mm: add largest_zero_folio() routine

The callers of mm_get_huge_zero_folio() have access to a mm struct and the
lifetime of the huge_zero_folio is tied to the lifetime of the mm struct.

largest_zero_folio() will give access to huge_zero_folio when
PERSISTENT_HUGE_ZERO_FOLIO config option is enabled for callers that do
not want to tie the lifetime to a mm struct.  This is very useful for
filesystem and block layers where the request completions can be async and
there is no guarantee on the mm struct lifetime.

This function will return a ZERO_PAGE folio if PERSISTENT_HUGE_ZERO_FOLIO
is disabled or if we failed to allocate a huge_zero_folio during early
init.

Link: https://lkml.kernel.org/r/20250811084113.647267-5-kernel@pankajraghav.com
Signed-off-by: David Hildenbrand <david@redhat.com>
Signed-off-by: Pankaj Raghav <p.raghav@samsung.com>
Reviewed-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Co-developed-by: David Hildenbrand <david@redhat.com>
Reviewed-by: Hannes Reinecke <hare@suse.de>
Cc: Baolin Wang <baolin.wang@linux.alibaba.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: "Darrick J. Wong" <djwong@kernel.org>
Cc: Dev Jain <dev.jain@arm.com>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Liam Howlett <liam.howlett@oracle.com>
Cc: Luis Chamberalin <mcgrof@kernel.org>
Cc: Mariano Pache <npache@redhat.com>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Mike Rapoport <rppt@kernel.org>
Cc: "Ritesh Harjani (IBM)" <ritesh.list@gmail.com>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Thomas Gleinxer <tglx@linutronix.de>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Zi Yan <ziy@nvidia.com>
Cc: Kiryl Shutsemau <kirill@shutemov.name>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

1 files changed, 22 insertions, 0 deletions

diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h
index bd547857c6c1..14d424830fa8 100644
--- a/include/linux/huge_mm.h
+++ b/include/linux/huge_mm.h
@@ -714,4 +714,26 @@ static inline int split_folio_to_order(struct folio *folio, int new_order)
 	return split_folio_to_list_to_order(folio, NULL, new_order);
 }
 
+/**
+ * largest_zero_folio - Get the largest zero size folio available
+ *
+ * This function shall be used when mm_get_huge_zero_folio() cannot be
+ * used as there is no appropriate mm lifetime to tie the huge zero folio
+ * from the caller.
+ *
+ * Deduce the size of the folio with folio_size instead of assuming the
+ * folio size.
+ *
+ * Return: pointer to PMD sized zero folio if CONFIG_PERSISTENT_HUGE_ZERO_FOLIO
+ * is enabled or a single page sized zero folio
+ */
+static inline struct folio *largest_zero_folio(void)
+{
+	struct folio *folio = get_persistent_huge_zero_folio();
+
+	if (folio)
+		return folio;
+
+	return page_folio(ZERO_PAGE(0));
+}
 #endif /* _LINUX_HUGE_MM_H */