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

From: Lance Yang
Date: Fri Jun 28 2024 - 09:09:35 EST


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

Signed-off-by: Mingzhe Yang <mingzhe.yang@xxxxxx>
Signed-off-by: Lance Yang <ioworker0@xxxxxxxxx>
---
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