linux-kernel - Re: [PATCH v2 2/2] x86: Add support for ZSTD-compressed kernel

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Date:   Tue, 17 Oct 2017 12:45:45 -0700
From:   Andi Kleen <ak@...ux.intel.com>
To:     Nick Terrell <terrelln@...com>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>, <linux-kernel@...r.kernel.org>,
        <x86@...nel.org>, <kernel-team@...com>, Chris Mason <clm@...com>,
        Yann Collet <cyan@...com>, Rene Rebe <rene@...ctcode.com>,
        Adam Borowski <kilobyte@...band.pl>
Subject: Re: [PATCH v2 2/2] x86: Add support for ZSTD-compressed kernel

Nick Terrell <terrelln@...com> writes:

> @@ -133,6 +133,8 @@ $(obj)/vmlinux.bin.lzo: $(vmlinux.bin.all-y) FORCE
>  	$(call if_changed,lzo)
>  $(obj)/vmlinux.bin.lz4: $(vmlinux.bin.all-y) FORCE
>  	$(call if_changed,lz4)
> +$(obj)/vmlinux.bin.zst: $(vmlinux.bin.all-y) FORCE
> +	$(call if_changed,zstd)

In my experience the biggest problem with these options is that the
special command line tools needed for the build are often not installed
on the build systems.

So we turn it off and go back to GZIP to make the kernel build again.
Or we settle on some other option, but then when a better compressor
like ZSTD comes up it's too much trouble to change all the .configs.

There were recently some patches to add a stackprotector automatic
selection that probes if gcc supports stack overflow support,
and if not falls back automatically.

A similar thing for good compression options would seem better:
have a AUTO config option that uses ZSTD and fall back to GZIP
if it's not available. Then put it into defconfig.

I suspect that would increase your user base quite a bit.

-Andi