test: specialize OOM check for AIX

test/addons/addon.status

@@ -3,17 +3,3 @@ prefix addons
 [true] # This section applies to all platforms
 
 [$system==aix]
-# https://github.com/nodejs/build/issues/1820#issuecomment-505998851
-# https://github.com/nodejs/node/pull/28469
-# https://github.com/nodejs/node/pull/28516
-stringbytes-external-exceed-max/test-stringbytes-external-exceed-max.js: SKIP
-
-# https://github.com/nodejs/node/pull/28516
-stringbytes-external-exceed-max/test-stringbytes-external-at-max: SKIP
-stringbytes-external-exceed-max/test-stringbytes-external-exceed-max-by-1-ascii: SKIP
-stringbytes-external-exceed-max/test-stringbytes-external-exceed-max-by-1-base64: SKIP
-stringbytes-external-exceed-max/test-stringbytes-external-exceed-max-by-1-binary: SKIP
-stringbytes-external-exceed-max/test-stringbytes-external-exceed-max-by-1-hex: SKIP
-stringbytes-external-exceed-max/test-stringbytes-external-exceed-max-by-1-utf8: SKIP
-stringbytes-external-exceed-max/test-stringbytes-external-exceed-max-by-2: SKIP
-stringbytes-external-exceed-max/test-stringbytes-external-exceed-max: SKIP

test/addons/stringbytes-external-exceed-max/binding.cc

@@ -2,12 +2,42 @@
 #include <node.h>
 #include <v8.h>
 
+#ifdef _AIX
+// AIX allows over-allocation, and will SIGKILL when the allocated pages are
+// used if there is not enough VM. Check for available space until
+// out-of-memory.  Don't allow more then some (large) proportion of it to be
+// used for the test strings, so Node & V8 have some space for allocations.
+#include <signal.h>
+#include <sys/vminfo.h>
+
+static void* Allowed(size_t size) {
+  blkcnt_t allowedBlocks = psdanger(SIGKILL);
+
+  if (allowedBlocks < 1) {
+    // Already OOM
+    return nullptr;
+  }
+  const size_t BYTES_PER_BLOCK = 512;
+  size_t allowed = (allowedBlocks * BYTES_PER_BLOCK * 4) / 5;
+  if (size < allowed) {
+    return malloc(size);
+  }
+  return nullptr;
+}
+#else
+// Other systems also allow over-allocation, but this malloc-and-free approach
+// seems to be working for them.
+static void* Allowed(size_t size) {
+  return malloc(size);
+}
+#endif  // _AIX
+
 void EnsureAllocation(const v8::FunctionCallbackInfo<v8::Value> &args) {
   v8::Isolate* isolate = args.GetIsolate();
   uintptr_t size = args[0].As<v8::Integer>()->Value();
   v8::Local<v8::Boolean> success;
 
-  void* buffer = malloc(size);
+  void* buffer = Allowed(size);
   if (buffer) {
     success = v8::Boolean::New(isolate, true);
     free(buffer);