Date:   Wed, 7 Apr 2021 22:53:59 +0900
From:   Masahiro Yamada <masahiroy@...nel.org>
To:     Nick Terrell <terrelln@...com>
Cc:     Oleksandr Natalenko <oleksandr@...alenko.name>,
        Piotr Gorski <lucjan.lucjanov@...il.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Linux Kbuild mailing list <linux-kbuild@...r.kernel.org>,
        Michal Marek <michal.lkml@...kovi.net>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Kees Cook <keescook@...omium.org>,
        Nathan Chancellor <nathan@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Valentin Schneider <valentin.schneider@....com>,
        "Jan Alexander Steffens (heftig)" <jan.steffens@...il.com>,
        David Howells <dhowells@...hat.com>,
        Johannes Weiner <hannes@...xchg.org>
Subject: Re: [PATCH] init: add support for zstd compressed modules

On Thu, Apr 1, 2021 at 4:21 AM Nick Terrell <terrelln@...com> wrote:
>
>
>
> > On Mar 31, 2021, at 10:48 AM, Oleksandr Natalenko <oleksandr@...alenko.name> wrote:
> >
> > Hello.
> >
> > On Wed, Mar 31, 2021 at 05:39:25PM +0000, Nick Terrell wrote:
> >>
> >>
> >>> On Mar 30, 2021, at 4:50 AM, Oleksandr Natalenko <oleksandr@...alenko.name> wrote:
> >>>
> >>> On Tue, Mar 30, 2021 at 01:32:35PM +0200, Piotr Gorski wrote:
> >>>> kmod 28 supports modules compressed in zstd format so let's add this possibility to kernel.
> >>>>
> >>>> Signed-off-by: Piotr Gorski <lucjan.lucjanov@...il.com>
> >>>> ---
> >>>> Makefile     | 7 +++++--
> >>>> init/Kconfig | 9 ++++++---
> >>>> 2 files changed, 11 insertions(+), 5 deletions(-)
> >>>>
> >>>> diff --git a/Makefile b/Makefile
> >>>> index 5160ff8903c1..82f4f4cc2955 100644
> >>>> --- a/Makefile
> >>>> +++ b/Makefile
> >>>> @@ -1156,8 +1156,8 @@ endif # INSTALL_MOD_STRIP
> >>>> export mod_strip_cmd
> >>>>
> >>>> # CONFIG_MODULE_COMPRESS, if defined, will cause module to be compressed
> >>>> -# after they are installed in agreement with CONFIG_MODULE_COMPRESS_GZIP
> >>>> -# or CONFIG_MODULE_COMPRESS_XZ.
> >>>> +# after they are installed in agreement with CONFIG_MODULE_COMPRESS_GZIP,
> >>>> +# CONFIG_MODULE_COMPRESS_XZ, or CONFIG_MODULE_COMPRESS_ZSTD.
> >>>>
> >>>> mod_compress_cmd = true
> >>>> ifdef CONFIG_MODULE_COMPRESS
> >>>> @@ -1167,6 +1167,9 @@ ifdef CONFIG_MODULE_COMPRESS
> >>>>  ifdef CONFIG_MODULE_COMPRESS_XZ
> >>>>    mod_compress_cmd = $(XZ) --lzma2=dict=2MiB -f
> >>>>  endif # CONFIG_MODULE_COMPRESS_XZ
> >>>> +  ifdef CONFIG_MODULE_COMPRESS_ZSTD
> >>>> +    mod_compress_cmd = $(ZSTD) -T0 --rm -f -q
> >>
> >> This will use the default zstd level, level 3. I think it would make more sense to use a high
> >> compression level. Level 19 would probably be a good choice. That will choose a window
> >> size of up to 8MB, meaning the decompressor needs to allocate that much memory. If that
> >> is unacceptable, you could use `zstd -T0 --rm -f -q -19 --zstd=wlog=21`, which will use a
> >> window size of up to 2MB, to match the XZ command. Note that if the file is smaller than
> >> the window size, it will be shrunk to the smallest power of two at least as large as the file.
> >
> > Please no. We've already done that with initramfs in Arch, and it
> > increased the time to generate it enormously.
> >
> > I understand that building a kernel is a more rare operation than
> > regenerating initramfs, but still I'd go against hard-coding the level.
> > And if it should be specified anyway, I'd opt in for an explicit
> > configuration option. Remember, not all the kernel are built on
> > build farms...
> >
> > FWIW, Piotr originally used level 9 which worked okay, but I insisted
> > on sending the patch initially without specifying level at all like it is
> > done for other compressors. If this is a wrong approach, then oh meh,
> > mea culpa ;).
> >
> > Whatever default non-standard compression level you choose, I'm fine
> > as long as I can change it without editing Makefile.
>
> That makes sense to me. I have a deep seated need to compress files as
> efficiently as possible for widely distributed packages. But, I understand that
> slow compression significantly impacts build times for quick iteration. I’d be
> happy with a compression level parameter that defaults to a happy middle.
>
> I’m also fine with taking this patch as-is if it is easier, and I can put up another
> patch that adds a compression level parameter, since I don’t want to block
> merging this.


I do not want to take such a patch.
Meeking everyone's requirement
results in a bad project for everyone.


Does this work for you?

make modules_install ZSTD="zstd -19"












> Best,
> Nick Terrell
>
> > Thanks!
> >
> >>
> >> Best,
> >> Nick Terrell
> >>
> >>>> +  endif # CONFIG_MODULE_COMPRESS_ZSTD
> >>>> endif # CONFIG_MODULE_COMPRESS
> >>>> export mod_compress_cmd
> >>>>
> >>>> diff --git a/init/Kconfig b/init/Kconfig
> >>>> index 8c2cfd88f6ef..86a452bc2747 100644
> >>>> --- a/init/Kconfig
> >>>> +++ b/init/Kconfig
> >>>> @@ -2250,8 +2250,8 @@ config MODULE_COMPRESS
> >>>>    bool "Compress modules on installation"
> >>>>    help
> >>>>
> >>>> -    Compresses kernel modules when 'make modules_install' is run; gzip or
> >>>> -    xz depending on "Compression algorithm" below.
> >>>> +    Compresses kernel modules when 'make modules_install' is run; gzip,
> >>>> +    xz, or zstd depending on "Compression algorithm" below.
> >>>>
> >>>>      module-init-tools MAY support gzip, and kmod MAY support gzip and xz.
> >>>>
> >>>> @@ -2273,7 +2273,7 @@ choice
> >>>>      This determines which sort of compression will be used during
> >>>>      'make modules_install'.
> >>>>
> >>>> -    GZIP (default) and XZ are supported.
> >>>> +    GZIP (default), XZ, and ZSTD are supported.
> >>>>
> >>>> config MODULE_COMPRESS_GZIP
> >>>>    bool "GZIP"
> >>>> @@ -2281,6 +2281,9 @@ config MODULE_COMPRESS_GZIP
> >>>> config MODULE_COMPRESS_XZ
> >>>>    bool "XZ"
> >>>>
> >>>> +config MODULE_COMPRESS_ZSTD
> >>>> +  bool "ZSTD"
> >>>> +
> >>>> endchoice
> >>>>
> >>>> config MODULE_ALLOW_MISSING_NAMESPACE_IMPORTS
> >>>> --
> >>>> 2.31.0.97.g1424303384
> >>>>
> >>>
> >>> Great!
> >>>
> >>> Reviewed-by: Oleksandr Natalenko <oleksandr@...alenko.name>
> >>>
> >>> This works perfectly fine in Arch Linux if accompanied by the
> >>> following mkinitcpio amendment: [1].
> >>>
> >>> I'm also Cc'ing other people from get_maintainers output just
> >>> to make this submission more visible.
> >>>
> >>> Thanks.
> >>>
> >>> [1] https://github.com/archlinux/mkinitcpio/pull/43
> >>>
> >>> --
> >>> Oleksandr Natalenko (post-factum)
> >>
> >
> > --
> >  Oleksandr Natalenko (post-factum)
>


-- 
Best Regards
Masahiro Yamada

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