bug#48963: "guix build guix" halts after exhausting memory

[Julien Lepiller]

Hi Guix!

I tried updating my system on my armhf board (2GB of RAM), but during
"guix system reconfigure", guix tries to build itself (the guix package
from (gnu packages package-management)). This package uses too much
memory to build, and I start getting GC warnings like so:

GC Warning: Out of memory - trying to allocate requested amount (552
bytes)...
GC Warning: Header allocation failed: dropping block
GC Warning: Out of Memory! Heap size: 2571 MiB. Returning NULL!
Warning: Unwind-only out of memory exception; skipping pre-unwind
handler.

after some more progress and a lot more warnings, the build stops (CPU
is at 2%), but the memory is not freed. The build stayed stuck for a
long time until I decided to cancel it.

As a work-around, I tried using the guix-daemon package instead (by
changing the guix field in guix-configuration), but "guix system" still
wants to build the guix package anyway. I tried finding usages of the
guix package (grepping for "package-management" yields a relatively
short list of files, and none of them seems to be used by my config,
except (gnu services base) which always uses the guix from the
configuration). Why?

Can we instead break the build (at the Makefile level) into multiple
smaller chunks, that require less memory, in the same way (guix self)
works?