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[PATCH -V6 10/21] swap: Support to count THP swapin and its fallback




2 new /proc/vmstat fields are added, "thp_swapin" and
"thp_swapin_fallback" to count swapin a THP from swap device in one
piece and fallback to normal page swapin.

Signed-off-by: "Huang, Ying" <ying.huang@xxxxxxxxx>
Cc: "Kirill A. Shutemov" <kirill.shutemov@xxxxxxxxxxxxxxx>
Cc: Andrea Arcangeli <aarcange@xxxxxxxxxx>
Cc: Michal Hocko <mhocko@xxxxxxxxxx>
Cc: Johannes Weiner <hannes@xxxxxxxxxxx>
Cc: Shaohua Li <shli@xxxxxxxxxx>
Cc: Hugh Dickins <hughd@xxxxxxxxxx>
Cc: Minchan Kim <minchan@xxxxxxxxxx>
Cc: Rik van Riel <riel@xxxxxxxxxx>
Cc: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
Cc: Naoya Horiguchi <n-horiguchi@xxxxxxxxxxxxx>
Cc: Zi Yan <zi.yan@xxxxxxxxxxxxxx>
Cc: Daniel Jordan <daniel.m.jordan@xxxxxxxxxx>
---
 Documentation/admin-guide/mm/transhuge.rst |  8 ++++++++
 include/linux/vm_event_item.h              |  2 ++
 mm/huge_memory.c                           |  4 +++-
 mm/page_io.c                               | 15 ++++++++++++---
 mm/vmstat.c                                |  2 ++
 5 files changed, 27 insertions(+), 4 deletions(-)

diff --git a/Documentation/admin-guide/mm/transhuge.rst b/Documentation/admin-guide/mm/transhuge.rst
index 7ab93a8404b9..85e33f785fd7 100644
--- a/Documentation/admin-guide/mm/transhuge.rst
+++ b/Documentation/admin-guide/mm/transhuge.rst
@@ -364,6 +364,14 @@ thp_swpout_fallback
 	Usually because failed to allocate some continuous swap space
 	for the huge page.
 
+thp_swpin
+	is incremented every time a huge page is swapin in one piece
+	without splitting.
+
+thp_swpin_fallback
+	is incremented if a huge page has to be split during swapin.
+	Usually because failed to allocate a huge page.
+
 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
diff --git a/include/linux/vm_event_item.h b/include/linux/vm_event_item.h
index 47a3441cf4c4..c20b655cfdcc 100644
--- a/include/linux/vm_event_item.h
+++ b/include/linux/vm_event_item.h
@@ -88,6 +88,8 @@ enum vm_event_item { PGPGIN, PGPGOUT, PSWPIN, PSWPOUT,
 		THP_ZERO_PAGE_ALLOC_FAILED,
 		THP_SWPOUT,
 		THP_SWPOUT_FALLBACK,
+		THP_SWPIN,
+		THP_SWPIN_FALLBACK,
 #endif
 #ifdef CONFIG_MEMORY_BALLOON
 		BALLOON_INFLATE,
diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index fbc9c9e30992..8efcc84fb4b0 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -1715,8 +1715,10 @@ int do_huge_pmd_swap_page(struct vm_fault *vmf, pmd_t orig_pmd)
 				/* swapoff occurs under us */
 				} else if (ret == -EINVAL)
 					ret = 0;
-				else
+				else {
+					count_vm_event(THP_SWPIN_FALLBACK);
 					goto fallback;
+				}
 			}
 			delayacct_clear_flag(DELAYACCT_PF_SWAPIN);
 			goto out;
diff --git a/mm/page_io.c b/mm/page_io.c
index 573d3663d846..bcc2da750590 100644
--- a/mm/page_io.c
+++ b/mm/page_io.c
@@ -348,6 +348,15 @@ int __swap_writepage(struct page *page, struct writeback_control *wbc,
 	return ret;
 }
 
+static inline void count_swpin_vm_event(struct page *page)
+{
+#ifdef CONFIG_TRANSPARENT_HUGEPAGE
+	if (unlikely(PageTransHuge(page)))
+		count_vm_event(THP_SWPIN);
+#endif
+	count_vm_events(PSWPIN, hpage_nr_pages(page));
+}
+
 int swap_readpage(struct page *page, bool synchronous)
 {
 	struct bio *bio;
@@ -371,7 +380,7 @@ int swap_readpage(struct page *page, bool synchronous)
 
 		ret = mapping->a_ops->readpage(swap_file, page);
 		if (!ret)
-			count_vm_event(PSWPIN);
+			count_swpin_vm_event(page);
 		return ret;
 	}
 
@@ -382,7 +391,7 @@ int swap_readpage(struct page *page, bool synchronous)
 			unlock_page(page);
 		}
 
-		count_vm_event(PSWPIN);
+		count_swpin_vm_event(page);
 		return 0;
 	}
 
@@ -401,7 +410,7 @@ int swap_readpage(struct page *page, bool synchronous)
 	get_task_struct(current);
 	bio->bi_private = current;
 	bio_set_op_attrs(bio, REQ_OP_READ, 0);
-	count_vm_event(PSWPIN);
+	count_swpin_vm_event(page);
 	bio_get(bio);
 	qc = submit_bio(bio);
 	while (synchronous) {
diff --git a/mm/vmstat.c b/mm/vmstat.c
index d08ed044759d..823856fae136 100644
--- a/mm/vmstat.c
+++ b/mm/vmstat.c
@@ -1264,6 +1264,8 @@ const char * const vmstat_text[] = {
 	"thp_zero_page_alloc_failed",
 	"thp_swpout",
 	"thp_swpout_fallback",
+	"thp_swpin",
+	"thp_swpin_fallback",
 #endif
 #ifdef CONFIG_MEMORY_BALLOON
 	"balloon_inflate",
-- 
2.16.4