1 ========================== 1 ==========================
2 Shrinker Debugfs Interface 2 Shrinker Debugfs Interface
3 ========================== 3 ==========================
4 4
5 Shrinker debugfs interface provides a visibili 5 Shrinker debugfs interface provides a visibility into the kernel memory
6 shrinkers subsystem and allows to get informat 6 shrinkers subsystem and allows to get information about individual shrinkers
7 and interact with them. 7 and interact with them.
8 8
9 For each shrinker registered in the system a d 9 For each shrinker registered in the system a directory in **<debugfs>/shrinker/**
10 is created. The directory's name is composed f 10 is created. The directory's name is composed from the shrinker's name and an
11 unique id: e.g. *kfree_rcu-0* or *sb-xfs:vda1- 11 unique id: e.g. *kfree_rcu-0* or *sb-xfs:vda1-36*.
12 12
13 Each shrinker directory contains **count** and 13 Each shrinker directory contains **count** and **scan** files, which allow to
14 trigger *count_objects()* and *scan_objects()* 14 trigger *count_objects()* and *scan_objects()* callbacks for each memcg and
15 numa node (if applicable). 15 numa node (if applicable).
16 16
17 Usage: 17 Usage:
18 ------ 18 ------
19 19
20 1. *List registered shrinkers* 20 1. *List registered shrinkers*
21 21
22 :: 22 ::
23 23
24 $ cd /sys/kernel/debug/shrinker/ 24 $ cd /sys/kernel/debug/shrinker/
25 $ ls 25 $ ls
26 dquota-cache-16 sb-devpts-28 sb-pr 26 dquota-cache-16 sb-devpts-28 sb-proc-47 sb-tmpfs-42
27 mm-shadow-18 sb-devtmpfs-5 sb-pr 27 mm-shadow-18 sb-devtmpfs-5 sb-proc-48 sb-tmpfs-43
28 mm-zspool:zram0-34 sb-hugetlbfs-17 sb-ps 28 mm-zspool:zram0-34 sb-hugetlbfs-17 sb-pstore-31 sb-tmpfs-44
29 rcu-kfree-0 sb-hugetlbfs-33 sb-ro 29 rcu-kfree-0 sb-hugetlbfs-33 sb-rootfs-2 sb-tmpfs-49
30 sb-aio-20 sb-iomem-12 sb-se 30 sb-aio-20 sb-iomem-12 sb-securityfs-6 sb-tracefs-13
31 sb-anon_inodefs-15 sb-mqueue-21 sb-se 31 sb-anon_inodefs-15 sb-mqueue-21 sb-selinuxfs-22 sb-xfs:vda1-36
32 sb-bdev-3 sb-nsfs-4 sb-so 32 sb-bdev-3 sb-nsfs-4 sb-sockfs-8 sb-zsmalloc-19
33 sb-bpf-32 sb-pipefs-14 sb-sy 33 sb-bpf-32 sb-pipefs-14 sb-sysfs-26 thp-deferred_split-10
34 sb-btrfs:vda2-24 sb-proc-25 sb-tm 34 sb-btrfs:vda2-24 sb-proc-25 sb-tmpfs-1 thp-zero-9
35 sb-cgroup2-30 sb-proc-39 sb-tm 35 sb-cgroup2-30 sb-proc-39 sb-tmpfs-27 xfs-buf:vda1-37
36 sb-configfs-23 sb-proc-41 sb-tm 36 sb-configfs-23 sb-proc-41 sb-tmpfs-29 xfs-inodegc:vda1-38
37 sb-dax-11 sb-proc-45 sb-tm 37 sb-dax-11 sb-proc-45 sb-tmpfs-35
38 sb-debugfs-7 sb-proc-46 sb-tm 38 sb-debugfs-7 sb-proc-46 sb-tmpfs-40
39 39
40 2. *Get information about a specific shrinker* 40 2. *Get information about a specific shrinker*
41 41
42 :: 42 ::
43 43
44 $ cd sb-btrfs\:vda2-24/ 44 $ cd sb-btrfs\:vda2-24/
45 $ ls 45 $ ls
46 count scan 46 count scan
47 47
48 3. *Count objects* 48 3. *Count objects*
49 49
50 Each line in the output has the following fo 50 Each line in the output has the following format::
51 51
52 <cgroup inode id> <nr of objects on node 0 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 53 <cgroup inode id> <nr of objects on node 0> <nr of objects on node 1> ...
54 ... 54 ...
55 55
56 If there are no objects on all numa nodes, a 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 e 57 are no objects at all, the output might be empty.
58 58
59 If the shrinker is not memcg-aware or CONFIG 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 n 60 as cgroup inode id. If the shrinker is not numa-aware, 0's are printed
61 for all nodes except the first one. 61 for all nodes except the first one.
62 :: 62 ::
63 63
64 $ cat count 64 $ cat count
65 1 224 2 65 1 224 2
66 21 98 0 66 21 98 0
67 55 818 10 67 55 818 10
68 2367 2 0 68 2367 2 0
69 2401 30 0 69 2401 30 0
70 225 13 0 70 225 13 0
71 599 35 0 71 599 35 0
72 939 124 0 72 939 124 0
73 1041 3 0 73 1041 3 0
74 1075 1 0 74 1075 1 0
75 1109 1 0 75 1109 1 0
76 1279 60 0 76 1279 60 0
77 1313 7 0 77 1313 7 0
78 1347 39 0 78 1347 39 0
79 1381 3 0 79 1381 3 0
80 1449 14 0 80 1449 14 0
81 1483 63 0 81 1483 63 0
82 1517 53 0 82 1517 53 0
83 1551 6 0 83 1551 6 0
84 1585 1 0 84 1585 1 0
85 1619 6 0 85 1619 6 0
86 1653 40 0 86 1653 40 0
87 1687 11 0 87 1687 11 0
88 1721 8 0 88 1721 8 0
89 1755 4 0 89 1755 4 0
90 1789 52 0 90 1789 52 0
91 1823 888 0 91 1823 888 0
92 1857 1 0 92 1857 1 0
93 1925 2 0 93 1925 2 0
94 1959 32 0 94 1959 32 0
95 2027 22 0 95 2027 22 0
96 2061 9 0 96 2061 9 0
97 2469 799 0 97 2469 799 0
98 2537 861 0 98 2537 861 0
99 2639 1 0 99 2639 1 0
100 2707 70 0 100 2707 70 0
101 2775 4 0 101 2775 4 0
102 2877 84 0 102 2877 84 0
103 293 1 0 103 293 1 0
104 735 8 0 104 735 8 0
105 105
106 4. *Scan objects* 106 4. *Scan objects*
107 107
108 The expected input format:: 108 The expected input format::
109 109
110 <cgroup inode id> <numa id> <number of obj 110 <cgroup inode id> <numa id> <number of objects to scan>
111 111
112 For a non-memcg-aware shrinker or on a syste 112 For a non-memcg-aware shrinker or on a system with no memory
113 cgrups **0** should be passed as cgroup id. 113 cgrups **0** should be passed as cgroup id.
114 :: 114 ::
115 115
116 $ cd /sys/kernel/debug/shrinker/ 116 $ cd /sys/kernel/debug/shrinker/
117 $ cd sb-btrfs\:vda2-24/ 117 $ cd sb-btrfs\:vda2-24/
118 118
119 $ cat count | head -n 5 119 $ cat count | head -n 5
120 1 212 0 120 1 212 0
121 21 97 0 121 21 97 0
122 55 802 5 122 55 802 5
123 2367 2 0 123 2367 2 0
124 225 13 0 124 225 13 0
125 125
126 $ echo "55 0 200" > scan 126 $ echo "55 0 200" > scan
127 127
128 $ cat count | head -n 5 128 $ cat count | head -n 5
129 1 212 0 129 1 212 0
130 21 96 0 130 21 96 0
131 55 752 5 131 55 752 5
132 2367 2 0 132 2367 2 0
133 225 13 0 133 225 13 0
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