More efficiently create some vectors

And instrument the inferior memory after creating the gds-inferior-packages
vector.

guix-data-service/jobs/load-new-guix-revision.scm

@@ -541,8 +541,13 @@
            (/ (assoc-ref stats 'heap-size)
               (expt 2. 20)))))
 
-       (let ((vec (list->vector
+       (let ((vec (make-vector ,count)))
-                   (iota ,count ,start-index))))
+         (vector-fold
+          (lambda (i index _)
+            (vector-set! vec i index)
+            (1+ index))
+          ,start-index
+          vec)
          (vector-map!
           (lambda (_ index)
             (define package (vector-ref gds-inferior-packages index))
@@ -736,18 +741,30 @@
 
     (inferior-eval
      `(define gds-inferior-packages
-        (make-vector ,deduplicated-packages-length))
+        (vector ,@(map inferior-package-id deduplicated-packages)))
+     inf)
+    (inferior-eval
+     '(begin
+        (vector-map!
+         (lambda (_ id)
+           (or (hashv-ref %package-table id)
+               (error "missing package id")))
+         gds-inferior-packages)
+        #t)
      inf)
 
     (inferior-eval
-     `(for-each
+     '(let ((stats (gc-stats)))
-       (lambda (index id)
+        (simple-format
-         (vector-set! gds-inferior-packages
+         (current-error-port)
-                      index
+         "post gds-inferior-packages inferior heap: ~a MiB used (~a MiB heap)~%"
-                      (or (hashv-ref %package-table id)
+         (round
-                          (error "missing package id"))))
+          (/ (- (assoc-ref stats 'heap-size)
-       (iota ,deduplicated-packages-length)
+                (assoc-ref stats 'heap-free-size))
-       (list ,@(map inferior-package-id deduplicated-packages)))
+             (expt 2. 20)))
+         (round
+          (/ (assoc-ref stats 'heap-size)
+             (expt 2. 20)))))
      inf)
 
     (values (list->vector deduplicated-packages)