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SubjectRe: [PATCH v4 4/6] mm: docs: document shrinker debugfs
On Wed, May 25, 2022 at 01:25:58PM -0700, Roman Gushchin wrote:
> Add a document describing the shrinker debugfs interface.
>
> Signed-off-by: Roman Gushchin <roman.gushchin@linux.dev>
> ---
> Documentation/admin-guide/mm/index.rst | 1 +
> .../admin-guide/mm/shrinker_debugfs.rst | 100 ++++++++++++++++++
> 2 files changed, 101 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..2033d696aa59
> --- /dev/null
> +++ b/Documentation/admin-guide/mm/shrinker_debugfs.rst
> @@ -0,0 +1,100 @@
> +.. _shrinker_debugfs:
> +
> +==========================
> +Shrinker Debugfs Interface
> +==========================
> +
> +Shrinker debugfs interface provides a visibility into the kernel memory
> +shrinkers subsystem and allows to get information about individual shrinkers.
> +
> +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 the **count** file, which allows to trigger
> +the *count_objects()* callback for each memcg and numa node (if applicable).
> +
> +Usage:
> +------
> +
> +1. *List registered shrinkers*
> +
> + ::
> +
> + $ cd /sys/kernel/debug/shrinker/
> + $ ls
> + dqcache-16 sb-hugetlbfs-17 sb-rootfs-2 sb-tmpfs-49
> + kfree_rcu-0 sb-hugetlbfs-33 sb-securityfs-6 sb-tracefs-13
> + sb-aio-20 sb-iomem-12 sb-selinuxfs-22 sb-xfs:vda1-36
> + sb-anon_inodefs-15 sb-mqueue-21 sb-sockfs-8 sb-zsmalloc-19
> + sb-bdev-3 sb-nsfs-4 sb-sysfs-26 shadow-18
> + sb-bpf-32 sb-pipefs-14 sb-tmpfs-1 thp_deferred_split-10
> + sb-btrfs:vda2-24 sb-proc-25 sb-tmpfs-27 thp_zero-9
> + sb-cgroup2-30 sb-proc-39 sb-tmpfs-29 xfs_buf-vda1-37
> + sb-configfs-23 sb-proc-41 sb-tmpfs-35 xfs_inodegc-vda1-38
> + sb-dax-11 sb-proc-45 sb-tmpfs-40 zspool-zram0-34
> + sb-debugfs-7 sb-proc-46 sb-tmpfs-42
> + sb-devpts-28 sb-proc-47 sb-tmpfs-43
> + sb-devtmpfs-5 sb-pstore-31 sb-tmpfs-44
> +
> +2. *Get information about a specific shrinker*
> +
> + ::
> +
> + $ cd sb-btrfs\:vda2-24/
> + $ ls
> + count
> +
> +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.

Should we add the following lines into here?

"
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.
"

Thanks.

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