linux-kernel - Re: [PATCH v8 6/7] x86: Add support for ZSTD compressed kernel

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Date:   Fri, 24 Jul 2020 15:46:25 +0200
From:   Adam Borowski <kilobyte@...band.pl>
To:     Ingo Molnar <mingo@...nel.org>
Cc:     Nick Terrell <nickrterrell@...il.com>,
        Borislav Petkov <bp@...en8.de>,
        Thomas Gleixner <tglx@...utronix.de>,
        linux-kernel@...r.kernel.org, Chris Mason <clm@...com>,
        linux-kbuild@...r.kernel.org, x86@...nel.org,
        gregkh@...uxfoundation.org, Petr Malat <oss@...at.biz>,
        Kees Cook <keescook@...omium.org>,
        Kernel Team <Kernel-team@...com>,
        Patrick Williams <patrickw3@...com>, rmikey@...com,
        Patrick Williams <patrick@...cx.xyz>,
        Sedat Dilek <sedat.dilek@...il.com>,
        Norbert Lange <nolange79@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Alex Xu <alex_y_xu@...oo.ca>,
        Arvind Sankar <nivedita@...m.mit.edu>,
        Nick Terrell <terrelln@...com>
Subject: Re: [PATCH v8 6/7] x86: Add support for ZSTD compressed kernel

On Fri, Jul 24, 2020 at 02:26:40PM +0200, Ingo Molnar wrote:
> > -#ifdef CONFIG_KERNEL_BZIP2
> > +#if defined(CONFIG_KERNEL_BZIP2)
> >  # define BOOT_HEAP_SIZE		0x400000
> > -#else /* !CONFIG_KERNEL_BZIP2 */
> > +#elif defined(CONFIG_KERNEL_ZSTD)
> > +# define BOOT_HEAP_SIZE		 0x30000
> > +#else
> >  # define BOOT_HEAP_SIZE		 0x10000
> >  #endif
> 
> So the other patches explain why the decompression buffer extra space 
> was increased from 64k to 128k, but is there a similar 
> calculation/estimate for bumping BOOT_HEAD_SIZE from 64k to 192k?
> 
> Admittedly the BZ2 exception doesn't set a good example, but maybe we 
> can do this for ZSTD?

By the way, I have a patchset on top of this, to drop BZ2 and LZMA(1)
support, that should clean up this code somewhat.  And bring a lot of
lines of Linus happiness, as both bzip2 and lzma code are not used by
anything else in the kernel, unlike lzma2 (xz).

If you draw a speed-vs-size graph, at no point bzip2 or lzma are a good
choice, while zstd wins by a large margin for most of the range.


Meow!
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