Get Windows percent swap usage from performance counters (#2160)

Signed-off-by: Daniel Widdis <widdis@gmail.com>

7 files changed, 88 insertions, 6 deletions

diff --git a/CREDITS b/CREDITS
index f4146360..c845a8c6 100644
--- a/CREDITS
+++ b/CREDITS
@@ -804,7 +804,7 @@ I: 2150
 
 N: Daniel Widdis
 W: https://github.com/dbwiddis
-I: 2077
+I: 2077, 2160
 
 N: Amir Rossert
 W: https://github.com/arossert
diff --git a/HISTORY.rst b/HISTORY.rst
index e82605d8..8d22111a 100644
--- a/HISTORY.rst
+++ b/HISTORY.rst
@@ -47,6 +47,8 @@
   ``SPEED_UNKNOWN`` definition.  (patch by Amir Rossert)
 - 2010_, [macOS]: on MacOS, arm64 ``IFM_1000_TX`` and ``IFM_1000_T`` are the
   same value, causing a build failure.  (patch by Lawrence D'Anna)
+- 2160_, [Windows]: Get Windows percent swap usage from performance counters.
+  (patch by Daniel Widdis)
 
 5.9.3
 =====
diff --git a/psutil/_psutil_windows.c b/psutil/_psutil_windows.c
index 2ed937ee..11176de7 100644
--- a/psutil/_psutil_windows.c
+++ b/psutil/_psutil_windows.c
@@ -1560,6 +1560,7 @@ PsutilMethods[] = {
     {"disk_usage", psutil_disk_usage, METH_VARARGS},
     {"getloadavg", (PyCFunction)psutil_get_loadavg, METH_VARARGS},
     {"getpagesize", psutil_getpagesize, METH_VARARGS},
+    {"swap_percent", psutil_swap_percent, METH_VARARGS},
     {"init_loadavg_counter", (PyCFunction)psutil_init_loadavg_counter, METH_VARARGS},
     {"net_connections", psutil_net_connections, METH_VARARGS},
     {"net_if_addrs", psutil_net_if_addrs, METH_VARARGS},
diff --git a/psutil/_pswindows.py b/psutil/_pswindows.py
index 3802f3ed..4081aa17 100644
--- a/psutil/_pswindows.py
+++ b/psutil/_pswindows.py
@@ -244,16 +244,22 @@ def swap_memory():
     mem = cext.virtual_mem()
 
     total_phys = mem[0]
-    free_phys = mem[1]
     total_system = mem[2]
-    free_system = mem[3]
 
     # system memory (commit total/limit) is the sum of physical and swap
     # thus physical memory values need to be substracted to get swap values
     total = total_system - total_phys
-    free = min(total, free_system - free_phys)
-    used = total - free
-    percent = usage_percent(used, total, round_=1)
+    # commit total is incremented immediately (decrementing free_system)
+    # while the corresponding free physical value is not decremented until
+    # pages are accessed, so we can't use free system memory for swap.
+    # instead, we calculate page file usage based on performance counter
+    if (total > 0):
+        percentswap = cext.swap_percent()
+        used = int(0.01 * percentswap * total)
+    else:
+        used = 0
+    free = total - used
+    percent = round(percentswap, 1)
     return _common.sswap(total, used, free, percent, 0, 0)
 
 
diff --git a/psutil/arch/windows/mem.c b/psutil/arch/windows/mem.c
index 18b535e6..24dc15ad 100644
--- a/psutil/arch/windows/mem.c
+++ b/psutil/arch/windows/mem.c
@@ -7,6 +7,7 @@
 #include <Python.h>
 #include <windows.h>
 #include <Psapi.h>
+#include <pdh.h>
 
 #include "../../_psutil_common.h"
 
@@ -41,3 +42,53 @@ psutil_virtual_mem(PyObject *self, PyObject *args) {
         totalSys,
         availSys);
 }
+
+
+// Return a float representing the percent usage of all paging files on
+// the system.
+PyObject *
+psutil_swap_percent(PyObject *self, PyObject *args) {
+    WCHAR *szCounterPath = L"\\Paging File(_Total)\\% Usage";
+    PDH_STATUS s;
+    HQUERY hQuery;
+    HCOUNTER hCounter;
+    PDH_FMT_COUNTERVALUE counterValue;
+    double percentUsage;
+
+    if ((PdhOpenQueryW(NULL, 0, &hQuery)) != ERROR_SUCCESS) {
+        PyErr_Format(PyExc_RuntimeError, "PdhOpenQueryW failed");
+        return NULL;
+    }
+
+    s = PdhAddEnglishCounterW(hQuery, szCounterPath, 0, &hCounter);
+    if (s != ERROR_SUCCESS) {
+        PdhCloseQuery(hQuery);
+        PyErr_Format(
+            PyExc_RuntimeError,
+            "PdhAddEnglishCounterW failed. Performance counters may be disabled."
+        );
+        return NULL;
+    }
+
+    s = PdhCollectQueryData(hQuery);
+    if (s != ERROR_SUCCESS) {
+        // If swap disabled this will fail.
+        psutil_debug("PdhCollectQueryData failed; assume swap percent is 0");
+        percentUsage = 0;
+    }
+    else {
+        s = PdhGetFormattedCounterValue(
+            (PDH_HCOUNTER)hCounter, PDH_FMT_DOUBLE, 0, &counterValue);
+        if (s != ERROR_SUCCESS) {
+            PdhCloseQuery(hQuery);
+            PyErr_Format(
+                PyExc_RuntimeError, "PdhGetFormattedCounterValue failed");
+            return NULL;
+        }
+        percentUsage = counterValue.doubleValue;
+    }
+
+    PdhRemoveCounter(hCounter);
+    PdhCloseQuery(hQuery);
+    return Py_BuildValue("d", percentUsage);
+}
diff --git a/psutil/arch/windows/mem.h b/psutil/arch/windows/mem.h
index a10781df..48d3dade 100644
--- a/psutil/arch/windows/mem.h
+++ b/psutil/arch/windows/mem.h
@@ -8,3 +8,4 @@
 
 PyObject *psutil_getpagesize(PyObject *self, PyObject *args);
 PyObject *psutil_virtual_mem(PyObject *self, PyObject *args);
+PyObject *psutil_swap_percent(PyObject *self, PyObject *args);
diff --git a/psutil/tests/test_windows.py b/psutil/tests/test_windows.py
index 9b163a18..a9f68933 100755
--- a/psutil/tests/test_windows.py
+++ b/psutil/tests/test_windows.py
@@ -162,6 +162,27 @@ class TestSystemAPIs(WindowsTestCase):
             int(w.AvailableBytes), psutil.virtual_memory().free,
             delta=TOLERANCE_SYS_MEM)
 
+    def test_total_swapmem(self):
+        w = wmi.WMI().Win32_PerfRawData_PerfOS_Memory()[0]
+        self.assertEqual(int(w.CommitLimit) - psutil.virtual_memory().total,
+                         psutil.swap_memory().total)
+        if (psutil.swap_memory().total == 0):
+            self.assertEqual(0, psutil.swap_memory().free)
+            self.assertEqual(0, psutil.swap_memory().used)
+
+    def test_percent_swapmem(self):
+        if (psutil.swap_memory().total > 0):
+            w = wmi.WMI().Win32_PerfRawData_PerfOS_PagingFile(
+                Name="_Total")[0]
+            # calculate swap usage to percent
+            percentSwap = int(w.PercentUsage) * 100 / int(w.PercentUsage_Base)
+            # exact percent may change but should be reasonable
+            # assert within +/- 5% and between 0 and 100%
+            self.assertGreaterEqual(psutil.swap_memory().percent, 0)
+            self.assertAlmostEqual(psutil.swap_memory().percent, percentSwap,
+                                   delta=5)
+            self.assertLessEqual(psutil.swap_memory().percent, 100)
+
     # @unittest.skipIf(wmi is None, "wmi module is not installed")
     # def test__UPTIME(self):
     #     # _UPTIME constant is not public but it is used internally