head-node: Turn GC jobs into Shepherd timers.

* head-node.scm (garbage-collector-service): New procedure.
(%garbage-collector-services): New variable.
<top level>: Remove ‘gc-jobs’ and use ‘%garbage-collector-services’
instead.

head-node.scm

@@ -57,12 +57,41 @@ export CUIRASS_LOGGING_LEVEL=${CUIRASS_LOGGING_LEVEL:-debug}\n"
                         ;; We have 24 cores.
                         (extra-options '("--max-jobs=2" "--cores=6"))))))
 
-(define garbage-collector-jobs
-  ;; Collect garbage at 5AM every day, and make sure we're on track at 3PM.
-  (list #~(job '(next-hour '(5))
-               "guix gc -F 25G -d 2m")
-        #~(job '(next-hour '(15))
-               "guix gc -F 15G")))
+;; TODO: Share with 'build-node.scm'.
+(define (garbage-collector-service name calendar free-space)
+  "Return a Shepherd timer called NAME that collects garbage according to
+CALENDAR, a gexp, and ensures at least FREE-SPACE GiB are available."
+  (simple-service
+   name shepherd-root-service-type
+   (list (shepherd-service
+          (provision (list name))
+          (requirement '(user-processes))
+          (modules '((shepherd service timer)))
+          (start #~(make-timer-constructor
+                    #$calendar
+                    (command '("/run/current-system/profile/bin/guix" "gc"
+                               "-F" #$(format #f "~aG" free-space)
+                               "-d" "2m"))
+                    #:wait-for-termination? #t))
+          (stop #~(make-timer-destructor))
+          (documentation "Run the garbage collector (GC).")
+          (actions
+           (list (shepherd-action
+                  (name 'trigger)
+                  (documentation "GC!")
+                  (procedure #~trigger-timer))))))))
+
+(define %garbage-collector-services
+  ;; Collect garbage several times a day, with bigger collections twice a
+  ;; day.
+  (list (garbage-collector-service 'gc-quick
+                                   #~(calendar-event #:minutes '(30)
+                                                     #:hours '#$(iota 24))
+                                   20)
+        (garbage-collector-service 'gc
+                                   #~(calendar-event #:minutes '(0)
+                                                     #:hours '(5 15))
+                                   60)))
 
 (define (guix-channel branch)
   #~(channel
@@ -496,9 +525,6 @@ export CUIRASS_LOGGING_LEVEL=${CUIRASS_LOGGING_LEVEL:-debug}\n"
                            (platforms (lookup-qemu-platforms "arm"
                                                              "aarch64"))))
 
-                 (simple-service 'gc-jobs mcron-service-type
-                                 garbage-collector-jobs)
-
                  (service cuirass-service-type
                           (cuirass-configuration
                            (cuirass cuirass-latest/debug)
@@ -541,4 +567,6 @@ export CUIRASS_LOGGING_LEVEL=${CUIRASS_LOGGING_LEVEL:-debug}\n"
                  ;; Stop Cuirass when disk space is low.
                  (service disk-space-watchdog-service-type
                           (list (* 1 GiB) (* 1 GiB))))
+
+           %garbage-collector-services
            %custom-base-services)))