ext4: use non-movable memory for the ext4 superblock

Since the ext4 superblock is not released until the file system is
unmounted, allocate the buffer cache entry for the ext4 superblock out
of the non-moveable are to allow page migrations and thus CMA
allocations to more easily succeed if the CMA area is limited.
Signed-off-by: Gioh Kim <gioh.kim@lge.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Reviewed-by: Jan Kara <jack@suse.cz>

fs/ext4/super.c

@@ -3436,7 +3436,7 @@ static int ext4_fill_super(struct super_block *sb, void *data, int silent)
 		logical_sb_block = sb_block;
 	}
 
-	if (!(bh = sb_bread(sb, logical_sb_block))) {
+	if (!(bh = sb_bread_unmovable(sb, logical_sb_block))) {
 		ext4_msg(sb, KERN_ERR, "unable to read superblock");
 		goto out_fail;
 	}
@@ -3646,7 +3646,7 @@ static int ext4_fill_super(struct super_block *sb, void *data, int silent)
 		brelse(bh);
 		logical_sb_block = sb_block * EXT4_MIN_BLOCK_SIZE;
 		offset = do_div(logical_sb_block, blocksize);
-		bh = sb_bread(sb, logical_sb_block);
+		bh = sb_bread_unmovable(sb, logical_sb_block);
 		if (!bh) {
 			ext4_msg(sb, KERN_ERR,
 			       "Can't read superblock on 2nd try");
@@ -3868,7 +3868,7 @@ static int ext4_fill_super(struct super_block *sb, void *data, int silent)
 
 	for (i = 0; i < db_count; i++) {
 		block = descriptor_loc(sb, logical_sb_block, i);
-		sbi->s_group_desc[i] = sb_bread(sb, block);
+		sbi->s_group_desc[i] = sb_bread_unmovable(sb, block);
 		if (!sbi->s_group_desc[i]) {
 			ext4_msg(sb, KERN_ERR,
 			       "can't read group descriptor %d", i);