[RFC v2 03/14] filemap: use mapping_min_order while allocating folios

["Pankaj Raghav (Samsung)" <kernel@xxxxxxxxxxxxxxxx>]

From: Pankaj Raghav <p.raghav@xxxxxxxxxxx>

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.

As we bring the notion of mapping_min_order, make sure these functions
allocate at least folio of mapping_min_order as we need to guarantee it
in the page cache.

Add some additional VM_BUG_ON() in page_cache_delete[batch] and
__filemap_add_folio to catch errors where we delete or add folios that
has order less than min_order.

Signed-off-by: Pankaj Raghav <p.raghav@xxxxxxxxxxx>
Signed-off-by: Luis Chamberlain <mcgrof@xxxxxxxxxx>
---
 mm/filemap.c | 25 +++++++++++++++++++++----
 1 file changed, 21 insertions(+), 4 deletions(-)

diff --git a/mm/filemap.c b/mm/filemap.c
index 323a8e169581..7a6e15c47150 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -127,6 +127,7 @@
 static void page_cache_delete(struct address_space *mapping,
 				   struct folio *folio, void *shadow)
 {
+	unsigned int min_order = mapping_min_folio_order(mapping);
 	XA_STATE(xas, &mapping->i_pages, folio->index);
 	long nr = 1;
 
@@ -135,6 +136,7 @@ static void page_cache_delete(struct address_space *mapping,
 	xas_set_order(&xas, folio->index, folio_order(folio));
 	nr = folio_nr_pages(folio);
 
+	VM_BUG_ON_FOLIO(folio_order(folio) < min_order, folio);
 	VM_BUG_ON_FOLIO(!folio_test_locked(folio), folio);
 
 	xas_store(&xas, shadow);
@@ -277,6 +279,7 @@ void filemap_remove_folio(struct folio *folio)
 static void page_cache_delete_batch(struct address_space *mapping,
 			     struct folio_batch *fbatch)
 {
+	unsigned int min_order = mapping_min_folio_order(mapping);
 	XA_STATE(xas, &mapping->i_pages, fbatch->folios[0]->index);
 	long total_pages = 0;
 	int i = 0;
@@ -305,6 +308,7 @@ static void page_cache_delete_batch(struct address_space *mapping,
 
 		WARN_ON_ONCE(!folio_test_locked(folio));
 
+		VM_BUG_ON_FOLIO(folio_order(folio) < min_order, folio);
 		folio->mapping = NULL;
 		/* Leave folio->index set: truncation lookup relies on it */
 
@@ -846,6 +850,7 @@ noinline int __filemap_add_folio(struct address_space *mapping,
 	int huge = folio_test_hugetlb(folio);
 	bool charged = false;
 	long nr = 1;
+	unsigned int min_order = mapping_min_folio_order(mapping);
 
 	VM_BUG_ON_FOLIO(!folio_test_locked(folio), folio);
 	VM_BUG_ON_FOLIO(folio_test_swapbacked(folio), folio);
@@ -896,6 +901,7 @@ noinline int __filemap_add_folio(struct address_space *mapping,
 			}
 		}
 
+		VM_BUG_ON_FOLIO(folio_order(folio) < min_order, folio);
 		xas_store(&xas, folio);
 		if (xas_error(&xas))
 			goto unlock;
@@ -1847,6 +1853,10 @@ struct folio *__filemap_get_folio(struct address_space *mapping, pgoff_t index,
 		fgf_t fgp_flags, gfp_t gfp)
 {
 	struct folio *folio;
+	unsigned int min_order = mapping_min_folio_order(mapping);
+	unsigned int min_nrpages = mapping_min_folio_nrpages(mapping);
+
+	index = round_down(index, min_nrpages);
 
 repeat:
 	folio = filemap_get_entry(mapping, index);
@@ -1886,7 +1896,7 @@ struct folio *__filemap_get_folio(struct address_space *mapping, pgoff_t index,
 		folio_wait_stable(folio);
 no_page:
 	if (!folio && (fgp_flags & FGP_CREAT)) {
-		unsigned order = FGF_GET_ORDER(fgp_flags);
+		unsigned int order = max(min_order, FGF_GET_ORDER(fgp_flags));
 		int err;
 
 		if ((fgp_flags & FGP_WRITE) && mapping_can_writeback(mapping))
@@ -1914,8 +1924,13 @@ 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;
+
+			VM_BUG_ON(index & ((1UL << order) - 1));
+
 			folio = filemap_alloc_folio(alloc_gfp, order);
 			if (!folio)
 				continue;
@@ -1929,7 +1944,7 @@ 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;
@@ -2424,7 +2439,8 @@ static int filemap_create_folio(struct file *file,
 	struct folio *folio;
 	int error;
 
-	folio = filemap_alloc_folio(mapping_gfp_mask(mapping), 0);
+	folio = filemap_alloc_folio(mapping_gfp_mask(mapping),
+				    mapping_min_folio_order(mapping));
 	if (!folio)
 		return -ENOMEM;
 
@@ -3682,7 +3698,8 @@ static struct folio *do_read_cache_folio(struct address_space *mapping,
 repeat:
 	folio = filemap_get_folio(mapping, index);
 	if (IS_ERR(folio)) {
-		folio = filemap_alloc_folio(gfp, 0);
+		folio = filemap_alloc_folio(gfp,
+					    mapping_min_folio_order(mapping));
 		if (!folio)
 			return ERR_PTR(-ENOMEM);
 		err = filemap_add_folio(mapping, folio, index, gfp);
-- 
2.43.0