Re: Persistent heap usage when computing derivations

["Ludovic Courtès" <ludo@gnu.org>]

Hi Christopher,

Apologies for not answering earlier.

Christopher Baines <mail@cbaines.net> skribis:

> One of the memory problems I'm having relates to the Guix inferior
> processes that the data service uses when computing derivations. The
> data serivce goes through the list of systems (x86_64-linux,
> aarch64-linux, ...) and because the data cached for x86_64-linux
> probably doesn't relate to aarch64-linux, there's some code that
> attempts to clear the caches [1].
>
> 1: https://git.savannah.gnu.org/cgit/guix/data-service.git/tree/guix-data-service/jobs/load-new-guix-revision.scm#n1970
>
> Unfortunately this code has to reach in to Guix internals to try and do
> this, and it does reduce the heap usage significantly, but this doesn't
> result in stable memory usage. Each system processed seems to add about
> 250MiB of data to the Guile heap that isn't cleared out. To me that
> sounds like a lot of memory, but there's also a lot of systems/targets,
> so overall this leads to the inferior process using with around 6GiB of
> data in the heap after processing all the systems/targets. This peak
> memory usage really limits how much the machine can do.

Did you consider running one inferior per system type, as a way to
sidestep the problem?

This is what ‘cuirass evaluate’ does and it manages to run typically 4
of them in parallel (x86_64-linux, i686-linux, aarch64-linux, and
powerpc64le-linux).  Memory usage may be high but at least it’s not a
blocker.

  https://git.savannah.gnu.org/cgit/guix/guix-cuirass.git/tree/src/cuirass/scripts/evaluate.scm#n137

Ludo’.