[PATCH v3 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.

Reviewed-by: Barry Song <baohua@kernel.org>
Signed-off-by: Mingzhe Yang <mingzhe.yang@ly.com>
Signed-off-by: Lance Yang <ioworker0@gmail.com>
---
 Documentation/admin-guide/mm/transhuge.rst | 20 ++++++++++++++++----
 1 file changed, 16 insertions(+), 4 deletions(-)

diff --git a/Documentation/admin-guide/mm/transhuge.rst b/Documentation/admin-guide/mm/transhuge.rst
index 1f72b00af5d3..0830aa173a8b 100644
--- a/Documentation/admin-guide/mm/transhuge.rst
+++ b/Documentation/admin-guide/mm/transhuge.rst
@@ -369,10 +369,6 @@ also applies to the regions registered in khugepaged.
 Monitoring usage
 ================
 
-.. note::
-   Currently the below counters only record events relating to
-   PMD-sized THP. Events relating to other THP sizes are not included.
-
 The number of PMD-sized anonymous transparent huge pages currently used by the
 system is available by reading the AnonHugePages field in ``/proc/meminfo``.
 To identify what applications are using PMD-sized anonymous transparent huge
@@ -514,6 +510,22 @@ 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
+	smaller orders. 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