Re: [PATCH] dist: add dist-zstd option

[Jim Meyering]

On Fri, Oct 4, 2019 at 8:03 AM Giuseppe Scrivano <address@hidden> wrote:
> add support for using the zstd compression algorithm.

Hi Giuseppe,
Thank you for that patch.
I've adjusted it and propose the attached, which makes these changes:
- add tests
- that exposed the need for a correction, s/-d/-dc/ in distdir.am
- extend documentation
- use the 3-byte suffix, .zst, not .zstd
- use -19 as the default compression level

We must use -19 as the default, not the aggressive --ultra -22 -- the
package maintainer can always override with ZSTD_OPT if they know all
clients will always have sufficient memory. In the early days, some
reported failure to decompress a "xz -9e"-compressed coreutils tarball
on tiny-memory routers. Like zstd's --ultra settings, xz's -9 requires
more RAM when DEcompressing -- so automake defaults to xz's "-e" (use
extra CPU only) and used -e8 for coreutils
(https://git.sv.gnu.org/cgit/coreutils.git/commit/?id=v8.15-61-gc1d07237a):
i.e., still require 32MiB more RAM, but not the 64MiB that "-9" would
require.

Cc'd the zstd author, Yann Collet, in case he'd like to add something.

Giuseppe, please re-review this diff and its updated commit log.

automake-zstd.diff
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