0001 .. _shrinker_debugfs:
0002
0003 ==========================
0004 Shrinker Debugfs Interface
0005 ==========================
0006
0007 Shrinker debugfs interface provides a visibility into the kernel memory
0008 shrinkers subsystem and allows to get information about individual shrinkers
0009 and interact with them.
0010
0011 For each shrinker registered in the system a directory in **<debugfs>/shrinker/**
0012 is created. The directory's name is composed from the shrinker's name and an
0013 unique id: e.g. *kfree_rcu-0* or *sb-xfs:vda1-36*.
0014
0015 Each shrinker directory contains **count** and **scan** files, which allow to
0016 trigger *count_objects()* and *scan_objects()* callbacks for each memcg and
0017 numa node (if applicable).
0018
0019 Usage:
0020 ------
0021
0022 1. *List registered shrinkers*
0023
0024 ::
0025
0026 $ cd /sys/kernel/debug/shrinker/
0027 $ ls
0028 dquota-cache-16 sb-devpts-28 sb-proc-47 sb-tmpfs-42
0029 mm-shadow-18 sb-devtmpfs-5 sb-proc-48 sb-tmpfs-43
0030 mm-zspool:zram0-34 sb-hugetlbfs-17 sb-pstore-31 sb-tmpfs-44
0031 rcu-kfree-0 sb-hugetlbfs-33 sb-rootfs-2 sb-tmpfs-49
0032 sb-aio-20 sb-iomem-12 sb-securityfs-6 sb-tracefs-13
0033 sb-anon_inodefs-15 sb-mqueue-21 sb-selinuxfs-22 sb-xfs:vda1-36
0034 sb-bdev-3 sb-nsfs-4 sb-sockfs-8 sb-zsmalloc-19
0035 sb-bpf-32 sb-pipefs-14 sb-sysfs-26 thp-deferred_split-10
0036 sb-btrfs:vda2-24 sb-proc-25 sb-tmpfs-1 thp-zero-9
0037 sb-cgroup2-30 sb-proc-39 sb-tmpfs-27 xfs-buf:vda1-37
0038 sb-configfs-23 sb-proc-41 sb-tmpfs-29 xfs-inodegc:vda1-38
0039 sb-dax-11 sb-proc-45 sb-tmpfs-35
0040 sb-debugfs-7 sb-proc-46 sb-tmpfs-40
0041
0042 2. *Get information about a specific shrinker*
0043
0044 ::
0045
0046 $ cd sb-btrfs\:vda2-24/
0047 $ ls
0048 count scan
0049
0050 3. *Count objects*
0051
0052 Each line in the output has the following format::
0053
0054 <cgroup inode id> <nr of objects on node 0> <nr of objects on node 1> ...
0055 <cgroup inode id> <nr of objects on node 0> <nr of objects on node 1> ...
0056 ...
0057
0058 If there are no objects on all numa nodes, a line is omitted. If there
0059 are no objects at all, the output might be empty.
0060
0061 If the shrinker is not memcg-aware or CONFIG_MEMCG is off, 0 is printed
0062 as cgroup inode id. If the shrinker is not numa-aware, 0's are printed
0063 for all nodes except the first one.
0064 ::
0065
0066 $ cat count
0067 1 224 2
0068 21 98 0
0069 55 818 10
0070 2367 2 0
0071 2401 30 0
0072 225 13 0
0073 599 35 0
0074 939 124 0
0075 1041 3 0
0076 1075 1 0
0077 1109 1 0
0078 1279 60 0
0079 1313 7 0
0080 1347 39 0
0081 1381 3 0
0082 1449 14 0
0083 1483 63 0
0084 1517 53 0
0085 1551 6 0
0086 1585 1 0
0087 1619 6 0
0088 1653 40 0
0089 1687 11 0
0090 1721 8 0
0091 1755 4 0
0092 1789 52 0
0093 1823 888 0
0094 1857 1 0
0095 1925 2 0
0096 1959 32 0
0097 2027 22 0
0098 2061 9 0
0099 2469 799 0
0100 2537 861 0
0101 2639 1 0
0102 2707 70 0
0103 2775 4 0
0104 2877 84 0
0105 293 1 0
0106 735 8 0
0107
0108 4. *Scan objects*
0109
0110 The expected input format::
0111
0112 <cgroup inode id> <numa id> <number of objects to scan>
0113
0114 For a non-memcg-aware shrinker or on a system with no memory
0115 cgrups **0** should be passed as cgroup id.
0116 ::
0117
0118 $ cd /sys/kernel/debug/shrinker/
0119 $ cd sb-btrfs\:vda2-24/
0120
0121 $ cat count | head -n 5
0122 1 212 0
0123 21 97 0
0124 55 802 5
0125 2367 2 0
0126 225 13 0
0127
0128 $ echo "55 0 200" > scan
0129
0130 $ cat count | head -n 5
0131 1 212 0
0132 21 96 0
0133 55 752 5
0134 2367 2 0
0135 225 13 0
