Record the commit charge on Windows

Changes in private memory on Windows show up in the commit charge (PagefileUsage of GetProcessMemoryInfo) more than in the working set. The result JSON keeps it and its peak as commit_charge and peak_commit_charge.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

Author: hsbt

lib/harness.rb

@@ -228,6 +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

@@ -13,16 +13,22 @@ module WindowsMemoryCounters
     warn "Failed to get memory counters: #{$!.message}"
   end
 
-  # The working set of this process and its peak in bytes, the Windows counterparts of RSS and max RSS.
+  # 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, the first two being PeakWorkingSetSize and WorkingSetSize.
+    # 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 = buffer.unpack('x8J2')
-    { working_set: working_set, peak_working_set: peak_working_set }
+    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