tools/drsnoop_example.txt

Demonstrations of drsnoop, the Linux eBPF/bcc version.


drsnoop traces the direct reclaim system-wide, and prints various details.
Example output:

# ./drsnoop
COMM           PID     LAT(ms) PAGES
summond        17678      0.19   143
summond        17669      0.55   313
summond        17669      0.15   145
summond        17669      0.27   237
summond        17669      0.48   111
summond        17669      0.16    75
head           17821      0.29   339
head           17825      0.17   109
summond        17669      0.14    73
summond        17496    104.84    40
summond        17678      0.32   167
summond        17678      0.14   106
summond        17678      0.16    67
summond        17678      0.29   267
summond        17678      0.27    69
summond        17678      0.32    46
base64         17816      0.16    85
summond        17678      0.43   283
summond        17678      0.14   182
head           17736      0.57   135
^C

While tracing, the processes alloc pages，due to insufficient memory available
in the system, direct reclaim events happened, which will increase the waiting
delay of the processes.

drsnoop can be useful for discovering when allocstall(/proc/vmstat) continues to increase,
whether it is caused by some critical processes or not.

The -p option can be used to filter on a PID, which is filtered in-kernel. Here
I've used it with -T to print timestamps:

# ./drsnoop -Tp 17491
TIME(s)       COMM           PID     LAT(ms) PAGES
107.364115000 summond        17491      0.24    50
107.364550000 summond        17491      0.26    38
107.365266000 summond        17491      0.36    72
107.365753000 summond        17491      0.22    49
^C

This shows the summond process allocs pages, and direct reclaim events happening,
and the delays are not affected much.

The -U option include UID on output:

# ./drsnoop -U
UID   COMM           PID     LAT(ms) PAGES
1000  summond        17678      0.32    46
0     base64         17816      0.16    85
1000  summond        17678      0.43   283
1000  summond        17678      0.14   182
0     head           17821      0.29   339
0     head           17825      0.17   109
^C

The -u option filtering UID:

# ./drsnoop -Uu 1000
UID   COMM           PID      LAT(ms) PAGES
1000  summond        17678       0.19   143
1000  summond        17669       0.55   313
1000  summond        17669       0.15   145
1000  summond        17669       0.27   237
1000  summond        17669       0.48   111
1000  summond        17669       0.16    75
1000  summond        17669       0.14    73
1000  summond        17678       0.32   167
^C

A maximum tracing duration can be set with the -d option. For example, to trace
for 2 seconds:

# ./drsnoop -d 2
COMM           PID     LAT(ms) PAGES
head           21715      0.15   195

The -n option can be used to filter on process name using partial matches:

# ./drsnoop -n mond
COMM           PID     LAT(ms) PAGES
summond       10271       0.03    51
summond       10271       0.03    51
summond       10259       0.05    51
summond       10269     319.41    37
summond       10270     111.73    35
summond       10270       0.11    78
summond       10270       0.12    71
summond       10270       0.03    35
summond       10277     111.62    41
summond       10277       0.08    45
summond       10277       0.06    32
^C

This caught the 'summond' command because it partially matches 'mond' that's passed
to the '-n' option.


The -v option can be used to show system memory state (now only free mem) at 
the beginning of direct reclaiming:

# ./drsnoop.py -v
COMM           PID     LAT(ms) PAGES  FREE(KB)
base64         34924      0.23   151     86260
base64         34962      0.26   149     86260
head           34931      0.24   150     86260
base64         34902      0.19   148     86260
head           34963      0.19   151     86228
base64         34959      0.17   151     86228
head           34965      0.29   190     86228
base64         34957      0.24   152     86228
summond        34870      0.15   151     86080
summond        34870      0.12   115     86184

USAGE message:

# ./drsnoop -h
usage: drsnoop.py [-h] [-T] [-U] [-p PID] [-t TID] [-u UID] [-d DURATION]
                  [-n NAME]

Trace direct reclaim

optional arguments:
  -h, --help            show this help message and exit
  -T, --timestamp       include timestamp on output
  -U, --print-uid       print UID column
  -p PID, --pid PID     trace this PID only
  -t TID, --tid TID     trace this TID only
  -u UID, --uid UID     trace this UID only
  -d DURATION, --duration DURATION
                        total duration of trace in seconds
  -n NAME, --name NAME  only print process names containing this name

examples:
    ./drsnoop           # trace all direct reclaim
    ./drsnoop -T        # include timestamps
    ./drsnoop -U        # include UID
    ./drsnoop -p 181    # only trace PID 181
    ./drsnoop -t 123    # only trace TID 123
    ./drsnoop -u 1000   # only trace UID 1000
    ./drsnoop -d 10     # trace for 10 seconds only
    ./drsnoop -n main   # only print process names containing "main"