ext4: add checks for large folio incompatibilities when BS > PS

Supporting a block size greater than the page size (BS > PS) requires
support for large folios. However, several features (e.g., encrypt)
do not yet support large folios.

To prevent conflicts, this patch adds checks at mount time to prohibit
these features from being used when BS > PS. Since these features cannot
be changed on remount, there is no need to check on remount.

This patch adds s_max_folio_order, initialized during mount according to
filesystem features and mount options. If s_max_folio_order is 0, large
folios are disabled.

With this in place, ext4_set_inode_mapping_order() can be simplified by
checking s_max_folio_order, avoiding redundant checks.

Signed-off-by: Baokun Li <libaokun1@huawei.com>
Reviewed-by: Jan Kara <jack@suse.cz>
Reviewed-by: Zhang Yi <yi.zhang@huawei.com>
Reviewed-by: Ojaswin Mujoo <ojaswin@linux.ibm.com>
Message-ID: <20251121090654.631996-24-libaokun@huaweicloud.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>

Author: LiBaokun96

fs/ext4/ext4.h

@@ -1705,7 +1705,9 @@ struct ext4_sb_info {
 	unsigned long s_last_trim_minblks;
 
 	/* minimum folio order of a page cache allocation */
-	unsigned int s_min_folio_order;
+	u16 s_min_folio_order;
+	/* supported maximum folio order, 0 means not supported */
+	u16 s_max_folio_order;
 
 	/* Precomputed FS UUID checksum for seeding other checksums */
 	__u32 s_csum_seed;

fs/ext4/inode.c

@@ -5148,41 +5148,23 @@ static int check_igot_inode(struct inode *inode, ext4_iget_flags flags,
 	return -EFSCORRUPTED;
 }
 
-static bool ext4_should_enable_large_folio(struct inode *inode)
+void ext4_set_inode_mapping_order(struct inode *inode)
 {
 	struct super_block *sb = inode->i_sb;
+	u16 min_order, max_order;
 
-	if (!S_ISREG(inode->i_mode))
-		return false;
-	if (ext4_has_feature_encrypt(sb))
-		return false;
-
-	return true;
-}
-
-/*
- * Limit the maximum folio order to 2048 blocks to prevent overestimation
- * of reserve handle credits during the folio writeback in environments
- * where the PAGE_SIZE exceeds 4KB.
- */
-#define EXT4_MAX_PAGECACHE_ORDER(i)		\
-		umin(MAX_PAGECACHE_ORDER, (11 + (i)->i_blkbits - PAGE_SHIFT))
-void ext4_set_inode_mapping_order(struct inode *inode)
-{
-	u32 max_order;
+	max_order = EXT4_SB(sb)->s_max_folio_order;
+	if (!max_order)
+		return;
 
-	if (!ext4_should_enable_large_folio(inode))
+	min_order = EXT4_SB(sb)->s_min_folio_order;
+	if (!min_order && !S_ISREG(inode->i_mode))
 		return;
 
-	if (test_opt(inode->i_sb, DATA_FLAGS) == EXT4_MOUNT_JOURNAL_DATA ||
-	    ext4_test_inode_flag(inode, EXT4_INODE_JOURNAL_DATA))
-		max_order = EXT4_SB(inode->i_sb)->s_min_folio_order;
-	else
-		max_order = EXT4_MAX_PAGECACHE_ORDER(inode);
+	if (ext4_test_inode_flag(inode, EXT4_INODE_JOURNAL_DATA))
+		max_order = min_order;
 
-	mapping_set_folio_order_range(inode->i_mapping,
-				      EXT4_SB(inode->i_sb)->s_min_folio_order,
-				      max_order);
+	mapping_set_folio_order_range(inode->i_mapping, min_order, max_order);
 }
 
 struct inode *__ext4_iget(struct super_block *sb, unsigned long ino,

fs/ext4/super.c

@@ -5042,6 +5042,41 @@ static const char *ext4_has_journal_option(struct super_block *sb)
 	return NULL;
 }
 
+/*
+ * Limit the maximum folio order to 2048 blocks to prevent overestimation
+ * of reserve handle credits during the folio writeback in environments
+ * where the PAGE_SIZE exceeds 4KB.
+ */
+#define EXT4_MAX_PAGECACHE_ORDER(sb)		\
+		umin(MAX_PAGECACHE_ORDER, (11 + (sb)->s_blocksize_bits - PAGE_SHIFT))
+static void ext4_set_max_mapping_order(struct super_block *sb)
+{
+	struct ext4_sb_info *sbi = EXT4_SB(sb);
+
+	if (test_opt(sb, DATA_FLAGS) == EXT4_MOUNT_JOURNAL_DATA)
+		sbi->s_max_folio_order = sbi->s_min_folio_order;
+	else
+		sbi->s_max_folio_order = EXT4_MAX_PAGECACHE_ORDER(sb);
+}
+
+static int ext4_check_large_folio(struct super_block *sb)
+{
+	const char *err_str = NULL;
+
+	if (ext4_has_feature_encrypt(sb))
+		err_str = "encrypt";
+
+	if (!err_str) {
+		ext4_set_max_mapping_order(sb);
+	} else if (sb->s_blocksize > PAGE_SIZE) {
+		ext4_msg(sb, KERN_ERR, "bs(%lu) > ps(%lu) unsupported for %s",
+			 sb->s_blocksize, PAGE_SIZE, err_str);
+		return -EINVAL;
+	}
+
+	return 0;
+}
+
 static int ext4_load_super(struct super_block *sb, ext4_fsblk_t *lsb,
 			   int silent)
 {
@@ -5318,6 +5353,10 @@ static int __ext4_fill_super(struct fs_context *fc, struct super_block *sb)
 
 	ext4_apply_options(fc, sb);
 
+	err = ext4_check_large_folio(sb);
+	if (err < 0)
+		goto failed_mount;
+
 	err = ext4_encoding_init(sb, es);
 	if (err)
 		goto failed_mount;