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>

1 files changed, 39 insertions, 0 deletions

diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index 998ddce49093..3d03a6eb0ea0 100644
--- a/fs/ext4/super.c
+++ b/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;