[OE-core] [PATCH] Set XZ_COMPRESSION_LEVEL to -9
Adrian Bunk
bunk at stusta.de
Sat Apr 13 06:17:34 UTC 2019
On Fri, Apr 12, 2019 at 02:44:05PM -0700, Andre McCurdy wrote:
> On Fri, Apr 12, 2019 at 2:09 PM Adrian Bunk <bunk at stusta.de> wrote:
> >
> > It is consistent with other compressors also using their
> > best compression.
> >
> > xz is currently the option that offers best compression,
> > using settings even lower than the default is surprising
> > and makes it harder to choose the best available compression.
> >
> > For anyone who cares about compression time using a different
> > option like gzip or bzip2 is the logical choice.
>
> The concern with xz's highest compression level is memory usage rather
> than CPU time. Quoting from the manpage:
>
> Preset DictSize CompCPU CompMem DecMem
> -0 256 KiB 0 3 MiB 1 MiB
> -1 1 MiB 1 9 MiB 2 MiB
> -2 2 MiB 2 17 MiB 3 MiB
> -3 4 MiB 3 32 MiB 5 MiB
> -4 4 MiB 4 48 MiB 5 MiB
> -5 8 MiB 5 94 MiB 9 MiB
> -6 8 MiB 6 94 MiB 9 MiB
> -7 16 MiB 6 186 MiB 17 MiB
> -8 32 MiB 6 370 MiB 33 MiB
> -9 64 MiB 6 674 MiB 65 MiB
>
> Given that these are per-thread the memory requirements may start to
> get a little unreasonable with xz -9. We do limit usage to 50% of
> physical memory via XZ_DEFAULTS though so maybe it's not a big
> concern?
Due to the limit, and also due to the fact that build machines with
very low RAM/core are likely to have bigger problems earlier:
The compile task of a recipe spawns the same number of gcc processes,
and there can be several compile tasks running.
gcc memory usage when compiling C++ code like webkit can be worse than
these per-thread numbers.
> Either way, perhaps now would be a good time to remove
> XZ_COMPRESSION_LEVEL from image_types.bbclass and instead just include
> the compression level option in XZ_DEFAULTS so that it gets used
> consistently everywhere.
OPKGBUILDCMD uses XZ_DEFAULTS, and the decompression memory requirement
on the target for -9 might be a problem if someone uses package feeds
on low-memory targets.
cu
Adrian
--
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of the darkness. There had been need of rain for many days.
"Only a promise," Lao Er said.
Pearl S. Buck - Dragon Seed
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