Add OCaml 5.5 implementation of gc_stats using word sized counters

.github/workflows/main.yml

@@ -13,6 +13,7 @@ jobs:
   build:
 
     strategy:
+      fail-fast: false
       matrix:
         ocaml-compiler:
           - 5.0
@@ -23,8 +24,16 @@ jobs:
         os:
           - ubuntu-latest
           - macos-15
+        include:
+          - ocaml-compiler: ocaml-base-compiler.5.5.0~alpha3
+            os: ubuntu-latest
+            experimental: true
+          - ocaml-compiler: ocaml-base-compiler.5.5.0~alpha3
+            os: macos-15
+            experimental: true
 
     runs-on: ${{ matrix.os }}
+    continue-on-error: ${{ matrix.experimental == true }}
 
     steps:
       - name: Checkout code

lib/olly_gc_stats/dune

@@ -18,3 +18,21 @@
   (>= %{ocaml_version} 5.3))
  (action
   (copy %{deps} %{target})))
+
+(rule
+ (deps gc_counters_shim.5.3.ml)
+ (target gc_counters_shim.ml)
+ (enabled_if
+  (and
+   (>= %{ocaml_version} 5.3)
+   (< %{ocaml_version} 5.5)))
+ (action
+  (copy %{deps} %{target})))
+
+(rule
+ (deps gc_counters_shim.5.5.ml)
+ (target gc_counters_shim.ml)
+ (enabled_if
+  (>= %{ocaml_version} 5.5))
+ (action
+  (copy %{deps} %{target})))

lib/olly_gc_stats/gc_counters_shim.5.3.ml

@@ -0,0 +1,16 @@
+(* OCaml 5.3 / 5.4: minor allocation counters report bytes, so convert to
+   words. EV_C_MAJOR_ALLOCATED_WORDS already reports words. *)
+let bytes_per_word = Sys.word_size / 8
+
+let runtime_counter ~domain_minor_words ~domain_promoted_words
+    ~domain_major_words ring_id _ts counter_type value =
+  match counter_type with
+  | Runtime_events.EV_C_MINOR_PROMOTED ->
+      domain_promoted_words.(ring_id) <-
+        domain_promoted_words.(ring_id) + (value / bytes_per_word)
+  | Runtime_events.EV_C_MINOR_ALLOCATED ->
+      domain_minor_words.(ring_id) <-
+        domain_minor_words.(ring_id) + (value / bytes_per_word)
+  | Runtime_events.EV_C_MAJOR_ALLOCATED_WORDS ->
+      domain_major_words.(ring_id) <- domain_major_words.(ring_id) + value
+  | _ -> ()

lib/olly_gc_stats/gc_counters_shim.5.5.ml

@@ -0,0 +1,14 @@
+(* OCaml 5.5+: prefer the word-sized minor counters added in ocaml/ocaml#14189.
+   The legacy bytes counters (EV_C_MINOR_ALLOCATED / EV_C_MINOR_PROMOTED) are
+   still emitted for backwards compatibility — we must ignore them here to
+   avoid double-counting. *)
+let runtime_counter ~domain_minor_words ~domain_promoted_words
+    ~domain_major_words ring_id _ts counter_type value =
+  match counter_type with
+  | Runtime_events.EV_C_MINOR_PROMOTED_WORDS ->
+      domain_promoted_words.(ring_id) <- domain_promoted_words.(ring_id) + value
+  | Runtime_events.EV_C_MINOR_ALLOCATED_WORDS ->
+      domain_minor_words.(ring_id) <- domain_minor_words.(ring_id) + value
+  | Runtime_events.EV_C_MAJOR_ALLOCATED_WORDS ->
+      domain_major_words.(ring_id) <- domain_major_words.(ring_id) + value
+  | _ -> ()

lib/olly_gc_stats/olly_gc_stats.5.3.ml

@@ -404,25 +404,9 @@ let gc_stats poll_sleep json output runtime_events_dir runtime_events_log_wsize
         domain_gc_times.(ring_id) <- domain_gc_times.(ring_id) + latency
     | _ -> ()
   in
-  (* TODO: OCaml 5.5 adds EV_C_MINOR_PROMOTED_WORDS and
-     EV_C_MINOR_ALLOCATED_WORDS (ocaml/ocaml#14189) which report in words
-     directly, replacing the bytes-to-words conversion below. *)
-  let bytes_per_word = Sys.word_size / 8 in
-  let runtime_counter ring_id _ts counter_type value =
-    match counter_type with
-    | Runtime_events.EV_C_MINOR_PROMOTED ->
-        (* Reported as bytes, convert to words *)
-        domain_promoted_words.(ring_id) <-
-          domain_promoted_words.(ring_id) + (value / bytes_per_word)
-    | Runtime_events.EV_C_MINOR_ALLOCATED ->
-        (* Reported as bytes, convert to words *)
-        domain_minor_words.(ring_id) <-
-          domain_minor_words.(ring_id) + (value / bytes_per_word)
-    | Runtime_events.EV_C_MAJOR_ALLOCATED_WORDS ->
-        (* Allocations to the major heap of this Domain in words,
-          since the last major slice. *)
-        domain_major_words.(ring_id) <- domain_major_words.(ring_id) + value
-    | _ -> ()
+  let runtime_counter =
+    Gc_counters_shim.runtime_counter ~domain_minor_words ~domain_promoted_words
+      ~domain_major_words
   in
 
   let init = Fun.id in