We need filesystems to be able to communicate acceptable folio sizes
to the pagecache for a variety of uses (e.g. large block sizes).
Support a range of folio sizes between order-0 and order-31.

Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Co-developed-by: Pankaj Raghav <redacted>
Signed-off-by: Pankaj Raghav <redacted>
Reviewed-by: Darrick J. Wong <djwong@kernel.org>
Reviewed-by: Hannes Reinecke <hare@suse.de>
---
For this version, I fixed the TODO that the maximum folio size was not
being honoured.  I made some other changes too like adding const, moving
the location of the constants, checking CONFIG_TRANSPARENT_HUGEPAGE, and
dropping some of the functions which aren't needed until later patches.
(They can be added in the commits that need them).  Also rebased against
current Linus tree, so MAX_PAGECACHE_ORDER no longer needs to be moved).

  include/linux/pagemap.h | 81 +++++++++++++++++++++++++++++++++++------
  mm/filemap.c            |  6 +--
  mm/readahead.c          |  4 +-
  3 files changed, 73 insertions(+), 18 deletions(-)

diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
index 1ed9274a0deb..c6aaceed0de6 100644
--- a/include/linux/pagemap.h
+++ b/include/linux/pagemap.h

@@ -204,13 +204,18 @@ enum mapping_flags {
  	AS_EXITING	= 4, 	/* final truncate in progress */
  	/* writeback related tags are not used */
  	AS_NO_WRITEBACK_TAGS = 5,
-	AS_LARGE_FOLIO_SUPPORT = 6,
-	AS_RELEASE_ALWAYS,	/* Call ->release_folio(), even if no private data */
-	AS_STABLE_WRITES,	/* must wait for writeback before modifying
+	AS_RELEASE_ALWAYS = 6,	/* Call ->release_folio(), even if no private data */
+	AS_STABLE_WRITES = 7,	/* must wait for writeback before modifying
  				   folio contents */
-	AS_UNMOVABLE,		/* The mapping cannot be moved, ever */
+	AS_UNMOVABLE = 8,	/* The mapping cannot be moved, ever */
+	AS_FOLIO_ORDER_MIN = 16,
+	AS_FOLIO_ORDER_MAX = 21, /* Bits 16-25 are used for FOLIO_ORDER */
  };
  
+#define AS_FOLIO_ORDER_MIN_MASK 0x001f0000
+#define AS_FOLIO_ORDER_MAX_MASK 0x03e00000
+#define AS_FOLIO_ORDER_MASK (AS_FOLIO_ORDER_MIN_MASK | AS_FOLIO_ORDER_MAX_MASK)
+
  /**
   * mapping_set_error - record a writeback error in the address_space
   * @mapping: the mapping in which an error should be set

@@ -359,9 +364,48 @@ static inline void mapping_set_gfp_mask(struct address_space *m, gfp_t mask)
  #define MAX_PAGECACHE_ORDER	8
  #endif
  
+/*
+ * mapping_set_folio_order_range() - Set the orders supported by a file.
+ * @mapping: The address space of the file.
+ * @min: Minimum folio order (between 0-MAX_PAGECACHE_ORDER inclusive).
+ * @max: Maximum folio order (between @min-MAX_PAGECACHE_ORDER inclusive).
+ *
+ * The filesystem should call this function in its inode constructor to
+ * indicate which base size (min) and maximum size (max) of folio the VFS
+ * can use to cache the contents of the file.  This should only be used
+ * if the filesystem needs special handling of folio sizes (ie there is
+ * something the core cannot know).
+ * Do not tune it based on, eg, i_size.
+ *
+ * Context: This should not be called while the inode is active as it
+ * is non-atomic.
+ */
+static inline void mapping_set_folio_order_range(struct address_space *mapping,
+		unsigned int min, unsigned int max)
+{
+	if (IS_ENABLED(CONFIG_TRANSPARENT_HUGEPAGE))
+		return;
+