Commit b0f86aae authored by David Hildenbrand's avatar David Hildenbrand Committed by Andrew Morton
Browse files

fs/dax: use vmf_insert_folio_pmd() to insert the huge zero folio 

Let's convert to vmf_insert_folio_pmd().

There is a theoretical change in behavior: in the unlikely case there is
already something mapped, we'll now still call trace_dax_pmd_load_hole()
and return VM_FAULT_NOPAGE.

Previously, we would have returned VM_FAULT_FALLBACK, and the caller would
have zapped the PMD to try a PTE fault.

However, that behavior was different to other PTE+PMD faults, when there
would already be something mapped, and it's not even clear if it could be
triggered.

Assuming the huge zero folio is already mapped, all good, no need to
fallback to PTEs.

Assuming there is already a leaf page table ...  the behavior would be
just like when trying to insert a PMD mapping a folio through
dax_fault_iter()->vmf_insert_folio_pmd().

Assuming there is already something else mapped as PMD?  It sounds like a
BUG, and the behavior would be just like when trying to insert a PMD
mapping a folio through dax_fault_iter()->vmf_insert_folio_pmd().

So, it sounds reasonable to not handle huge zero folios differently to
inserting PMDs mapping folios when there already is something mapped.

Link: https://lkml.kernel.org/r/20250811112631.759341-5-david@redhat.com


Signed-off-by: default avatarDavid Hildenbrand <david@redhat.com>
Reviewed-by: default avatarAlistair Popple <apopple@nvidia.com>
Reviewed-by: default avatarLorenzo Stoakes <lorenzo.stoakes@oracle.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Baolin Wang <baolin.wang@linux.alibaba.com>
Cc: Barry Song <baohua@kernel.org>
Cc: Christian Brauner <brauner@kernel.org>
Cc: Christophe Leroy <christophe.leroy@csgroup.eu>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: David Vrabel <david.vrabel@citrix.com>
Cc: Dev Jain <dev.jain@arm.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Jan Kara <jack@suse.cz>
Cc: Jann Horn <jannh@google.com>
Cc: Juegren Gross <jgross@suse.com>
Cc: Lance Yang <lance.yang@linux.dev>
Cc: Liam Howlett <liam.howlett@oracle.com>
Cc: Madhavan Srinivasan <maddy@linux.ibm.com>
Cc: Mariano Pache <npache@redhat.com>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Mike Rapoport <rppt@kernel.org>
Cc: Nicholas Piggin <npiggin@gmail.com>
Cc: Oleksandr Tyshchenko <oleksandr_tyshchenko@epam.com>
Cc: Oscar Salvador <osalvador@suse.de>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Cc: Stefano Stabellini <sstabellini@kernel.org>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Wei Yang <richard.weiyang@gmail.com>
Cc: Zi Yan <ziy@nvidia.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
parent 5528ef06

fs/dax.c

+10 −37
Original line number Diff line number Diff line
@@ -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;

	if (unlikely(!zero_folio)) {

		trace_dax_pmd_load_hole_fallback(inode, vmf, zero_folio, *entry);

		return VM_FAULT_FALLBACK;

	}



	ptl = pmd_lock(vmf->vma->vm_mm, vmf->pmd);

	if (!pmd_none(*(vmf->pmd))) {

		spin_unlock(ptl);

		goto fallback;

	}

	*entry = dax_insert_entry(xas, vmf, iter, *entry, folio_pfn(zero_folio),

				  DAX_PMD | DAX_ZERO_PAGE);



	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);

	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 VM_FAULT_NOPAGE;



fallback:

	if (pgtable)

		pte_free(vma->vm_mm, pgtable);

	trace_dax_pmd_load_hole_fallback(inode, vmf, zero_folio, *entry);

	return VM_FAULT_FALLBACK;

	return ret;

}

#else

static vm_fault_t dax_pmd_load_hole(struct xa_state *xas, struct vm_fault *vmf,