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1 | ========================== |
2 | Shrinker Debugfs Interface | |
3 | ========================== | |
4 | ||
5 | Shrinker debugfs interface provides a visibility into the kernel memory | |
bbf535fd RG |
6 | shrinkers subsystem and allows to get information about individual shrinkers |
7 | and interact with them. | |
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8 | |
9 | For each shrinker registered in the system a directory in **<debugfs>/shrinker/** | |
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:vda1-36*. | |
12 | ||
bbf535fd RG |
13 | Each shrinker directory contains **count** and **scan** files, which allow to |
14 | trigger *count_objects()* and *scan_objects()* callbacks for each memcg and | |
15 | numa node (if applicable). | |
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16 | |
17 | Usage: | |
18 | ------ | |
19 | ||
20 | 1. *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 | ||
40 | 2. *Get information about a specific shrinker* | |
41 | ||
42 | :: | |
43 | ||
44 | $ cd sb-btrfs\:vda2-24/ | |
45 | $ ls | |
bbf535fd | 46 | count scan |
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47 | |
48 | 3. *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 | |
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105 | |
106 | 4. *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 |