From: Pankaj Raghav <p.raghav@xxxxxxxxxxx>
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.
Co-developed-by: David Hildenbrand <david@xxxxxxxxxx>
Signed-off-by: David Hildenbrand <david@xxxxxxxxxx>
Signed-off-by: Pankaj Raghav <p.raghav@xxxxxxxxxxx>
---
include/linux/huge_mm.h | 22 ++++++++++++++++++++++
1 file changed, 22 insertions(+)
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 */
--
2.49.0
