Calculate virtual_available in iware::system::memory() on Darwin

Closes #81

Author: nabijaczleweli

src/system/memory/memory_darwin.cpp

@@ -19,23 +19,21 @@
 iware::system::memory_t iware::system::memory() noexcept {
 	iware::system::memory_t ret{};
 
-	const auto host = mach_host_self();
-
 	const auto ctl_ram = iware::detail::sysctl(CTL_HW, HW_MEMSIZE);
 	if(!ctl_ram.empty()) {
 		const auto ram = iware::detail::deconstruct_sysctl_int(ctl_ram);
 		if(ram.first)
 			ret.virtual_total = ram.second;
 	}
 
-	vm_statistics64 stats;
-	natural_t count = HOST_VM_INFO64_COUNT;
-	if(host_statistics64(host, HOST_VM_INFO64, reinterpret_cast<host_info64_t>(&stats), &count) == KERN_SUCCESS)
-		ret.virtual_available = stats.free_count * getpagesize();
-
 	ret.physical_total     = ret.virtual_total;
 	ret.physical_available = ret.virtual_available;
 
+	std::uint32_t mem_free;
+	auto mem_free_length = sizeof(mem_free);
+	if(sysctlbyname("kern.memorystatus_level", &mem_free, &mem_free_length, nullptr, 0) != -1)
+		ret.virtual_available = mem_free * ret.virtual_total / 100;
+
 	return ret;
 }