Linux kernel mirror (for testing)
git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
tjh.dev
kernel
os
linux
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