install/55751: alpha should use gz install sets rather than xz

[Izumi Tsutsui <tsutsui%ceres.dti.ne.jp@localhost>]

>Number:         55751
>Category:       install
>Synopsis:       alpha should use gz install sets rather than xz
>Confidential:   no
>Severity:       non-critical
>Priority:       medium
>Responsible:    install-manager
>State:          open
>Class:          change-request
>Submitter-Id:   net
>Arrival-Date:   Sat Oct 24 18:35:00 +0000 2020
>Originator:     Izumi Tsutsui
>Release:        NetBSD 9.1 and -current
>Organization:
>Environment:
System: NetBSD 9.1 and -current
Architecture: alpha
Machine: alpha
>Description:
NetBSD/alpha has been changed to "USE_XZ_SETS=yes" as other 64 bit ports:
 http://cvsweb.netbsd.org/bsdweb.cgi/src/share/mk/bsd.own.mk#rev1.1077

But at least on my DEC 3000/300 (21064 150MHz) there are several problems:

- gzip(1) gets "out of swap" during extracting base.tar.xz on sysinst.
  My DEC 3000 has 64MB but it is not enough for "xz -9", as noted in
  the xz(1) man page:
>>  For example, decompressing a file created with xz -9 currently requires
>>  65 MiB of memory.

- Even if sysinst is configured to use swap partition, extracting
  base.tar.xz and comp.tar.xz is really slow on my DEC 3000.
  (~100kB/sec; similar speed to extrace gzip sets on 68040 25MHz)

- Less benefits. I guess USE_XZ_SETS was introduce to make
  iso images small enough (to fit in 800MB CD size?), but current
  alpha's iso with USE_XZ_SETS=no is much smaller than that.
  (~300MB, and xz one is ~180MB; not sure this is reasonable though)

>How-To-Repeat:
See above. 

>Fix:
Just revert to set "USE_XZ_SET=no" for alpha?
Or relax the compress level of xz from -9?

---
Izumi Tsutsui