Add a document describing the shrinker debugfs interface.
Signed-off-by: Roman Gushchin <roman.gushchin@xxxxxxxxx>
---
Documentation/admin-guide/mm/index.rst | 1 +
.../admin-guide/mm/shrinker_debugfs.rst | 90 +++++++++++++++++++
2 files changed, 91 insertions(+)
create mode 100644 Documentation/admin-guide/mm/shrinker_debugfs.rst
diff --git a/Documentation/admin-guide/mm/index.rst b/Documentation/admin-guide/mm/index.rst
index c21b5823f126..1bd11118dfb1 100644
--- a/Documentation/admin-guide/mm/index.rst
+++ b/Documentation/admin-guide/mm/index.rst
@@ -36,6 +36,7 @@ the Linux memory management.
numa_memory_policy
numaperf
pagemap
+ shrinker_debugfs
soft-dirty
swap_numa
transhuge
diff --git a/Documentation/admin-guide/mm/shrinker_debugfs.rst b/Documentation/admin-guide/mm/shrinker_debugfs.rst
new file mode 100644
index 000000000000..c2f3da534b70
--- /dev/null
+++ b/Documentation/admin-guide/mm/shrinker_debugfs.rst
@@ -0,0 +1,90 @@
+==========================
+Shrinker Debugfs Interface
+==========================
+
+Shrinker debugfs interface provides a visibility into the kernel memory
+shrinkers subsystem and allows to get statistics and interact with
+individual shrinkers.
+
+For each shrinker registered in the system a directory in <debugfs>/shrinker/
+is created. The directory is named like "kfree_rcu-0". Each name is composed
+from the shrinker's name and an unique id.
+
+Each shrinker directory contains "count" and "scan" files, which allow
+to trigger count_objects() and scan_objects() callbacks. For memcg-aware
+and numa-aware shrinkers count_memcg, scan_memcg, count_node, scan_node,
+count_memcg_node and scan_memcg_node are additionally provided. They allow
+to get per-memcg and/or per-node object count and shrink only a specific
+memcg/node.
+
+Usage examples:
+
+ 1. List registered shrinkers::
+ $ cd /sys/kernel/debug/shrinker/
+ $ ls
+ dqcache-16 sb-cgroup2-30 sb-hugetlbfs-33 sb-proc-41 sb-selinuxfs-22 sb-tmpfs-40 sb-zsmalloc-19
+ kfree_rcu-0 sb-configfs-23 sb-iomem-12 sb-proc-44 sb-sockfs-8 sb-tmpfs-42 shadow-18
+ sb-aio-20 sb-dax-11 sb-mqueue-21 sb-proc-45 sb-sysfs-26 sb-tmpfs-43 thp_deferred_split-10
+ sb-anon_inodefs-15 sb-debugfs-7 sb-nsfs-4 sb-proc-47 sb-tmpfs-1 sb-tmpfs-46 thp_zero-9
+ sb-bdev-3 sb-devpts-28 sb-pipefs-14 sb-pstore-31 sb-tmpfs-27 sb-tmpfs-49 xfs_buf-37
+ sb-bpf-32 sb-devtmpfs-5 sb-proc-25 sb-rootfs-2 sb-tmpfs-29 sb-tracefs-13 xfs_inodegc-38
+ sb-btrfs-24 sb-hugetlbfs-17 sb-proc-39 sb-securityfs-6 sb-tmpfs-35 sb-xfs-36 zspool-34
+
+ 2. Get information about a specific shrinker::
+ $ cd sb-btrfs-24/
+ $ ls
+ count count_memcg count_memcg_node count_node scan scan_memcg scan_memcg_node scan_node
+
+ 3. Count objects on the system/root cgroup level::
+ $ cat count
+ 212
+
+ 4. Count objects on the system/root cgroup level per numa node (on a 2-node machine)::
+ $ cat count_node
+ 209 3
+
+ 5. Count objects for each memcg (output format: cgroup inode, count)::
+ $ cat count_memcg
+ 1 212
+ 20 96
+ 53 817
+ 2297 2
+ 218 13
+ 581 30
+ 911 124
+ ...
+
+ 6. Same but with a per-node output::
+ $ cat count_memcg_node
+ 1 209 3
+ 20 96 0
+ 53 810 7
+ 2297 2 0
+ 218 13 0
+ 581 30 0
+ 911 124 0
+ ...
+
+ 7. Scan system/root shrinker::
+ $ cat count
+ 212
+ $ echo 100 > scan
+ $ cat scan
+ 97
+ $ cat count
+ 115
+
+ 8. Scan individual memcg::
+ $ echo "1868 500" > scan_memcg
+ $ cat scan_memcg
+ 193
+
+ 9. Scan individual node::
+ $ echo "1 200" > scan_node
+ $ cat scan_node
+ 2
+
+ 10. Scan individual memcg and node::
+ $ echo "1868 0 500" > scan_memcg_node
+ $ cat scan_memcg_node
+ 435
--
2.35.1
