[RFC 03/23] filemap: add folio with at least mapping_min_order in __filemap_get_folio

[Pankaj Raghav]

From: Pankaj Raghav <p.raghav@xxxxxxxxxxx>

__filemap_get_folio() with FGP_CREAT should allocate at least folio of
filemap's min_order set using folio_set_mapping_orders().

A higher order folio than min_order by definition is a multiple of the
min_order. If an index is aligned to an order higher than a min_order, it
will also be aligned to the min order.

Signed-off-by: Pankaj Raghav <p.raghav@xxxxxxxxxxx>
---
 mm/filemap.c | 12 +++++++++++-
 1 file changed, 11 insertions(+), 1 deletion(-)

diff --git a/mm/filemap.c b/mm/filemap.c
index 8962d1255905..b1ce63143df5 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -1862,6 +1862,10 @@ struct folio *__filemap_get_folio(struct address_space *mapping, pgoff_t index,
 		fgf_t fgp_flags, gfp_t gfp)
 {
 	struct folio *folio;
+	int min_order = mapping_min_folio_order(mapping);
+	int nr_of_pages = (1U << min_order);
+
+	index = round_down(index, nr_of_pages);
 
 repeat:
 	folio = filemap_get_entry(mapping, index);
@@ -1929,8 +1933,14 @@ struct folio *__filemap_get_folio(struct address_space *mapping, pgoff_t index,
 			err = -ENOMEM;
 			if (order == 1)
 				order = 0;
+			if (order < min_order)
+				order = min_order;
 			if (order > 0)
 				alloc_gfp |= __GFP_NORETRY | __GFP_NOWARN;
+
+			if (min_order)
+				VM_BUG_ON(index & ((1UL << order) - 1));
+
 			folio = filemap_alloc_folio(alloc_gfp, order);
 			if (!folio)
 				continue;
@@ -1944,7 +1954,7 @@ struct folio *__filemap_get_folio(struct address_space *mapping, pgoff_t index,
 				break;
 			folio_put(folio);
 			folio = NULL;
-		} while (order-- > 0);
+		} while (order-- > min_order);
 
 		if (err == -EEXIST)
 			goto repeat;
-- 
2.40.1