Report RSS and the commit charge on Windows

lib/harness.rb

@@ -73,6 +73,8 @@ def get_rss
     # First, grab a line like "62796 kB". Checking the Linux kernel source, Rss will always be in kB.
     rss_desc = File.read(mem_rollup_file).lines.detect { |line| line.start_with?("Rss") }.split(":", 2)[1][/(\d+)/, 1]
     1024 * Integer(rss_desc)
+  elsif defined?(WindowsMemoryCounters)
+    WindowsMemoryCounters.read&.fetch(:working_set) || 0
   else
     # Collect our own peak mem usage as soon as reasonable after finishing the last iteration.
     # This method is only accurate to kilobytes, but is nicely portable and doesn't require
@@ -163,7 +165,12 @@ def macos_resident_size
   buffer[RI_RESIDENT_SIZE_OFFSET, 8].unpack1('Q')
 end
 
+# Loaded after load_fiddle is defined, since it calls it right away.
+require_relative "harness/windows_memory_counters" if RUBY_PLATFORM.match?(/mswin|mingw/)
+
 def get_maxrss
+  return WindowsMemoryCounters.read&.fetch(:peak_working_set) if defined?(WindowsMemoryCounters)
+
   load_fiddle
 
   require 'rbconfig/sizeof'
@@ -221,6 +228,10 @@ def return_results(warmup_iterations, bench_iterations, **extra)
   if maxrss = get_maxrss
     ruby_bench_results["maxrss"] = maxrss
   end
+  if defined?(WindowsMemoryCounters) && (counters = WindowsMemoryCounters.read)
+    ruby_bench_results["commit_charge"] = counters[:commit_charge]
+    ruby_bench_results["peak_commit_charge"] = counters[:peak_commit_charge]
+  end
 
   # If YJIT or ZJIT is enabled, show some of its stats unless it does by itself.
   if yjit_stats

lib/harness/windows_memory_counters.rb

@@ -0,0 +1,34 @@
+# frozen_string_literal: true
+
+# Resolved when the harness loads, before use_gemfile. Loading fiddle after Bundler.setup goes through Bundler.reset!,
+# which redefines Kernel#gem and invalidates YJIT code if it happens between iterations. A dropped Fiddle::Handle is
+# freed by a deferred finalizer, whose interrupt also sends YJIT code back to the interpreter, so kernel32 stays open.
+module WindowsMemoryCounters
+  begin
+    load_fiddle
+    @kernel32 = Fiddle.dlopen("kernel32")
+    @process = Fiddle::Function.new(@kernel32['GetCurrentProcess'], [], Fiddle::TYPE_VOIDP).call
+    @get_info = Fiddle::Function.new(@kernel32['K32GetProcessMemoryInfo'], [Fiddle::TYPE_VOIDP, Fiddle::TYPE_VOIDP, Fiddle::TYPE_INT], Fiddle::TYPE_INT)
+  rescue LoadError, Fiddle::DLError, NameError
+    warn "Failed to get memory counters: #{$!.message}"
+  end
+
+  # Memory counters of this process in bytes. The working set is the Windows counterpart of RSS,
+  # and the commit charge (PagefileUsage) is the private memory the process has committed.
+  def self.read
+    return nil unless @get_info
+
+    # PROCESS_MEMORY_COUNTERS: two DWORDs followed by eight SIZE_Ts.
+    buffer = "\0".b * (8 + 8 * Fiddle::SIZEOF_SIZE_T)
+    buffer[0, 4] = [buffer.bytesize].pack('L')
+    return nil if @get_info.call(@process, buffer, buffer.bytesize).zero?
+
+    peak_working_set, working_set, _, _, _, _, commit_charge, peak_commit_charge = buffer.unpack('x8J8')
+    {
+      working_set: working_set,
+      peak_working_set: peak_working_set,
+      commit_charge: commit_charge,
+      peak_commit_charge: peak_commit_charge,
+    }
+  end
+end