[PATCH] maint: tweak xz options to compress the release tarball even more

[Jim Meyering]

Recent discussion reminded me of this languishing patch.
The only reason to be wary is that it increases the decompression-time
memory requirement to 48MiB (from 32MiB).

At least one very-small-system user complained back when I compressed
some release tarball using -9: their system did not have sufficient RAM
(64MiB) to decompress it.  However, that was a few years ago, and this
change adds only 16MiB, raising the requirement to 48MiB.

Besides, in a pinch, such users can always decompress on another system
and either operate directly on a recompressed (or uncompressed) tarball.

What do you think?
-----------------

* cfg.mk (XZ_OPT): Increase compression level to 9, yet with only 48MiB
dictionary size (the default with -9 would have been 64MiB). This gets
all but 1k worth of gain with only 16MiB additional decompression-time
memory requirement over -8's default of 32MiB.  Also, add pb=0.  It is
good for any US-ASCII, UTF-8, or ISO-8859-* text or other byte-aligned
data. The default is pb=2 i.e. 2^2 = 4-byte alignment which seems to
be the best compromise for unknown data.  The result: decreases the
size of the distributed .tar.xz file by 2.6% (aka 150KiB). While 49MiB
would have yielded an addition 1KiB decrease, that would have resulted
in encoding a dictionary size (in its 6-bit field) of 64MiB.
Based on a suggestion and explanation from Lasse Collin.
---
 cfg.mk | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/cfg.mk b/cfg.mk
index 7e28d9c..8a87c2a 100644
--- a/cfg.mk
+++ b/cfg.mk
@@ -46,7 +46,7 @@ export VERBOSE = yes
 # 5010604 9
 # 4923016 8e
 # 4914152 9e
-export XZ_OPT = -8e
+export XZ_OPT = --lzma2=preset=9e,dict=48MiB,pb=0

 old_NEWS_hash = 33e0d81904e66223883c8bc33c29a772

-- 
2.9.3