1==========================
2Shrinker Debugfs Interface
3==========================
4
5Shrinker debugfs interface provides a visibility into the kernel memory
6shrinkers subsystem and allows to get information about individual shrinkers
7and interact with them.
8
9For each shrinker registered in the system a directory in **<debugfs>/shrinker/**
10is created. The directory's name is composed from the shrinker's name and an
11unique id: e.g. *kfree_rcu-0* or *sb-xfs:vda1-36*.
12
13Each shrinker directory contains **count** and **scan** files, which allow to
14trigger *count_objects()* and *scan_objects()* callbacks for each memcg and
15numa node (if applicable).
16
17Usage:
18------
19
201. *List registered shrinkers*
21
22  ::
23
24    $ cd /sys/kernel/debug/shrinker/
25    $ ls
26    dquota-cache-16     sb-devpts-28     sb-proc-47       sb-tmpfs-42
27    mm-shadow-18        sb-devtmpfs-5    sb-proc-48       sb-tmpfs-43
28    mm-zspool:zram0-34  sb-hugetlbfs-17  sb-pstore-31     sb-tmpfs-44
29    rcu-kfree-0         sb-hugetlbfs-33  sb-rootfs-2      sb-tmpfs-49
30    sb-aio-20           sb-iomem-12      sb-securityfs-6  sb-tracefs-13
31    sb-anon_inodefs-15  sb-mqueue-21     sb-selinuxfs-22  sb-xfs:vda1-36
32    sb-bdev-3           sb-nsfs-4        sb-sockfs-8      sb-zsmalloc-19
33    sb-bpf-32           sb-pipefs-14     sb-sysfs-26      thp-deferred_split-10
34    sb-btrfs:vda2-24    sb-proc-25       sb-tmpfs-1       thp-zero-9
35    sb-cgroup2-30       sb-proc-39       sb-tmpfs-27      xfs-buf:vda1-37
36    sb-configfs-23      sb-proc-41       sb-tmpfs-29      xfs-inodegc:vda1-38
37    sb-dax-11           sb-proc-45       sb-tmpfs-35
38    sb-debugfs-7        sb-proc-46       sb-tmpfs-40
39
402. *Get information about a specific shrinker*
41
42  ::
43
44    $ cd sb-btrfs\:vda2-24/
45    $ ls
46    count            scan
47
483. *Count objects*
49
50  Each line in the output has the following format::
51
52    <cgroup inode id> <nr of objects on node 0> <nr of objects on node 1> ...
53    <cgroup inode id> <nr of objects on node 0> <nr of objects on node 1> ...
54    ...
55
56  If there are no objects on all numa nodes, a line is omitted. If there
57  are no objects at all, the output might be empty.
58
59  If the shrinker is not memcg-aware or CONFIG_MEMCG is off, 0 is printed
60  as cgroup inode id. If the shrinker is not numa-aware, 0's are printed
61  for all nodes except the first one.
62  ::
63
64    $ cat count
65    1 224 2
66    21 98 0
67    55 818 10
68    2367 2 0
69    2401 30 0
70    225 13 0
71    599 35 0
72    939 124 0
73    1041 3 0
74    1075 1 0
75    1109 1 0
76    1279 60 0
77    1313 7 0
78    1347 39 0
79    1381 3 0
80    1449 14 0
81    1483 63 0
82    1517 53 0
83    1551 6 0
84    1585 1 0
85    1619 6 0
86    1653 40 0
87    1687 11 0
88    1721 8 0
89    1755 4 0
90    1789 52 0
91    1823 888 0
92    1857 1 0
93    1925 2 0
94    1959 32 0
95    2027 22 0
96    2061 9 0
97    2469 799 0
98    2537 861 0
99    2639 1 0
100    2707 70 0
101    2775 4 0
102    2877 84 0
103    293 1 0
104    735 8 0
105
1064. *Scan objects*
107
108  The expected input format::
109
110    <cgroup inode id> <numa id> <number of objects to scan>
111
112  For a non-memcg-aware shrinker or on a system with no memory
113  cgrups **0** should be passed as cgroup id.
114  ::
115
116    $ cd /sys/kernel/debug/shrinker/
117    $ cd sb-btrfs\:vda2-24/
118
119    $ cat count | head -n 5
120    1 212 0
121    21 97 0
122    55 802 5
123    2367 2 0
124    225 13 0
125
126    $ echo "55 0 200" > scan
127
128    $ cat count | head -n 5
129    1 212 0
130    21 96 0
131    55 752 5
132    2367 2 0
133    225 13 0
134