linux-kernel - Re: [PATCH] initramfs: restore default compression behaviour

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Date:   Mon, 16 Mar 2020 11:22:03 +0000
From:   Eugeniy Paltsev <Eugeniy.Paltsev@...opsys.com>
To:     Masahiro Yamada <masahiroy@...nel.org>
CC:     Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        arcml <linux-snps-arc@...ts.infradead.org>,
        Vineet Gupta <Vineet.Gupta1@...opsys.com>,
        Alexey Brodkin <Alexey.Brodkin@...opsys.com>
Subject: Re: [PATCH] initramfs: restore default compression behaviour

Hi Masahiro,

>From: Masahiro Yamada <masahiroy@...nel.org>
>Sent: Wednesday, March 11, 2020 23:12
>To: Eugeniy Paltsev
>Cc: Linux Kernel Mailing List; arcml; Vineet Gupta; Alexey Brodkin
>Subject: Re: [PATCH] initramfs: restore default compression behaviour
>
>Hi Eugeniy.
>
>On Wed, Mar 11, 2020 at 7:22 PM Eugeniy Paltsev
><Eugeniy.Paltsev@...opsys.com> wrote:
>>
>> Even though INITRAMFS_SOURCE kconfig option isn't set in most of
>> defconfigs it is used (set) extensively by various build systems.
>> Commit f26661e12765 ("initramfs: make initramfs compression choice
>> non-optional") has changed default compression mode. Previously we
>> compress initramfs using available compression algorithm. Now
>> we don't use any compression at all by default.
>> It significantly increases the image size in case of build system
>> chooses embedded initramfs. Initially I faced with this issue while
>> using buildroot.
>>
>> As of today it's not possible to set preferred compression mode
>> in target defconfig as this option depends on INITRAMFS_SOURCE
>> being set.
>> Modification of build systems doesn't look like good option in this
>> case as it requires to check against kernel version when setting
>> compression mode. The reason for this is that kconfig options
>> describing compression mode was renamed (in same patch series)
>
>Which commit?
>
>I do not remember the renaming of kconfig options
>with this regard.

Ok, I've checked it again - looks like I was confused a bit by
"CONFIG_INITRAMFS_COMPRESSION" option
as in v5.5 kernel I have in ".config":
CONFIG_INITRAMFS_COMPRESSION=".gz"

And for v5.6-rc1 I have in ".config":
CONFIG_INITRAMFS_COMPRESSION_GZIP=y

But they are different options actually...

>
>> so
>> we are not able to simply enable one option for old and new kernels.
>>
>> Given that I propose to use GZIP as default here instead of NO
>> compression. It should be used only when available but given that
>> gzip is enabled by default it looks like good enough choice.
>
>
>Another solution would be to move
>INITRAMFS_COMPRESSION_NONE to the end of the choice menu.
>
>The default of the choice menu is the first visible entry.
>
>GZIP if RD_GZIP is defined, BZIP2 if RD_BZIP2 is defined ...

Thanks for advice. It looks like an excellent option here, I'll send a patch.

>
>> Signed-off-by: Eugeniy Paltsev <Eugeniy.Paltsev@...opsys.com>
>> ---
>>  usr/Kconfig | 1 +
>>  1 file changed, 1 insertion(+)
>>
>> diff --git a/usr/Kconfig b/usr/Kconfig
>> index bdf5bbd40727..690ef9020819 100644
>> --- a/usr/Kconfig
>> +++ b/usr/Kconfig
>> @@ -102,6 +102,7 @@ config RD_LZ4
>>
>>  choice
>>         prompt "Built-in initramfs compression mode"
>> +       default INITRAMFS_COMPRESSION_GZIP if RD_GZIP
>>         depends on INITRAMFS_SOURCE != ""
>>         help
>>           This option allows you to decide by which algorithm the builtin
>> --
>> 2.21.1
>>
>--
>Best Regards
>Masahiro Yamada