On Fri, Aug 17, 2018 at 12:22:44PM -0700, Andi Kleen wrote:
> On Fri, Aug 17, 2018 at 07:57:46PM +0200, Adam Borowski wrote:
> > > The "favourite compressor" seems to roughly change every year, so if
> > > we keep adding new ones things will get more and more convoluted.
> >
> > The above patchset drops just bzip2. It is the only one that's strictly
> > beaten in every way (ratio, time, memory usage), there are also no other
>
> Does time include build time? I've been reverting back to gzip recently
> because I care very much about that.
Too lazy to benchmark a kernel image (IIRC Nick Terrell posted that a while
ago), here's copypasta of a random 16824672 byte executable, in userspace,
with default level setting:
comp decomp size
xz 8.038s 0.356s 4320292
bz2 2.265s 0.730s 5234516
zst 0.274s 0.102s 5657626
gz 0.880s 0.152s 6515505
Z 0.499s 0.133s 8932459
lzo 0.100s 0.095s 9198874
As you can see, zstd's compression time is drastically better than gzip,
while ratio is better. The default level is very low (-3 on -1..-22 scale)
but you can crank it up for stronger compression.
The defaults fit your use case.
> > uses of bzip2 anywhere in the kernel so we'd get to drop its code
> > completely: 900 lines of Linus' happiness.
>
> Great!
>
> > Other candidates are lzo and bare lzma (you want lz4, zstd or xz instead),
> > but those are used elsewhere thus there's hardly any gain. If you want them
> > gone, please say so -- I'll include their droppage.
>
> Yes would be good to remove the kernel image support for those too
> just to simplify the config process, even if it doesn't save much code.
There's one caveat: fast choices are quite new:
* lz4 userspace tools are not even in current Debian stable (just unstable)
* uncompressed kernel got in only this merge window
* zstd has userspace tools in Debian stable but is not merged into the
kernel yet
(other dists are probably similar)
Thus, it might be a good idea to keep lzo for a while longer.
Bare lzma can probably go -- xz filters are nice for binaries of archs it
knows (disabled otherwise), and lack of header requires hacks to find out
the payload's size.
So it's up to you guys: do you want me to drop lzo and/or lzma?
We can also drop them just for vmlinuz but not initrd.
Meow!
--
⢀⣴⠾⠻⢶⣦⠀ What Would Jesus Do, MUD/MMORPG edition:
⣾⠁⢰⠒⠀⣿⡁ • multiplay with an admin char to benefit your mortal [Mt3:16-17]
⢿⡄⠘⠷⠚⠋⠀ • abuse item cloning bugs [Mt14:17-20, Mt15:34-37]
⠈⠳⣄⠀⠀⠀⠀ • use glitches to walk on water [Mt14:25-26]
