[v4,1/2] filemap: add helper mapping_max_folio_size()

Commit Message

Xu Yang May 21, 2024, 11:36 a.m. UTC

Add mapping_max_folio_size() to get the maximum folio size for this
pagecache mapping.

Reviewed-by: Darrick J. Wong <[e-mail]>
Signed-off-by: Xu Yang <[e-mail]>

---
Changes in v4:
 - split the mapping_max_folio_size() from v3
 - adjust mapping_max_folio_size() comment
 - add Rb tag
---
 include/linux/pagemap.h | 34 +++++++++++++++++++++-------------
 1 file changed, 21 insertions(+), 13 deletions(-)

Patch

diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
index c5e33e2ca48a..d43cf36bb68b 100644
--- a/include/linux/pagemap.h
+++ b/include/linux/pagemap.h
@@ -346,6 +346,19 @@  static inline void mapping_set_gfp_mask(struct address_space *m, gfp_t mask)
 	m->gfp_mask = mask;
 }
 
+/*
+ * There are some parts of the kernel which assume that PMD entries
+ * are exactly HPAGE_PMD_ORDER.  Those should be fixed, but until then,
+ * limit the maximum allocation order to PMD size.  I'm not aware of any
+ * assumptions about maximum order if THP are disabled, but 8 seems like
+ * a good order (that's 1MB if you're using 4kB pages)
+ */
+#ifdef CONFIG_TRANSPARENT_HUGEPAGE
+#define MAX_PAGECACHE_ORDER	HPAGE_PMD_ORDER
+#else
+#define MAX_PAGECACHE_ORDER	8
+#endif
+
 /**
  * mapping_set_large_folios() - Indicate the file supports large folios.
  * @mapping: The file.
@@ -372,6 +385,14 @@  static inline bool mapping_large_folio_support(struct address_space *mapping)
 		test_bit(AS_LARGE_FOLIO_SUPPORT, &mapping->flags);
 }
 
+/* Return the maximum folio size for this pagecache mapping, in bytes. */
+static inline size_t mapping_max_folio_size(struct address_space *mapping)
+{
+	if (mapping_large_folio_support(mapping))
+		return PAGE_SIZE << MAX_PAGECACHE_ORDER;
+	return PAGE_SIZE;
+}
+
 static inline int filemap_nr_thps(struct address_space *mapping)
 {
 #ifdef CONFIG_READ_ONLY_THP_FOR_FS
@@ -530,19 +551,6 @@  static inline void *detach_page_private(struct page *page)
 	return folio_detach_private(page_folio(page));
 }
 
-/*
- * There are some parts of the kernel which assume that PMD entries
- * are exactly HPAGE_PMD_ORDER.  Those should be fixed, but until then,
- * limit the maximum allocation order to PMD size.  I'm not aware of any
- * assumptions about maximum order if THP are disabled, but 8 seems like
- * a good order (that's 1MB if you're using 4kB pages)
- */
-#ifdef CONFIG_TRANSPARENT_HUGEPAGE
-#define MAX_PAGECACHE_ORDER	HPAGE_PMD_ORDER
-#else
-#define MAX_PAGECACHE_ORDER	8
-#endif
-
 #ifdef CONFIG_NUMA
 struct folio *filemap_alloc_folio(gfp_t gfp, unsigned int order);
 #else