From fe490cc0fe9e6ee48cc48bb5dc463bc5f0f1428f Mon Sep 17 00:00:00 2001
From: Huang Ying <ying.huang@intel.com>
Date: Wed, 6 Sep 2017 16:22:52 -0700
Subject: [PATCH] mm, THP, swap: add THP swapping out fallback counting

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.

Link: http://lkml.kernel.org/r/20170724051840.2309-13-ying.huang@intel.com
Signed-off-by: "Huang, Ying" <ying.huang@intel.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Hugh Dickins <hughd@google.com>
Cc: Shaohua Li <shli@kernel.org>
Cc: Rik van Riel <riel@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: "Kirill A . Shutemov" <kirill.shutemov@linux.intel.com>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Ross Zwisler <ross.zwisler@intel.com> [for brd.c, zram_drv.c, pmem.c]
Cc: Vishal L Verma <vishal.l.verma@intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
---
 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 6fbf707c0ce2..13d711dd8776 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -1154,6 +1154,9 @@ 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 bccf426453cd..e131b51654c7 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",
-- 
2.20.1