linux-kernel - Re: [PATCH v14 06/10] fs/ntfs3: Add compression

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Date:   Fri, 4 Dec 2020 10:38:37 -0800
From:   Eric Biggers <ebiggers@...nel.org>
To:     Konstantin Komarov <almaz.alexandrovich@...agon-software.com>
Cc:     linux-fsdevel@...r.kernel.org, viro@...iv.linux.org.uk,
        linux-kernel@...r.kernel.org, pali@...nel.org, dsterba@...e.cz,
        aaptel@...e.com, willy@...radead.org, rdunlap@...radead.org,
        joe@...ches.com, mark@...mstone.com, nborisov@...e.com,
        linux-ntfs-dev@...ts.sourceforge.net, anton@...era.com,
        dan.carpenter@...cle.com, hch@....de
Subject: Re: [PATCH v14 06/10] fs/ntfs3: Add compression

On Fri, Dec 04, 2020 at 06:45:56PM +0300, Konstantin Komarov wrote:
> This adds compression
> 
> Signed-off-by: Konstantin Komarov <almaz.alexandrovich@...agon-software.com>
> ---
>  fs/ntfs3/lib/common_defs.h       | 196 +++++++++++
>  fs/ntfs3/lib/decompress_common.c | 314 +++++++++++++++++
>  fs/ntfs3/lib/decompress_common.h | 558 +++++++++++++++++++++++++++++++
>  fs/ntfs3/lib/lzx_common.c        | 204 +++++++++++
>  fs/ntfs3/lib/lzx_common.h        |  31 ++
>  fs/ntfs3/lib/lzx_constants.h     | 113 +++++++
>  fs/ntfs3/lib/lzx_decompress.c    | 553 ++++++++++++++++++++++++++++++
>  fs/ntfs3/lib/xpress_constants.h  |  23 ++
>  fs/ntfs3/lib/xpress_decompress.c | 165 +++++++++
>  fs/ntfs3/lznt.c                  | 452 +++++++++++++++++++++++++
>  10 files changed, 2609 insertions(+)
>  create mode 100644 fs/ntfs3/lib/common_defs.h
>  create mode 100644 fs/ntfs3/lib/decompress_common.c
>  create mode 100644 fs/ntfs3/lib/decompress_common.h
>  create mode 100644 fs/ntfs3/lib/lzx_common.c
>  create mode 100644 fs/ntfs3/lib/lzx_common.h
>  create mode 100644 fs/ntfs3/lib/lzx_constants.h
>  create mode 100644 fs/ntfs3/lib/lzx_decompress.c
>  create mode 100644 fs/ntfs3/lib/xpress_constants.h
>  create mode 100644 fs/ntfs3/lib/xpress_decompress.c
>  create mode 100644 fs/ntfs3/lznt.c

This really could use a much better commit message.  Including mentioning where
the LZX and XPRESS decompression code came from
(https://github.com/ebiggers/ntfs-3g-system-compression).

Also note you've marked the files as "SPDX-License-Identifier: GPL-2.0",
but they really are "SPDX-License-Identifier: GPL-2.0-or-later".

Also I still think you should consider using the simpler version from
ntfs-3g-system-compression commit 3ddd227ee8e3, which I had originally intended
to be included in NTFS-3G itself.  That version was fewer lines of code and
fewer files, as it was simplified for decompression-only.  The latest version
(the one you're using) is shared with a project that also implements compression
(so that I can more easily maintain both projects), so it's more complex than
needed for decompression-only support.  But in the kernel context it may make
sense to go with a simpler version.  There are a few performance optimizations
you'd miss by going with the older version, but they weren't too significant,
and probably you don't need to squeeze out every bit of performance possible
when reading XPRESS and LZX-compressed files in this context?

- Eric