[PATCH v3 0/2] erofs: support metadata compression

[Gao Xiang <hsiangkao@linux.alibaba.com>]

Hi,

This patchset implements metadata compression since many users are
interested in smaller image sizes (even at the cost of some I/O
latency).

In short, it uses a special "metabox" inode to gather all inode
metadata and then compresses it.  Since EROFS supports multiple
algorithms, you can select a faster algorithm (e.g., LZ4) from
the one used for data compression (e.g., LZMA).

Also see the detailed commit messages for more details.

Here are some preliminary numbers:

Command line: -zlzma,6 -Efragments,ztailpacking -C1048576

  ______________________________________________________________
 |         |_______ Vanilla _______|___ 2554769408 (2437MiB) ___|
 | Fedora  |_______ `-m4096` ______|___ 2524504064 (2408MiB) ___|
 |_________|_ `-m4096` (lz4hc,12) _|___ 2527326208 (2411MiB) ___|
 |         |_______ Vanilla _______|___  378634240 ( 362MiB) ___|
 |  AOSP   |_______ `-m4096` ______|___  377856000 ( 361MiB) ___|
 |_________|_ `-m4096` (lz4hc,12) _|___  377942016 ( 361MiB) ___|

Thanks,
Gao Xiang

v2: https://lore.kernel.org/r/20250711094004.2488-1-liubo03@inspur.com
Changes since v2:
 - refine the ondisk format and implementation.

Bo Liu (1):
  erofs: implement metadata compression

Gao Xiang (1):
  erofs: add on-disk definition for metadata compression

 fs/erofs/data.c         | 59 +++++++++++++++++++++++++----------------
 fs/erofs/decompressor.c |  2 +-
 fs/erofs/erofs_fs.h     | 15 ++++++++---
 fs/erofs/fileio.c       |  2 +-
 fs/erofs/inode.c        |  5 ++--
 fs/erofs/internal.h     | 19 ++++++++++---
 fs/erofs/super.c        | 22 +++++++++++++--
 fs/erofs/xattr.c        | 20 +++++++++-----
 fs/erofs/zdata.c        |  5 +++-
 fs/erofs/zmap.c         | 16 ++++++-----
 10 files changed, 115 insertions(+), 50 deletions(-)

-- 
2.43.5