Adding 'slab' info to virtual_memory

docs/index.rst

@@ -266,6 +266,7 @@ Memory
   - **active** *(UNIX)*: memory currently in use or very recently used, and so
     it is in RAM.
   - **inactive** *(UNIX)*: memory that is marked as not used.
+  - **slab** *(Linux)*: in-kernel data structures cache.
   - **buffers** *(Linux, BSD)*: cache for things like file system metadata.
   - **cached** *(Linux, BSD)*: cache for various things.
   - **shared** *(Linux, BSD)*: memory that may be simultaneously accessed by
@@ -284,7 +285,7 @@ Memory
   >>> import psutil
   >>> mem = psutil.virtual_memory()
   >>> mem
-  svmem(total=10367352832, available=6472179712, percent=37.6, used=8186245120, free=2181107712, active=4748992512, inactive=2758115328, buffers=790724608, cached=3500347392, shared=787554304)
+  svmem(total=10367352832, available=6472179712, percent=37.6, used=8186245120, free=2181107712, active=4748992512, inactive=2758115328, buffers=790724608, cached=3500347392, shared=787554304, slab=199348224)
   >>>
   >>> THRESHOLD = 100 * 1024 * 1024  # 100MB
   >>> if mem.available <= THRESHOLD:

psutil/_pslinux.py

@@ -149,7 +149,7 @@ class IOPriority(enum.IntEnum):
 # psutil.virtual_memory()
 svmem = namedtuple(
     'svmem', ['total', 'available', 'percent', 'used', 'free',
-              'active', 'inactive', 'buffers', 'cached', 'shared'])
+              'active', 'inactive', 'buffers', 'cached', 'shared', 'slab'])
 # psutil.disk_io_counters()
 sdiskio = namedtuple(
     'sdiskio', ['read_count', 'write_count',
@@ -441,6 +441,11 @@ def virtual_memory():
             inactive = 0
             missing_fields.append('inactive')
 
+    try:
+        slab = mems[b"Slab:"]
+    except KeyError:
+        slab = 0
+
     used = total - free - cached - buffers
     if used < 0:
         # May be symptomatic of running within a LCX container where such
@@ -481,7 +486,7 @@ def virtual_memory():
         warnings.warn(msg, RuntimeWarning)
 
     return svmem(total, avail, percent, used, free,
-                 active, inactive, buffers, cached, shared)
+                 active, inactive, buffers, cached, shared, slab)
 
 
 def swap_memory():

psutil/tests/test_linux.py

@@ -237,6 +237,31 @@ def test_available(self):
                 free_value, psutil_value, delta=MEMORY_TOLERANCE,
                 msg='%s %s \n%s' % (free_value, psutil_value, out))
 
+    def test_slab(self):
+        # Emulate /proc/meminfo because neither vmstat nor free return slab.
+        def open_mock(name, *args, **kwargs):
+            if name == '/proc/meminfo':
+                return io.BytesIO(textwrap.dedent("""\
+                    Active(anon):    6145416 kB
+                    Active(file):    2950064 kB
+                    Inactive(anon):   574764 kB
+                    Inactive(file):  1567648 kB
+                    MemAvailable:         -1 kB
+                    MemFree:         2057400 kB
+                    MemTotal:       16325648 kB
+                    SReclaimable:     346648 kB
+                    Slab:             186836 kB
+                    """).encode())
+            else:
+                return orig_open(name, *args, **kwargs)
+
+        orig_open = open
+        patch_point = 'builtins.open' if PY3 else '__builtin__.open'
+        with mock.patch(patch_point, create=True, side_effect=open_mock) as m:
+            ret = psutil.virtual_memory()
+            assert m.called
+            self.assertEqual(ret.slab, 191320064)
+
     def test_warnings_on_misses(self):
         # Emulate a case where /proc/meminfo provides few info.
         # psutil is supposed to set the missing fields to 0 and
@@ -280,6 +305,7 @@ def open_mock(name, *args, **kwargs):
                 self.assertEqual(ret.shared, 0)
                 self.assertEqual(ret.buffers, 0)
                 self.assertEqual(ret.available, 0)
+                self.assertEqual(ret.slab, 0)
 
     def test_avail_old_percent(self):
         # Make sure that our calculation of avail mem for old kernels