docs: filesystems: f2fs: fix description about compress ioctl

Since commit c6140415 ("f2fs: introduce FI_COMPRESS_RELEASED
instead of using IMMUTABLE bit"), we no longer use the IMMUTABLE
bit to prevent writing data for compression. Let's correct the
corresponding documentation.

BTW, this patch fixes some alignment issues in the compress
metadata layout.
Signed-off-by: Chao Liu <liuchao@coolpad.com>
Link: https://lore.kernel.org/r/20220613020800.3379482-1-chaoliu719@gmail.comSigned-off-by: Jonathan Corbet <corbet@lwn.net>

Documentation/filesystems/f2fs.rst

@@ -818,10 +818,11 @@ Compression implementation
   Instead, the main goal is to reduce data writes to flash disk as much as
   possible, resulting in extending disk life time as well as relaxing IO
   congestion. Alternatively, we've added ioctl(F2FS_IOC_RELEASE_COMPRESS_BLOCKS)
-  interface to reclaim compressed space and show it to user after putting the
-  immutable bit. Immutable bit, after release, it doesn't allow writing/mmaping
-  on the file, until reserving compressed space via
-  ioctl(F2FS_IOC_RESERVE_COMPRESS_BLOCKS) or truncating filesize to zero.
+  interface to reclaim compressed space and show it to user after setting a
+  special flag to the inode. Once the compressed space is released, the flag
+  will block writing data to the file until either the compressed space is
+  reserved via ioctl(F2FS_IOC_RESERVE_COMPRESS_BLOCKS) or the file size is
+  truncated to zero.
 
 Compress metadata layout::
 
@@ -830,12 +831,12 @@ Compress metadata layout::
 		| cluster 1 | cluster 2 | ......... | cluster N |
 		+-----------------------------------------------+
 		.           .                       .           .
-	.                       .                .                      .
+	  .                      .                .                      .
     .         Compressed Cluster       .        .        Normal Cluster            .
     +----------+---------+---------+---------+  +---------+---------+---------+---------+
     |compr flag| block 1 | block 2 | block 3 |  | block 1 | block 2 | block 3 | block 4 |
     +----------+---------+---------+---------+  +---------+---------+---------+---------+
-	    .                             .
+	       .                             .
 	    .                                           .
 	.                                                           .
 	+-------------+-------------+----------+----------------------------+