Add API to disable full collections

src/gc-interface.h

@@ -142,8 +142,15 @@ JL_DLLEXPORT void jl_gc_set_max_memory(uint64_t max_mem);
 JL_DLLEXPORT void jl_gc_collect(jl_gc_collection_t collection);
 // Returns whether the thread with `tid` is a collector thread
 JL_DLLEXPORT int gc_is_collector_thread(int tid) JL_NOTSAFEPOINT;
+// Enables or disables automatic full (non-generational) collections.
+// When disabled (on == 0), automatic collections will only be incremental
+// (young generation only). Explicit full collections via jl_gc_collect(JL_GC_FULL)
+// are still honored. Returns whether automatic full collections were previously enabled.
+JL_DLLEXPORT int jl_gc_enable_auto_full_collection(int on);
+// Returns whether automatic full (non-generational) collections are enabled.
+JL_DLLEXPORT int jl_gc_auto_full_collection_is_enabled(void);
 // Returns which GC implementation is being used and possibly its version according to the list of supported GCs
-// NB: it should clearly identify the GC by including e.g. ‘stock’ or ‘mmtk’ as a substring.
+// NB: it should clearly identify the GC by including e.g. 'stock' or 'mmtk' as a substring.
 JL_DLLEXPORT const char* jl_gc_active_impl(void);
 // Sweep Julia's stack pools and mtarray buffers. Note that this function has been added to the interface as
 // each GC should implement it but it will most likely not be used by other code in the runtime.

src/gc-mmtk.c

@@ -337,6 +337,18 @@ JL_DLLEXPORT const char* jl_gc_active_impl(void) {
     return mmtk_version;
 }
 
+JL_DLLEXPORT int jl_gc_enable_auto_full_collection(int on)
+{
+    // MMTk does not currently support collection type control
+    return 1;
+}
+
+JL_DLLEXPORT int jl_gc_auto_full_collection_is_enabled(void)
+{
+    return 1;
+}
+
+
 int64_t last_gc_total_bytes = 0;
 int64_t last_live_bytes = 0; // live_bytes at last collection
 int64_t live_bytes = 0;

src/gc-stock.c

@@ -208,6 +208,7 @@ int prev_sweep_full = 1;
 int current_sweep_full = 0;
 int next_sweep_full = 0;
 int under_pressure = 0;
+int gc_disable_auto_full_sweep = 0; // when set, automatic full collections are inhibited
 
 // Full collection heuristics
 static int64_t live_bytes = 0;
@@ -3177,6 +3178,9 @@ static int _jl_gc_collect(jl_ptls_t ptls, jl_gc_collection_t collection) JL_NOTS
         recollect = 1;
         gc_record_full_sweep_reason(FULL_SWEEP_REASON_FORCED_FULL_SWEEP);
     }
+    if (gc_disable_auto_full_sweep && collection != JL_GC_FULL) {
+        sweep_full = 0;
+    }
     // 5. start sweeping
     uint64_t start_sweep_time = jl_hrtime();
     JL_PROBE_GC_SWEEP_BEGIN(sweep_full);
@@ -4151,6 +4155,18 @@ JL_DLLEXPORT const char* jl_gc_active_impl(void) {
     return "Built with stock GC";
 }
 
+JL_DLLEXPORT int jl_gc_enable_auto_full_collection(int on)
+{
+    int prev = !gc_disable_auto_full_sweep;
+    gc_disable_auto_full_sweep = (on == 0);
+    return prev;
+}
+
+JL_DLLEXPORT int jl_gc_auto_full_collection_is_enabled(void)
+{
+    return !gc_disable_auto_full_sweep;
+}
+
 #ifdef __cplusplus
 }
 #endif