f2fs: remove unneeded in-memory i_crtime copy

i_crtime will never change after inode creation, so we don't need
to copy it into f2fs_inode_info.i_disk_time[3], and monitor its
change to decide whether updating inode page, remove related stuff.
Signed-off-by: Chao Yu <chao@kernel.org>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>

fs/f2fs/f2fs.h

@@ -843,7 +843,7 @@ struct f2fs_inode_info {
 	kprojid_t i_projid;		/* id for project quota */
 	int i_inline_xattr_size;	/* inline xattr size */
 	struct timespec64 i_crtime;	/* inode creation time */
-	struct timespec64 i_disk_time[4];/* inode disk times */
+	struct timespec64 i_disk_time[3];/* inode disk times */
 
 	/* for file compress */
 	atomic_t i_compr_blocks;		/* # of compressed blocks */
@@ -3292,9 +3292,6 @@ static inline bool f2fs_is_time_consistent(struct inode *inode)
 		return false;
 	if (!timespec64_equal(F2FS_I(inode)->i_disk_time + 2, &inode->i_mtime))
 		return false;
-	if (!timespec64_equal(F2FS_I(inode)->i_disk_time + 3,
-						&F2FS_I(inode)->i_crtime))
-		return false;
 	return true;
 }
 

fs/f2fs/inode.c

@@ -326,7 +326,6 @@ static void init_idisk_time(struct inode *inode)
 	fi->i_disk_time[0] = inode->i_atime;
 	fi->i_disk_time[1] = inode->i_ctime;
 	fi->i_disk_time[2] = inode->i_mtime;
-	fi->i_disk_time[3] = fi->i_crtime;
 }
 
 static int do_read_inode(struct inode *inode)