==========================Shrinker Debugfs Interface========================== Shrinker debugfs interface provides a visibility into the kernel memoryshrinkers subsystem and allows to get information about individual shrinkersand interact with them. For each shrinker registered in the system a directory in **<debugfs>/shrinker/**is created. The directory's name is composed from the shrinker's name and anunique id: e.g. *kfree_rcu-0* or *sb-xfs:vda1-36*. Each shrinker directory contains **count** and **scan** files, which allow totrigger *count_objects()* and *scan_objects()* callbacks for each memcg andnuma node (if applicable). Usage:------ 1. *List registered shrinkers*   ::     $ cd /sys/kernel/debug/shrinker/    $ ls    dquota-cache-16     sb-devpts-28     sb-proc-47       sb-tmpfs-42    mm-shadow-18        sb-devtmpfs-5    sb-proc-48       sb-tmpfs-43    mm-zspool:zram0-34  sb-hugetlbfs-17  sb-pstore-31     sb-tmpfs-44    rcu-kfree-0         sb-hugetlbfs-33  sb-rootfs-2      sb-tmpfs-49    sb-aio-20           sb-iomem-12      sb-securityfs-6  sb-tracefs-13    sb-anon_inodefs-15  sb-mqueue-21     sb-selinuxfs-22  sb-xfs:vda1-36    sb-bdev-3           sb-nsfs-4        sb-sockfs-8      sb-zsmalloc-19    sb-bpf-32           sb-pipefs-14     sb-sysfs-26      thp-deferred_split-10    sb-btrfs:vda2-24    sb-proc-25       sb-tmpfs-1       thp-zero-9    sb-cgroup2-30       sb-proc-39       sb-tmpfs-27      xfs-buf:vda1-37    sb-configfs-23      sb-proc-41       sb-tmpfs-29      xfs-inodegc:vda1-38    sb-dax-11           sb-proc-45       sb-tmpfs-35    sb-debugfs-7        sb-proc-46       sb-tmpfs-40 2. *Get information about a specific shrinker*   ::     $ cd sb-btrfs\:vda2-24/    $ ls    count            scan 3. *Count objects*   Each line in the output has the following format::     <cgroup inode id> <nr of objects on node 0> <nr of objects on node 1> ...    <cgroup inode id> <nr of objects on node 0> <nr of objects on node 1> ...    ...   If there are no objects on all numa nodes, a line is omitted. If there  are no objects at all, the output might be empty.   If the shrinker is not memcg-aware or CONFIG_MEMCG is off, 0 is printed  as cgroup inode id. If the shrinker is not numa-aware, 0's are printed  for all nodes except the first one.  ::     $ cat count    1 224 2    21 98 0    55 818 10    2367 2 0    2401 30 0    225 13 0    599 35 0    939 124 0    1041 3 0    1075 1 0    1109 1 0    1279 60 0    1313 7 0    1347 39 0    1381 3 0    1449 14 0    1483 63 0    1517 53 0    1551 6 0    1585 1 0    1619 6 0    1653 40 0    1687 11 0    1721 8 0    1755 4 0    1789 52 0    1823 888 0    1857 1 0    1925 2 0    1959 32 0    2027 22 0    2061 9 0    2469 799 0    2537 861 0    2639 1 0    2707 70 0    2775 4 0    2877 84 0    293 1 0    735 8 0 4. *Scan objects*   The expected input format::     <cgroup inode id> <numa id> <number of objects to scan>   For a non-memcg-aware shrinker or on a system with no memory  cgrups **0** should be passed as cgroup id.  ::     $ cd /sys/kernel/debug/shrinker/    $ cd sb-btrfs\:vda2-24/     $ cat count | head -n 5    1 212 0    21 97 0    55 802 5    2367 2 0    225 13 0     $ echo "55 0 200" > scan     $ cat count | head -n 5    1 212 0    21 96 0    55 752 5    2367 2 0    225 13 0