Hooks & modifications to GC to allow registration of externally allocated memory.

Goal: allow a mechanism to make the GC aware of non-Julia process memory usage.

Background in RAI-7988

  * Adds calls to register allocations and frees of process memory
    unaccounted for by live Julia objects, but relevant for GC
    collection heuristics.

  * Adds a separate call to allow the Julia program to adjust the
    `default_collect_interval`.

  * Increases the default collection interval (to avoid excessive
    full sweeps once external memory is reported)

Author: Ryan Daum

src/gc.c

@@ -604,10 +604,10 @@ static void gc_sweep_foreign_objs(void)
 static int64_t last_gc_total_bytes = 0;
 
 #ifdef _P64
-#define default_collect_interval (5600*1024*sizeof(void*))
+static size_t default_collect_interval = (5600*1024*sizeof(void*));
 static size_t max_collect_interval = 1250000000UL;
 #else
-#define default_collect_interval (3200*1024*sizeof(void*))
+static size_t default_collect_interval = (3200*1024*sizeof(void*));
 static size_t max_collect_interval =  500000000UL;
 #endif
 
@@ -1096,6 +1096,54 @@ void jl_gc_count_allocd(size_t sz) JL_NOTSAFEPOINT
         jl_atomic_load_relaxed(&ptls->gc_num.allocd) + sz);
 }
 
+JL_DLLEXPORT void jl_gc_set_default_collect_interval(size_t collect_interval) JL_NOTSAFEPOINT {
+    default_collect_interval = collect_interval;
+}
+
+JL_DLLEXPORT size_t jl_gc_default_collect_interval() JL_NOTSAFEPOINT {
+    return default_collect_interval;
+}
+
+JL_DLLEXPORT void jl_gc_allocd_external(size_t sz_delta) JL_NOTSAFEPOINT
+{
+    // External memory is divided up for accounting among all threads; this way the
+    // per-thread quantity is kept balanced to help avoid full GC thrashing if only one
+    // thread goes over max_collect_interval.
+    int64_t per_tls_delta = sz_delta / jl_n_threads;
+    int64_t remainder = sz_delta % jl_n_threads;
+
+    for (int i = 0; i < jl_n_threads; i++) {
+        jl_ptls_t ptls = jl_all_tls_states[i];
+        jl_atomic_store_relaxed(&ptls->gc_num.allocd,
+                                jl_atomic_load_relaxed(&ptls->gc_num.allocd) +
+                                    per_tls_delta);
+    }
+    // Stash the remainder in the 1st thread.
+    jl_ptls_t ptls = jl_all_tls_states[0];
+    jl_atomic_store_relaxed(&ptls->gc_num.allocd,
+                            jl_atomic_load_relaxed(&ptls->gc_num.allocd) + remainder);
+}
+
+JL_DLLEXPORT void jl_gc_freed_external(size_t sz_delta) JL_NOTSAFEPOINT
+{
+    // External memory is divided up for accounting among all threads; this way the
+    // per-thread quantity is kept balanced to help avoid full GC thrashing if only one
+    // thread goes over max_collect_interval.
+    int64_t per_tls_delta = sz_delta / jl_n_threads;
+    int64_t remainder = sz_delta % jl_n_threads;
+
+    for (int i = 0; i < jl_n_threads; i++) {
+        jl_ptls_t ptls = jl_all_tls_states[i];
+        jl_atomic_store_relaxed(&ptls->gc_num.freed,
+                                jl_atomic_load_relaxed(&ptls->gc_num.freed) +
+                                    per_tls_delta);
+    }
+    // Subtract the remainder from the 1st thread.
+    jl_ptls_t ptls = jl_all_tls_states[0];
+    jl_atomic_store_relaxed(&ptls->gc_num.freed,
+                            jl_atomic_load_relaxed(&ptls->gc_num.freed) + remainder);
+}
+
 static void combine_thread_gc_counts(jl_gc_num_t *dest) JL_NOTSAFEPOINT
 {
     for (int i = 0; i < jl_n_threads; i++) {

src/julia.h

@@ -937,6 +937,15 @@ JL_DLLEXPORT void *jl_gc_managed_realloc(void *d, size_t sz, size_t oldsz,
                                          int isaligned, jl_value_t *owner);
 JL_DLLEXPORT void jl_gc_safepoint(void);
 
+JL_DLLEXPORT void jl_gc_set_default_collect_interval(size_t collect_interval) JL_NOTSAFEPOINT;
+JL_DLLEXPORT size_t jl_gc_default_collect_interval(void) JL_NOTSAFEPOINT;
+
+// Record accounting for memory that exists outside-of the Julia runtime, but which is
+// nevertheless part of the same process RSS and which should be accounted for when
+// calculating process memory pressure when triggering garbage collection.
+JL_DLLEXPORT void jl_gc_allocd_external(size_t sz_delta) JL_NOTSAFEPOINT;
+JL_DLLEXPORT void jl_gc_freed_external(size_t sz_delta) JL_NOTSAFEPOINT;
+
 // object accessors -----------------------------------------------------------
 
 #define jl_svec_len(t)              (((jl_svec_t*)(t))->length)