mm: count the number of partially mapped anonymous THPs per size

When a THP is added to the deferred_list due to partially mapped, its
partial pages are unused, leading to wasted memory and potentially
increasing memory reclamation pressure.

Detailing the specifics of how unmapping occurs is quite difficult and not
that useful, so we adopt a simple approach: each time a THP enters the
deferred_list, we increment the count by 1; whenever it leaves for any
reason, we decrement the count by 1.

Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: Barry Song <[email protected]>
Acked-by: David Hildenbrand <[email protected]>
Cc: Baolin Wang <[email protected]>
Cc: Chris Li <[email protected]>
Cc: Chuanhua Han <[email protected]>
Cc: Kairui Song <[email protected]>
Cc: Kalesh Singh <[email protected]>
Cc: Lance Yang <[email protected]>
Cc: Ryan Roberts <[email protected]>
Cc: Shuai Yuan <[email protected]>
Cc: Usama Arif <[email protected]>
Cc: Zi Yan <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>

1 files changed, 1 insertions, 0 deletions

diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h
index 2ee2971e4e10..4902e2f7e896 100644
--- a/include/linux/huge_mm.h
+++ b/include/linux/huge_mm.h
@@ -127,6 +127,7 @@ enum mthp_stat_item {
 	MTHP_STAT_SPLIT_FAILED,
 	MTHP_STAT_SPLIT_DEFERRED,
 	MTHP_STAT_NR_ANON,
+	MTHP_STAT_NR_ANON_PARTIALLY_MAPPED,
 	__MTHP_STAT_COUNT
 };