[PATCH v2 2/2] mm: add docs for per-order mTHP split counters

[Lance Yang <ioworker0@gmail.com>]

This commit introduces documentation for mTHP split counters in
transhuge.rst.

Signed-off-by: Mingzhe Yang <mingzhe.yang@ly.com>
Signed-off-by: Lance Yang <ioworker0@gmail.com>
---
 Documentation/admin-guide/mm/transhuge.rst | 16 ++++++++++++++++
 1 file changed, 16 insertions(+)

diff --git a/Documentation/admin-guide/mm/transhuge.rst b/Documentation/admin-guide/mm/transhuge.rst
index 1f72b00af5d3..709fe10b60f4 100644
--- a/Documentation/admin-guide/mm/transhuge.rst
+++ b/Documentation/admin-guide/mm/transhuge.rst
@@ -514,6 +514,22 @@ file_fallback_charge
 	falls back to using small pages even though the allocation was
 	successful.
 
+split
+	is incremented every time a huge page is successfully split into
+	base pages. This can happen for a variety of reasons but a common
+	reason is that a huge page is old and is being reclaimed.
+	This action implies splitting any block mappings into PTEs.
+
+split_failed
+	is incremented if kernel fails to split huge
+	page. This can happen if the page was pinned by somebody.
+
+split_deferred
+	is incremented when a huge page is put onto split
+	queue. This happens when a huge page is partially unmapped and
+	splitting it would free up some memory. Pages on split queue are
+	going to be split under memory pressure.
+
 As the system ages, allocating huge pages may be expensive as the
 system uses memory compaction to copy data around memory to free a
 huge page for use. There are some counters in ``/proc/vmstat`` to help
-- 
2.45.2