1.. _shrinker_debugfs:
2
3==========================
4Shrinker Debugfs Interface
5==========================
6
7Shrinker debugfs interface provides a visibility into the kernel memory
8shrinkers subsystem and allows to get information about individual shrinkers
9and interact with them.
10
11For each shrinker registered in the system a directory in **<debugfs>/shrinker/**
12is created. The directory's name is composed from the shrinker's name and an
13unique id: e.g. *kfree_rcu-0* or *sb-xfs:vda1-36*.
14
15Each shrinker directory contains **count** and **scan** files, which allow to
16trigger *count_objects()* and *scan_objects()* callbacks for each memcg and
17numa node (if applicable).
18
19Usage:
20------
21
221. *List registered shrinkers*
23
24  ::
25
26    $ cd /sys/kernel/debug/shrinker/
27    $ ls
28    dquota-cache-16     sb-devpts-28     sb-proc-47       sb-tmpfs-42
29    mm-shadow-18        sb-devtmpfs-5    sb-proc-48       sb-tmpfs-43
30    mm-zspool:zram0-34  sb-hugetlbfs-17  sb-pstore-31     sb-tmpfs-44
31    rcu-kfree-0         sb-hugetlbfs-33  sb-rootfs-2      sb-tmpfs-49
32    sb-aio-20           sb-iomem-12      sb-securityfs-6  sb-tracefs-13
33    sb-anon_inodefs-15  sb-mqueue-21     sb-selinuxfs-22  sb-xfs:vda1-36
34    sb-bdev-3           sb-nsfs-4        sb-sockfs-8      sb-zsmalloc-19
35    sb-bpf-32           sb-pipefs-14     sb-sysfs-26      thp-deferred_split-10
36    sb-btrfs:vda2-24    sb-proc-25       sb-tmpfs-1       thp-zero-9
37    sb-cgroup2-30       sb-proc-39       sb-tmpfs-27      xfs-buf:vda1-37
38    sb-configfs-23      sb-proc-41       sb-tmpfs-29      xfs-inodegc:vda1-38
39    sb-dax-11           sb-proc-45       sb-tmpfs-35
40    sb-debugfs-7        sb-proc-46       sb-tmpfs-40
41
422. *Get information about a specific shrinker*
43
44  ::
45
46    $ cd sb-btrfs\:vda2-24/
47    $ ls
48    count            scan
49
503. *Count objects*
51
52  Each line in the output has the following format::
53
54    <cgroup inode id> <nr of objects on node 0> <nr of objects on node 1> ...
55    <cgroup inode id> <nr of objects on node 0> <nr of objects on node 1> ...
56    ...
57
58  If there are no objects on all numa nodes, a line is omitted. If there
59  are no objects at all, the output might be empty.
60
61  If the shrinker is not memcg-aware or CONFIG_MEMCG is off, 0 is printed
62  as cgroup inode id. If the shrinker is not numa-aware, 0's are printed
63  for all nodes except the first one.
64  ::
65
66    $ cat count
67    1 224 2
68    21 98 0
69    55 818 10
70    2367 2 0
71    2401 30 0
72    225 13 0
73    599 35 0
74    939 124 0
75    1041 3 0
76    1075 1 0
77    1109 1 0
78    1279 60 0
79    1313 7 0
80    1347 39 0
81    1381 3 0
82    1449 14 0
83    1483 63 0
84    1517 53 0
85    1551 6 0
86    1585 1 0
87    1619 6 0
88    1653 40 0
89    1687 11 0
90    1721 8 0
91    1755 4 0
92    1789 52 0
93    1823 888 0
94    1857 1 0
95    1925 2 0
96    1959 32 0
97    2027 22 0
98    2061 9 0
99    2469 799 0
100    2537 861 0
101    2639 1 0
102    2707 70 0
103    2775 4 0
104    2877 84 0
105    293 1 0
106    735 8 0
107
1084. *Scan objects*
109
110  The expected input format::
111
112    <cgroup inode id> <numa id> <number of objects to scan>
113
114  For a non-memcg-aware shrinker or on a system with no memory
115  cgrups **0** should be passed as cgroup id.
116  ::
117
118    $ cd /sys/kernel/debug/shrinker/
119    $ cd sb-btrfs\:vda2-24/
120
121    $ cat count | head -n 5
122    1 212 0
123    21 97 0
124    55 802 5
125    2367 2 0
126    225 13 0
127
128    $ echo "55 0 200" > scan
129
130    $ cat count | head -n 5
131    1 212 0
132    21 96 0
133    55 752 5
134    2367 2 0
135    225 13 0
136