[Windows] psutil.swap_memory() show swap instead of committed memory

Signed-off-by: David Knaack <davidkna@users.noreply.github.com>

CREDITS

@@ -740,3 +740,7 @@ I: 1851
 N: guille
 W: https://github.com/guille
 I: 1913
+
+N: David Knaack
+W: https://github.com/davidkna
+I: 1921

HISTORY.rst

@@ -22,6 +22,7 @@ XXXX-XX-XX
   called after sprintf().  (patch by alxchk)
 - 1874_: [Solaris] swap output error due to incorrect range.
 - 1913_: [Linux] wait_procs seemingly ignoring timeout, TimeoutExpired thrown
+- 1921_: [Windows] psutil.swap_memory() shows committed memory instead of swap
 
 5.8.0
 =====

psutil/_pswindows.py

@@ -241,8 +241,21 @@ def virtual_memory():
 def swap_memory():
     """Swap system memory as a (total, used, free, sin, sout) tuple."""
     mem = cext.virtual_mem()
-    total = mem[2]
-    free = mem[3]
+
+    total_phys = mem[0]
+    free_phys = mem[1]
+    total_system = mem[2]
+    free_system = mem[3]
+
+    # Despite the name PageFile refers to total system memory here
+    # thus physical memory values need to be substracted to get swap values
+    total = total_system - total_phys
+    if total <= 0:
+        total = 0
+    free = free_system - free_phys
+    if free <= 0:
+        free = 0
+
     used = total - free
     percent = usage_percent(used, total, round_=1)
     return _common.sswap(total, used, free, percent, 0, 0)