[RFC PATCH v2 0/3] erofs-utils: compressed fragments feature

[Yue Hu]

In order to achieve greater compression ratio, let's introduce
compressed fragments feature which can merge tail of per-file or the
whole files into one special inode to reach the target.

And we can also set pcluster size to fragments inode for different
compression requirments.

In this patchset, we also improve the uncompressed data layout of
compressed files. Just write it from 'clusterofs' instead of 0 since it
can benefit from in-place I/O. For now, it only goes with fragments.

The main idea above is from Xiang.

Here is some test data of Linux 5.10.87 source code under Ubuntu 18.04:

linux-5.10.87 (erofs, uncompressed)                1.1G

linux-5.10.87 (erofs, lz4hc,12 4k fragments,4k)    301M
linux-5.10.87 (erofs, lz4hc,12 8k fragments,8k)    268M
linux-5.10.87 (erofs, lz4hc,12 16k fragments,16k)  242M
linux-5.10.87 (erofs, lz4hc,12 32k fragments,32k)  225M
linux-5.10.87 (erofs, lz4hc,12 64k fragments,64k)  217M

linux-5.10.87 (erofs, lz4hc,12 4k vanilla)         396M
linux-5.10.87 (erofs, lz4hc,12 8k vanilla)         376M
linux-5.10.87 (erofs, lz4hc,12 16k vanilla)        364M
linux-5.10.87 (erofs, lz4hc,12 32k vanilla)        359M
linux-5.10.87 (erofs, lz4hc,12 64k vanilla)        358M

Usage:
mkfs.erofs -zlz4hc,12 -C65536 -Efragments,65536 foo.erofs.img foo/

Changes since v1:
 - mainly optimize index space for fragment inode;
 - add merging tail with len <= pclustersize into fragments directly;
 - use a inode instead of nid to avoid multiple load fragments;
 - fix memory leak of building fragments;
 - minor change to diff special fragments with normal inode.
 - rebase to commit cb058526 with patch [1];
 - code cleanup.

Note that inode will be extended version (64 bytes) due to mtime, may
use 'force-inode-compact' option to reduce the size if mtime careless.

[1] https://lore.kernel.org/linux-erofs/20220722053610.23912-1-huyue2@coolpad.com/

Yue Hu (3):
  erofs-utils: lib: add support for fragments data decompression
  erofs-utils: lib: support on-disk offset for shifted decompression
  erofs-utils: introduce compressed fragments support

 include/erofs/compress.h   |   3 +-
 include/erofs/config.h     |   3 +-
 include/erofs/decompress.h |   3 ++
 include/erofs/fragments.h  |  25 +++++++++
 include/erofs/inode.h      |   2 +
 include/erofs/internal.h   |  14 +++++
 include/erofs_fs.h         |  24 ++++++---
 lib/Makefile.am            |   4 +-
 lib/compress.c             | 108 +++++++++++++++++++++++++++----------
 lib/data.c                 |  58 ++++++++++++++++++--
 lib/decompress.c           |  10 +++-
 lib/fragments.c            |  76 ++++++++++++++++++++++++++
 lib/inode.c                |  43 ++++++++++-----
 lib/super.c                |  24 ++++++++-
 lib/zmap.c                 |  18 +++++--
 mkfs/main.c                |  64 +++++++++++++++++++---
 16 files changed, 412 insertions(+), 67 deletions(-)
 create mode 100644 include/erofs/fragments.h
 create mode 100644 lib/fragments.c

-- 
2.17.1