feat: add compatibility for zfs arc architectures, (matches htop sour…

…ce code)

Signed-off-by: Hudson Gerwing <grownuphudson@gmail.com>

psutil/_pslinux.py

@@ -171,6 +171,10 @@ class IOPriority(enum.IntEnum):
 svmem = namedtuple(
     'svmem', ['total', 'available', 'percent', 'used', 'free',
               'active', 'inactive', 'buffers', 'cached', 'shared', 'slab'])
+# psutil.zfs_arc_stats()
+szfsarc = namedtuple(
+    'szfsarc', ['enabled', 'min', 'max', 'compressed', 'uncompressed',
+                'size', 'header', 'anon', 'mfu', 'mru', 'other'])
 # psutil.disk_io_counters()
 sdiskio = namedtuple(
     'sdiskio', ['read_count', 'write_count',
@@ -415,13 +419,15 @@ def calculate_avail_vmem(mems):
     return int(avail)
 
 
-def virtual_memory():
+def virtual_memory(bool:include_zfs_arc=False):
     """Report virtual memory stats.
-    This implementation mimicks procps-ng-3.3.12, aka "free" CLI tool:
+    This implementation mimics procps-ng-3.3.12, aka "free" CLI tool:
     https://gitlab.com/procps-ng/procps/blob/
         24fd2605c51fccc375ab0287cec33aa767f06718/proc/sysinfo.c#L778-791
     The returned values are supposed to match both "free" and "vmstat -s"
     CLI tools.
+    If specifying the `include_zfs_arc` parameter, the implementation mimics
+    "htop" CLI tool instead of "free" CLI tool.
     """
     missing_fields = []
     mems = {}
@@ -523,6 +529,22 @@ def virtual_memory():
         #     24fd2605c51fccc375ab0287cec33aa767f06718/proc/sysinfo.c#L764
         avail = free
 
+    # ZFS ARC memory consumption is not reported by /proc/meminfo.
+    # Specifying `include_zfs_arc` will include reclaimable ZFS ARC
+    # memory in the returned values.
+    # N.B. this will make psutil match the output of "htop" instead
+    # of "free" CLI tool.
+    # See:
+    # https://www.reddit.com/r/zfs/comments/ha0p7f/understanding_arcstat_and_free/
+    # https://github.com/openzfs/zfs/issues/10255
+    if include_zfs_arc:
+        zfs = zfs_arc_stats()
+        if zfs.enabled:
+            shrinkable_size = max(zfs.size - zfs.min, 0)
+            used -= shrinkable_size
+            cached += shrinkable_size
+            avail += shrinkable_size
+
     percent = usage_percent((total - avail), total, round_=1)
 
     # Warn about missing metrics which are set to 0.
@@ -603,6 +625,64 @@ def swap_memory():
     return _common.sswap(total, used, free, percent, sin, sout)
 
 
+def zfs_arc_stats():
+    """Return ZFS ARC (Adaptive Replacement Cache) stats."""
+    missing_fields = []
+    mems = {}
+
+    def get_if_available(key):
+        try:
+            return mems[key] / 1024
+        except KeyError:
+            missing_fields.append(key)
+            return 0
+
+
+    with open_binary('%s/spl/kstat/zfs/arcstats' % get_procfs_path()) as f:
+        for line in f:
+            fields = line.split()
+            mems[fields[0]] = int(fields[1])
+
+    zfs_min = get_if_available(b'c_min')
+    zfs_max = get_if_available(b'c_max')
+    zfs_compressed = get_if_available(b'compressed_size')
+    zfs_uncompressed = get_if_available(b'uncompressed_size')
+    zfs_size = get_if_available(b'size')
+    zfs_header = get_if_available(b'hdr_size')
+    dbuf_size = get_if_available(b'dbuf_size')
+    dnode_size = get_if_available(b'dnode_size')
+    bonus_size = get_if_available(b'bonus_size')
+    zfs_anon = get_if_available(b'anon_size')
+    zfs_mfu = get_if_available(b'mfu_size')
+    zfs_mru = get_if_available(b'mru_size')
+
+    zfs_enabled = zfs.size > 0
+    zfs_other = dbuf_size + dnode_size + bonus_size if all([dbuf_size, dnode_size, bonus_size]) else 0
+
+    # Warn about missing metrics which are set to 0.
+    if missing_fields:
+        msg = "%s memory stats couldn't be determined and %s set to 0" % (
+            ", ".join(missing_fields),
+            "was" if len(missing_fields) == 1 else "were",
+        )
+        warnings.warn(msg, RuntimeWarning, stacklevel=2)
+
+    return szfsarc(
+        zfs_enabled,
+        zfs_min,
+        zfs_max,
+        zfs_compressed,
+        zfs_uncompressed,
+        zfs_size,
+        zfs_header,
+        zfs_anon,
+        zfs_mfu,
+        zfs_mru,
+        zfs_other
+    )
+
+
+
 # =====================================================================
 # --- CPU
 # =====================================================================