[RFC PATCH v3 0/3] erofs-utils: compressed fragments feature

[Yue Hu]

Hi Xiang,

On Wed, 3 Aug 2022 14:07:24 +0800
Gao Xiang <hsiangkao at linux.alibaba.com> wrote:

> Hi Yue,
> 
> On Wed, Aug 03, 2022 at 11:51:27AM +0800, Yue Hu wrote:
> > 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.  
> 
> Thanks for your hard work! I will take a deep try this weekend,

Got it.

> 
> Also I'd like to enable logical cluster size != 4k for big pcluster with
> large pclustersize in order to reduce the size of compression indexes.

Let me think about this first.

Thanks.

> 
> In such cases, I think compact indexes are unnecessary.  I think it's
> already supported on the kernel side, so we just need to implement the
> userspace side.
> 
> Thanks,
> Gao 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 v2:
> >  - mainly reimplment the decompression logic for fragment inode due to
> >    kernel side;
> >  - fix compatibility issue to old image with ztailpacking feature;
> >  - move code of super.c in patch 3/3 to patch 1/3;
> >  - minor naming change.
> > 
> > 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   |   9 ++++
> >  include/erofs_fs.h         |  27 +++++++---
> >  lib/Makefile.am            |   4 +-
> >  lib/compress.c             | 108 +++++++++++++++++++++++++++----------
> >  lib/data.c                 |  28 +++++++++-
> >  lib/decompress.c           |  10 +++-
> >  lib/fragments.c            |  76 ++++++++++++++++++++++++++
> >  lib/inode.c                |  43 ++++++++++-----
> >  lib/super.c                |  24 ++++++++-
> >  lib/zmap.c                 |  26 +++++++++
> >  mkfs/main.c                |  64 +++++++++++++++++++---
> >  16 files changed, 393 insertions(+), 62 deletions(-)
> >  create mode 100644 include/erofs/fragments.h
> >  create mode 100644 lib/fragments.c
> > 
> > -- 
> > 2.17.1