Fix heapsize hint and use a line for max memory

src/gc.c

@@ -3228,8 +3228,6 @@ void jl_init_thread_heap(jl_ptls_t ptls)
 // System-wide initializations
 void jl_gc_init(void)
 {
-    if (jl_options.heap_size_hint)
-        jl_gc_set_max_memory(jl_options.heap_size_hint);
 
     JL_MUTEX_INIT(&heapsnapshot_lock);
     JL_MUTEX_INIT(&finalizers_lock);
@@ -3253,8 +3251,15 @@ void jl_gc_init(void)
     uint64_t constrained_mem = uv_get_constrained_memory();
     if (constrained_mem > 0 && constrained_mem < total_mem)
         total_mem = constrained_mem;
-    max_total_memory = total_mem / 10 * 6;
+    double percent;
+    if (total_mem < 128e9)
+        percent = total_mem * 2.34375e-12 + 0.6; // 60% at 0 gigs and 90% at 128 to not
+    else                                         // overcommit too much on memory contrained devices
+        percent = 0.9;
+    max_total_memory = total_mem * percent;
 #endif
+    if (jl_options.heap_size_hint)
+        jl_gc_set_max_memory(jl_options.heap_size_hint);
 
     t_start = jl_hrtime();
 }
@@ -3267,6 +3272,11 @@ JL_DLLEXPORT void jl_gc_set_max_memory(uint64_t max_mem)
     }
 }
 
+JL_DLLEXPORT uint64_t jl_gc_get_max_memory(void)
+{
+    return max_total_memory;
+}
+
 // callback for passing OOM errors from gmp
 JL_DLLEXPORT void jl_throw_out_of_memory_error(void)
 {

src/jl_exported_funcs.inc

@@ -172,6 +172,7 @@
     XX(jl_gc_external_obj_hdr_size) \
     XX(jl_gc_find_taggedvalue_pool) \
     XX(jl_gc_get_total_bytes) \
+    XX(jl_gc_get_max_memory) \
     XX(jl_gc_internal_obj_base_ptr) \
     XX(jl_gc_is_enabled) \
     XX(jl_gc_live_bytes) \

src/julia.h

@@ -919,6 +919,7 @@ JL_DLLEXPORT void jl_free_stack(void *stkbuf, size_t bufsz);
 JL_DLLEXPORT void jl_gc_use(jl_value_t *a);
 // Set GC memory trigger in bytes for greedy memory collecting
 JL_DLLEXPORT void jl_gc_set_max_memory(uint64_t max_mem);
+JL_DLLEXPORT uint64_t jl_gc_get_max_memory(void);
 
 JL_DLLEXPORT void jl_clear_malloc_data(void);
 

test/cmdlineargs.jl

@@ -901,4 +901,6 @@ end
         @test lines[3] == "foo"
         @test lines[4] == "bar"
     end
+#heap-size-hint
+@test readchomp(`$(Base.julia_cmd()) --startup-file=no --heap-size-hint=500M -e "println(@ccall jl_gc_get_max_memory()::UInt64)"`) == "524288000"
 end