(import (chicken gc) (chicken blob))
(let ([l '()]
      [stats (memory-statistics)])
  (define (alloc bytes)
    (gc #t)
    (print "alloc " bytes " expected used: "
           (+ (vector-ref (memory-statistics) 1) bytes))
    (set! l (cons (make-blob bytes) l)))

  (let lp ([i 0])
    (when (< i 50)
      (let ([bytes (inexact->exact
                    (floor (/ (vector-ref
                               (memory-statistics) 1) 20)))]
            [cur-used (vector-ref (memory-statistics) 1)])
        (alloc bytes)
        (let ([new-used (vector-ref (memory-statistics) 1)])
          (print "diff: " (- new-used (+ cur-used bytes)))))
      (let ([new (memory-statistics)])
        (print "used / heap: " (vector-ref new 1) " / " (vector-ref new 0)
               (if (= (vector-ref stats 0) (vector-ref new 0))
                   "" " <- heap grew"))
        (set! stats new))
      (lp (add1 i)))))

;; $ ./gctest 
;; alloc 51635 expected used: 1084355
;; diff: 37
;; used / heap: 1084304 / 1572864
;; alloc 54219 expected used: 1138611
;; diff: 37
;; used / heap: 1138560 / 1572864
;; alloc 56932 expected used: 1195580
;; diff: 36
;; used / heap: 1195528 / 1572864
;; alloc 59780 expected used: 1255396
;; diff: 36
;; used / heap: 1255344 / 1572864
;; alloc 62771 expected used: 1318203
;; diff: 37
;; used / heap: 1318152 / 1572864
;; alloc 65911 expected used: 1384151
;; diff: 33
;; used / heap: 1384096 / 1572864
;; alloc 69208 expected used: 1453392
;; diff: 32
;; used / heap: 1453336 / 1572864
;; alloc 72670 expected used: 1526094
;; diff: 34
;; used / heap: 1526040 / 1572864
;; alloc 76306 expected used: 1602434
;; diff: 1048614
;; used / heap: 2650960 / 3670016 <- heap grew
;; alloc 132552 expected used: 2783600
;; diff: 32
;; used / heap: 2783544 / 3670016
;; alloc 139181 expected used: 2922813
;; diff: 35
;; used / heap: 2922760 / 3670016
;; alloc 146142 expected used: 3068990
;; diff: 34
;; used / heap: 3068936 / 3670016
;; alloc 153450 expected used: 3222474
;; diff: 38
;; used / heap: 3222424 / 3670016
;; alloc 161125 expected used: 3383637
;; diff: 35
;; used / heap: 3383584 / 3670016
;; alloc 169183 expected used: 3552855
;; diff: 33
;; used / heap: 3552800 / 3670016
;; alloc 177644 expected used: 3730532
;; diff: 1835044
;; used / heap: 5565488 / 7340032 <- heap grew
;; alloc 278278 expected used: 5843854
;; diff: 34
;; used / heap: 5843800 / 7340032
;; alloc 292194 expected used: 6136082
;; diff: 38
;; used / heap: 6136032 / 7340032
;; alloc 306805 expected used: 6442925
;; diff: 35
;; used / heap: 6442872 / 7340032
;; alloc 322147 expected used: 6765107
;; diff: 37
;; used / heap: 6765056 / 7340032
;; alloc 338256 expected used: 7103400
;; diff: 32
;; used / heap: 7103344 / 7340032
;; alloc 355171 expected used: 7458603
;; diff: 3670053
;; used / heap: 11128568 / 14680064 <- heap grew
;; alloc 556432 expected used: 11685088
;; diff: 32
;; used / heap: 11685032 / 14680064
;; alloc 584255 expected used: 12269375
;; diff: 33
;; used / heap: 12269320 / 14680064
;; alloc 613470 expected used: 12882878
;; diff: 34
;; used / heap: 12882824 / 14680064
;; alloc 644145 expected used: 13527057
;; diff: 39
;; used / heap: 13527008 / 14680064
;; alloc 676354 expected used: 14203450
;; diff: 38
;; used / heap: 14203400 / 14680064
;; alloc 710174 expected used: 14913662
;; diff: 7340066
;; used / heap: 22253640 / 29360128 <- heap grew
;; alloc 1112686 expected used: 23366414
;; diff: 34
;; used / heap: 23366360 / 29360128
;; alloc 1168322 expected used: 24534770
;; diff: 38
;; used / heap: 24534720 / 29360128
;; alloc 1226740 expected used: 25761548
;; diff: 36
;; used / heap: 25761496 / 29360128
;; alloc 1288078 expected used: 27049662
;; diff: 34
;; used / heap: 27049608 / 29360128
;; alloc 1352484 expected used: 28402180
;; diff: 15356350
;; used / heap: 43758442 / 60072756 <- heap grew
;; alloc 2187926 expected used: 45946456
;; diff: 34
;; used / heap: 45946402 / 60072756
;; alloc 2297324 expected used: 48243814
;; diff: 36
;; used / heap: 48243762 / 60072756
;; alloc 2412192 expected used: 50656042
;; diff: 32
;; used / heap: 50655986 / 60072756
;; alloc 2532803 expected used: 53188877
;; diff: 37
;; used / heap: 53188826 / 60072756
;; alloc 2659445 expected used: 55848359
;; diff: 35
;; used / heap: 55848306 / 60072756
;; alloc 2792419 expected used: 58640813
;; diff: 37
;; used / heap: 58640762 / 60072756
;; alloc 2932042 expected used: 61572892
;; diff: 31502445
;; used / heap: 93075249 / 123077570 <- heap grew
;; alloc 4653766 expected used: 97729103
;; diff: 34
;; used / heap: 97729049 / 123077570
;; alloc 4886456 expected used: 102615593
;; diff: 32
;; used / heap: 102615537 / 123077570
;; alloc 5130780 expected used: 107746405
;; diff: 36
;; used / heap: 107746353 / 123077570
;; alloc 5387321 expected used: 113133762
;; diff: 39
;; used / heap: 113133713 / 123077570
;; alloc 5656689 expected used: 118790490
;; diff: 39
;; used / heap: 118790441 / 123077570
;; alloc 5939526 expected used: 124730055
;; diff: 64508590
;; used / heap: 189238557 / 252094682 <- heap grew
;; alloc 9461931 expected used: 198700576
;; diff: 37
;; used / heap: 198700525 / 252094682
;; alloc 9935030 expected used: 208635643
;; diff: 34
;; used / heap: 208635589 / 252094682
;; alloc 10431783 expected used: 219067460
;; diff: 33
;; used / heap: 219067405 / 252094682
;; alloc 10953374 expected used: 230020867
;; diff: 34
;; used / heap: 230020813 / 252094682