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