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Bug#940887: Integrate ZSTD patches *Kernel compression: add ZSTD, remove LZMA1 and BZIP2*

Cross-posted to 2 groups.

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Package: src:linux
Version: 5.2.9-2
Severity: wishlist


Dear Linux folks,


It’d be awesome, if you applied Adam’s and Nick’s patches for ZSTD 
support [1] to the Debian kernel, so users can test those early for the 
next Debian release.

Here is the cover letter text:

> Hi!
> As new compressors get invented, they tend to find their way into the
> kernel, yet we never prune superseded ones.  It's time to do so.
> 
> In particular, BZIP2 is drastically slower than other compressors we
> have, even when they achieve smaller sizes.  It takes more memory, too.
> And, BZIP2 is not used anywhere else in the kernel -- just for booting
> the kernel itself and the initrd.  Thus, we can drop it from the tree
> completely, making Linus happier by around 900 lines.
> 
> LZMA1 is redundant with XZ (LZMA2), and unlike the latter, it uses its own
> copy of code that's not shared with anything else (some drivers use XZ).
> Let's drop it as well.  Some bootloaders can use it thus let's keep the
> Kconfig option, but I left no piece of code inside the kernel itself.
> 
> On the other hand, Nick Terrell has a couple of patches adding ZSTD support
> (using code already in use in multiple pieces around the kernel).  ZSTD is
> strong and fast, obsoleting all mid-range compressors.  As the removal of
> BZIP2 and LZMA1 would be hopelessly entangled with this addition, I'm
> resending Nick's patches here.  I've been booting using them since Oct'17
> on amd64 (kernel+initrd), armhf and arm64 (initrd) without issues, other
> folks tested various other architectures as well.
> 
> Thus, I'd recommend people to use:
> * XZ for most machines
> * ZSTD where speed is important
> * maaaaybe LZ4 is some special cases
> (grub and u-boot are ridiculously slow at reading, making fast but weak
> decompressors a net loss.  On the other hand, XZ decompresses pretty fast
> but is very slow at compress time, making ZSTD preferred for rapid devel
> cycles.)
> 
> * we can't get rid of GZIP in foreseable future
> * LZO is obsolete but is used elsewhere in the kernel
> 
> Total:
>  69 files changed, 518 insertions(+), 1785 deletions(-)
> 
> Not sure whose tree this patchset should go through.  I'm also not sure
> how finely split into commits you want the arch bits be; I included
> defconfig bits all together, yet separated code changes per-arch.
> 
> 
> Meow!


Kind regards,

Paul


[1]: https://lore.kernel.org/patchwork/cover/1009317/

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Bug#940887: Integrate ZSTD patches *Kernel compression: add ZSTD, remove LZMA1 and BZIP2* Paul Menzel <pmenzel@molgen.mpg.de> - 2019-09-21 16:10 +0200
  Bug#940887: Integrate ZSTD patches *Kernel compression: add ZSTD, remove LZMA1 and BZIP2* Adam Borowski <kilobyte@angband.pl> - 2019-09-22 17:10 +0200

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