RE: [PATCH v14 06/10] fs/ntfs3: Add compression

[Konstantin Komarov <almaz.alexandrovich@paragon-software.com>]

From: Eric Biggers <ebiggers@kernel.org>
Sent: Friday, December 4, 2020 9:39 PM
> To: Konstantin Komarov <almaz.alexandrovich@paragon-software.com>
> Cc: linux-fsdevel@vger.kernel.org; viro@zeniv.linux.org.uk; linux-kernel@vger.kernel.org; pali@kernel.org; dsterba@suse.cz;
> aaptel@suse.com; willy@infradead.org; rdunlap@infradead.org; joe@perches.com; mark@harmstone.com; nborisov@suse.com;
> linux-ntfs-dev@lists.sourceforge.net; anton@tuxera.com; dan.carpenter@oracle.com; hch@lst.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@paragon-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).
> 

Hi Eric! Fixed in V15!

> 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".
> 

Thanks, fixed as well.

> 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

We used the newest code initially. Looking at the commit you've pointed out, but it will
take some time as needs to pass full set of tests with new code. On the differences you've
mentioned between the first and latest code in ntfs-3g system compression: we've removed
the optimizations (needed to go into kernel), also the reparse points stuff is being parsed by
ntfs3 driver itself. Given this, doesn't seems there are many differences remain.
Also, we'll follow your recommendations, if you highly recommend to stick to the commit
you've mentioned (but at this moment it seems "newer=better" formula still valid).

Thanks!