[PATCH -mm -v2 12/12] mm, THP, swap: Add THP swapping out fallback counting

[Huang, Ying]

From: Huang Ying <ying.huang@xxxxxxxxx>

When swapping out THP (Transparent Huge Page), instead of swapping out
the THP as a whole, sometimes we have to fallback to split the THP
into normal pages before swapping, because no free swap clusters are
available, or cgroup limit is exceeded, etc.  To count the number of
the fallback, a new VM event THP_SWPOUT_FALLBACK is added, and counted
when we fallback to split the THP.

Signed-off-by: "Huang, Ying" <ying.huang@xxxxxxxxx>
Cc: Johannes Weiner <hannes@xxxxxxxxxxx>
Cc: Minchan Kim <minchan@xxxxxxxxxx>
Cc: Hugh Dickins <hughd@xxxxxxxxxx>
Cc: Shaohua Li <shli@xxxxxxxxxx>
Cc: Rik van Riel <riel@xxxxxxxxxx>
Cc: Andrea Arcangeli <aarcange@xxxxxxxxxx>
Cc: "Kirill A . Shutemov" <kirill.shutemov@xxxxxxxxxxxxxxx>
Cc: Michal Hocko <mhocko@xxxxxxxxxx>
---
 include/linux/vm_event_item.h | 1 +
 mm/vmscan.c                   | 3 +++
 mm/vmstat.c                   | 1 +
 3 files changed, 5 insertions(+)

diff --git a/include/linux/vm_event_item.h b/include/linux/vm_event_item.h
index c75024e80eed..e02820fc2861 100644
--- a/include/linux/vm_event_item.h
+++ b/include/linux/vm_event_item.h
@@ -86,6 +86,7 @@ enum vm_event_item { PGPGIN, PGPGOUT, PSWPIN, PSWPOUT,
 		THP_ZERO_PAGE_ALLOC,
 		THP_ZERO_PAGE_ALLOC_FAILED,
 		THP_SWPOUT,
+		THP_SWPOUT_FALLBACK,
 #endif
 #ifdef CONFIG_MEMORY_BALLOON
 		BALLOON_INFLATE,
diff --git a/mm/vmscan.c b/mm/vmscan.c
index f3abaef7c0b5..81703d6f9156 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -1153,6 +1153,9 @@ static unsigned long shrink_page_list(struct list_head *page_list,
 					if (split_huge_page_to_list(page,
 								    page_list))
 						goto activate_locked;
+#ifdef CONFIG_TRANSPARENT_HUGEPAGE
+					count_vm_event(THP_SWPOUT_FALLBACK);
+#endif
 					if (!add_to_swap(page))
 						goto activate_locked;
 				}
diff --git a/mm/vmstat.c b/mm/vmstat.c
index 243835d251a5..be5d427b4a1c 100644
--- a/mm/vmstat.c
+++ b/mm/vmstat.c
@@ -1072,6 +1072,7 @@ const char * const vmstat_text[] = {
 	"thp_zero_page_alloc",
 	"thp_zero_page_alloc_failed",
 	"thp_swpout",
+	"thp_swpout_fallback",
 #endif
 #ifdef CONFIG_MEMORY_BALLOON
 	"balloon_inflate",
-- 
2.11.0