filemap: allocate mapping_min_order folios in the page cache

filemap_create_folio() and do_read_cache_folio() were always allocating
folio of order 0. __filemap_get_folio was trying to allocate higher
order folios when fgp_flags had higher order hint set but it will default
to order 0 folio if higher order memory allocation fails.

Supporting mapping_min_order implies that we guarantee each folio in the
page cache has at least an order of mapping_min_order. When adding new
folios to the page cache we must also ensure the index used is aligned to
the mapping_min_order as the page cache requires the index to be aligned
to the order of the folio.

Co-developed-by: Luis Chamberlain <mcgrof@kernel.org>
Signed-off-by: Luis Chamberlain <mcgrof@kernel.org>
Signed-off-by: Pankaj Raghav <p.raghav@samsung.com>
Link: https://lore.kernel.org/r/20240822135018.1931258-3-kernel@pankajraghav.com
Tested-by: David Howells <dhowells@redhat.com>
Reviewed-by: Hannes Reinecke <hare@suse.de>
Reviewed-by: Darrick J. Wong <djwong@kernel.org>
Reviewed-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Reviewed-by: Daniel Gomez <da.gomez@samsung.com>
Reviewed-by: Dave Chinner <dchinner@redhat.com>
Signed-off-by: Christian Brauner <brauner@kernel.org>

1 files changed, 20 insertions, 0 deletions

diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
index c60025bb584c..4cc170949e9c 100644
--- a/include/linux/pagemap.h
+++ b/include/linux/pagemap.h
@@ -448,6 +448,26 @@ mapping_min_folio_order(const struct address_space *mapping)
 	return (mapping->flags & AS_FOLIO_ORDER_MIN_MASK) >> AS_FOLIO_ORDER_MIN;
 }
 
+static inline unsigned long
+mapping_min_folio_nrpages(struct address_space *mapping)
+{
+	return 1UL << mapping_min_folio_order(mapping);
+}
+
+/**
+ * mapping_align_index() - Align index for this mapping.
+ * @mapping: The address_space.
+ *
+ * The index of a folio must be naturally aligned.  If you are adding a
+ * new folio to the page cache and need to know what index to give it,
+ * call this function.
+ */
+static inline pgoff_t mapping_align_index(struct address_space *mapping,
+					  pgoff_t index)
+{
+	return round_down(index, mapping_min_folio_nrpages(mapping));
+}
+
 /*
  * Large folio support currently depends on THP.  These dependencies are
  * being worked on but are not yet fixed.