writeback: add wb_monitor.py script to monitor writeback info on bdi

Add wb_monitor.py script to monitor writeback information on backing dev
which makes it easier and more convenient to observe writeback behaviors
of running system.

The wb_monitor.py script is written based on wq_monitor.py.

Following domain hierarchy is tested:
global domain (320G)
/ \
cgroup domain1(10G) cgroup domain2(10G)
| |
bdi wb1 wb2

The wb_monitor.py script output is as following:
./wb_monitor.py 252:16 -c
writeback reclaimable dirtied written avg_bw
252:16_1 0 0 0 0 102400
252:16_4284 672 820064 9230368 8410304 685612
252:16_4325 896 819840 10491264 9671648 652348
252:16 1568 1639904 19721632 18081952 1440360

writeback reclaimable dirtied written avg_bw
252:16_1 0 0 0 0 102400
252:16_4284 672 820064 9230368 8410304 685612
252:16_4325 896 819840 10491264 9671648 652348
252:16 1568 1639904 19721632 18081952 1440360
...

Link: https://lkml.kernel.org/r/[e-mail]
Signed-off-by: Kemeng Shi <[e-mail]>
Suggested-by: Tejun Heo <[e-mail]>
Cc: Brian Foster <[e-mail]>
Cc: David Howells <[e-mail]>
Cc: David Sterba <[e-mail]>
Cc: Jan Kara <[e-mail]>
Cc: Mateusz Guzik <[e-mail]>
Cc: Matthew Wilcox (Oracle) <[e-mail]>
Cc: SeongJae Park <[e-mail]>
Cc: Stephen Rothwell <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>

tools/writeback/wb_monitor.py

···
+#!/usr/bin/env drgn
+#
+# Copyright (C) 2024 Kemeng Shi <[e-mail]>
+# Copyright (C) 2024 Huawei Inc
+
+desc = """
+This is a drgn script based on wq_monitor.py to monitor writeback info on
+backing dev. For more info on drgn, visit https://github.com/osandov/drgn.
+
+  writeback(kB)     Amount of dirty pages are currently being written back to
+                    disk.
+
+  reclaimable(kB)   Amount of pages are currently reclaimable.
+
+  dirtied(kB)       Amount of pages have been dirtied.
+
+  wrttien(kB)       Amount of dirty pages have been written back to disk.
+
+  avg_wb(kBps)      Smoothly estimated write bandwidth of writing dirty pages
+                    back to disk.
+"""
+
+import signal
+import re
+import time
+import json
+
+import drgn
+from drgn.helpers.linux.list import list_for_each_entry
+
+import argparse
+parser = argparse.ArgumentParser(description=desc,
+                                 formatter_class=argparse.RawTextHelpFormatter)
+parser.add_argument('bdi', metavar='REGEX', nargs='*',
+                    help='Target backing device name patterns (all if empty)')
+parser.add_argument('-i', '--interval', metavar='SECS', type=float, default=1,
+                    help='Monitoring interval (0 to print once and exit)')
+parser.add_argument('-j', '--json', action='store_true',
+                    help='Output in json')
+parser.add_argument('-c', '--cgroup', action='store_true',
+                    help='show writeback of bdi in cgroup')
+args = parser.parse_args()
+
+bdi_list                = prog['bdi_list']
+
+WB_RECLAIMABLE          = prog['WB_RECLAIMABLE']
+WB_WRITEBACK            = prog['WB_WRITEBACK']
+WB_DIRTIED              = prog['WB_DIRTIED']
+WB_WRITTEN              = prog['WB_WRITTEN']
+NR_WB_STAT_ITEMS        = prog['NR_WB_STAT_ITEMS']
+
+PAGE_SHIFT              = prog['PAGE_SHIFT']
+
+def K(x):
+    return x << (PAGE_SHIFT - 10)
+
+class Stats:
+    def dict(self, now):
+        return { 'timestamp'            : now,
+                 'name'                 : self.name,
+                 'writeback'            : self.stats[WB_WRITEBACK],
+                 'reclaimable'          : self.stats[WB_RECLAIMABLE],
+                 'dirtied'              : self.stats[WB_DIRTIED],
+                 'written'              : self.stats[WB_WRITTEN],
+                 'avg_wb'               : self.avg_bw, }
+
+    def table_header_str():
+        return f'{"":>16} {"writeback":>10} {"reclaimable":>12} ' \
+                f'{"dirtied":>9} {"written":>9} {"avg_bw":>9}'
+
+    def table_row_str(self):
+        out = f'{self.name[-16:]:16} ' \
+              f'{self.stats[WB_WRITEBACK]:10} ' \
+              f'{self.stats[WB_RECLAIMABLE]:12} ' \
+              f'{self.stats[WB_DIRTIED]:9} ' \
+              f'{self.stats[WB_WRITTEN]:9} ' \
+              f'{self.avg_bw:9} '
+        return out
+
+    def show_header():
+        if Stats.table_fmt:
+            print()
+            print(Stats.table_header_str())
+
+    def show_stats(self):
+        if Stats.table_fmt:
+            print(self.table_row_str())
+        else:
+            print(self.dict(Stats.now))
+
+class WbStats(Stats):
+    def __init__(self, wb):
+        bdi_name = wb.bdi.dev_name.string_().decode()
+        # avoid to use bdi.wb.memcg_css which is only defined when
+        # CONFIG_CGROUP_WRITEBACK is enabled
+        if wb == wb.bdi.wb.address_of_():
+            ino = "1"
+        else:
+            ino = str(wb.memcg_css.cgroup.kn.id.value_())
+        self.name = bdi_name + '_' + ino
+
+        self.stats = [0] * NR_WB_STAT_ITEMS
+        for i in range(NR_WB_STAT_ITEMS):
+            if wb.stat[i].count >= 0:
+                self.stats[i] = int(K(wb.stat[i].count))
+            else:
+                self.stats[i] = 0
+
+        self.avg_bw = int(K(wb.avg_write_bandwidth))
+
+class BdiStats(Stats):
+    def __init__(self, bdi):
+        self.name = bdi.dev_name.string_().decode()
+        self.stats = [0] * NR_WB_STAT_ITEMS
+        self.avg_bw = 0
+
+    def collectStats(self, wb_stats):
+        for i in range(NR_WB_STAT_ITEMS):
+            self.stats[i] += wb_stats.stats[i]
+
+        self.avg_bw += wb_stats.avg_bw
+
+exit_req = False
+
+def sigint_handler(signr, frame):
+    global exit_req
+    exit_req = True
+
+def main():
+    # handle args
+    Stats.table_fmt = not args.json
+    interval = args.interval
+    cgroup = args.cgroup
+
+    re_str = None
+    if args.bdi:
+        for r in args.bdi:
+            if re_str is None:
+                re_str = r
+            else:
+                re_str += '|' + r
+
+    filter_re = re.compile(re_str) if re_str else None
+
+    # monitoring loop
+    signal.signal(signal.SIGINT, sigint_handler)
+
+    while not exit_req:
+        Stats.now = time.time()
+
+        Stats.show_header()
+        for bdi in list_for_each_entry('struct backing_dev_info', bdi_list.address_of_(), 'bdi_list'):
+            bdi_stats = BdiStats(bdi)
+            if filter_re and not filter_re.search(bdi_stats.name):
+                continue
+
+            for wb in list_for_each_entry('struct bdi_writeback', bdi.wb_list.address_of_(), 'bdi_node'):
+                wb_stats = WbStats(wb)
+                bdi_stats.collectStats(wb_stats)
+                if cgroup:
+                    wb_stats.show_stats()
+
+            bdi_stats.show_stats()
+            if cgroup and Stats.table_fmt:
+                print()
+
+        if interval == 0:
+            break
+        time.sleep(interval)
+
+if __name__ == "__main__":
+    main()