat.com>
---
 fs/dax.c | 47 ++++++++++-------------------------------------
 1 file changed, 10 insertions(+), 37 deletions(-)

diff --git a/fs/dax.c b/fs/dax.c
index 4229513806bea..ae90706674a3f 100644
--- a/fs/dax.c
+++ b/fs/dax.c
@@ -1375,51 +1375,24 @@ static vm_fault_t dax_pmd_load_hole(struct xa_state *xas, struct vm_fault *vmf,
 		const struct iomap_iter *iter, void **entry)
 {
 	struct address_space *mapping = vmf->vma->vm_file->f_mapping;
-	unsigned long pmd_addr = vmf->address & PMD_MASK;
-	struct vm_area_struct *vma = vmf->vma;
 	struct inode *inode = mapping->host;
-	pgtable_t pgtable = NULL;
 	struct folio *zero_folio;
-	spinlock_t *ptl;
-	pmd_t pmd_entry;
-	unsigned long pfn;
+	vm_fault_t ret;
 
 	zero_folio = mm_get_huge_zero_folio(vmf->vma->vm_mm);
 
-	if (unlikely(!zero_folio))
-		goto fallback;
-
-	pfn = page_to_pfn(&zero_folio->page);
-	*entry = dax_insert_entry(xas, vmf, iter, *entry, pfn,
-				  DAX_PMD | DAX_ZERO_PAGE);
-
-	if (arch_needs_pgtable_deposit()) {
-		pgtable = pte_alloc_one(vma->vm_mm);
-		if (!pgtable)
-			return VM_FAULT_OOM;
-	}
-
-	ptl = pmd_lock(vmf->vma->vm_mm, vmf->pmd);
-	if (!pmd_none(*(vmf->pmd))) {
-		spin_unlock(ptl);
-		goto fallback;
+	if (unlikely(!zero_folio)) {
+		trace_dax_pmd_load_hole_fallback(inode, vmf, zero_folio, *entry);
+		return VM_FAULT_FALLBACK;
 	}
 
-	if (pgtable) {
-		pgtable_trans_huge_deposit(vma->vm_mm, vmf->pmd, pgtable);
-		mm_inc_nr_ptes(vma->vm_mm);
-	}
-	pmd_entry = folio_mk_pmd(zero_folio, vmf->vma->vm_page_prot);
-	set_pmd_at(vmf->vma->vm_mm, pmd_addr, vmf->pmd, pmd_entry);
-	spin_unlock(ptl);
-	trace_dax_pmd_load_hole(inode, vmf, zero_folio, *entry);
-	return VM_FAULT_NOPAGE;
+	*entry = dax_insert_entry(xas, vmf, iter, *entry, folio_pfn(zero_folio),
+				  DAX_PMD | DAX_ZERO_PAGE);
 
-fallback:
-	if (pgtable)
-		pte_free(vma->vm_mm, pgtable);
-	trace_dax_pmd_load_hole_fallback(inode, vmf, zero_folio, *entry);
-	return VM_FAULT_FALLBACK;
+	ret = vmf_insert_folio_pmd(vmf, zero_folio, false);
+	if (ret == VM_FAULT_NOPAGE)
+		trace_dax_pmd_load_hole(inode, vmf, zero_folio, *entry);
+	return ret;
 }
 #else
 static vm_fault_t dax_pmd_load_hole(struct xa_state *xas, struct vm_fault *vmf,
-- 
2.49.0