build-node: Run GC as Shepherd timers.

* build-node.scm (garbage-collector-jobs): Remove.
(garbage-collector-service): New procedure.
(%garbage-collector-services): New variable.
<top level>: Use them instead of the ‘mcron-service-type’ extension.

build-node.scm

@@ -5,7 +5,7 @@
 (use-modules (gnu)
              (srfi srfi-1))
 (use-service-modules admin avahi base cuirass mcron networking
-                     ssh virtualization)
+                     shepherd ssh virtualization)
 (use-package-modules certs screen ssh)
 (use-modules ((cuirass-package) #:prefix latest:))
 
@@ -36,16 +36,40 @@
                         ;; We have 24 to 32 cores.
                         (extra-options '("--max-jobs=4" "--cores=8"))))))
 
-(define garbage-collector-jobs
-  ;; Collect garbage several times a day, with a bigger collection at 5AM.
-  (list #~(job '(next-hour '(5))
-               "guix gc -F 50G -d 2m")
-        #~(job '(next-hour '(10))
-               "guix gc -F 15G")
-        #~(job '(next-hour '(15))
-               "guix gc -F 25G")
-        #~(job '(next-hour '(20))
-               "guix gc -F 15G")))
+(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 '(0)
+                                                     #:hours '#$(iota 12 0 2))
+                                   15)
+        (garbage-collector-service 'gc
+                                   #~(calendar-event #:minutes '(0)
+                                                     #:hours '(5 15))
+                                   50)))
 
 
 (operating-system
@@ -103,8 +127,6 @@
                            (platforms (lookup-qemu-platforms "arm"
                                                              "aarch64"
                                                              "ppc64le"
-                                                             "riscv64"))))
-
-                 (simple-service 'gc-jobs mcron-service-type
-                                 garbage-collector-jobs))
+                                                             "riscv64")))))
+           %garbage-collector-services
            %custom-base-services)))