linux-kernel - Re: [PATCH] init: add support for zstd compressed modules

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Message-ID: <8EC13983-4A78-422B-BCA4-16A250B7B5FC@fb.com>
Date:   Wed, 7 Apr 2021 17:45:14 +0000
From:   Nick Terrell <terrelln@...com>
To:     Masahiro Yamada <masahiroy@...nel.org>
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 Apr 7, 2021, at 6:53 AM, Masahiro Yamada <masahiroy@...nel.org> wrote:
> 
> 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"

Yeah, that’s perfect. Do you think it is worth mentioning in the docs for
`MODULE_COMPRESS_ZSTD`?

Best,
Nick

>> 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