Shrinker Debugfs Interface¶
Shrinker debugfs interface provides a visibility into the kernel memory shrinkers subsystem and allows to get information about individual shrinkers and 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 an unique id: e.g. kfree_rcu-0 or sb-xfs:vda1-36.
Each shrinker directory contains count and scan files, which allow to trigger count_objects() and scan_objects() callbacks for each memcg and numa node (if applicable).
Usage:¶
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
Get information about a specific shrinker
$ cd sb-btrfs\:vda2-24/ $ ls count scan
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
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