[PATCH 7/7] mm/vmstat: add NRSWP{IN,OUT} counters

[Christoph Hellwig <hch@lst.de>]

Count how many swap I/Os we cause.  Due to batching this can be different
than the current counter number of pages written/read, and tracking this
information is useful to see how efficient the batching is.

The counters are added at the end of enum vm_event_item and the
vmstat_text array under the assumption that the order of fields in
/proc/vmstat is an ABI.  If that is not the case, they could be grouped
with the other swap counters.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Nhat Pham <nphamcs@gmail.com>
---
 include/linux/vm_event_item.h | 4 ++++
 mm/page_io.c                  | 2 ++
 mm/vmstat.c                   | 6 +++++-
 3 files changed, 11 insertions(+), 1 deletion(-)

diff --git a/include/linux/vm_event_item.h b/include/linux/vm_event_item.h
index 03fe95f5a020..2628ccda076a 100644
--- a/include/linux/vm_event_item.h
+++ b/include/linux/vm_event_item.h
@@ -175,6 +175,10 @@ enum vm_event_item { PGPGIN, PGPGOUT, PSWPIN, PSWPOUT,
 		KSTACK_REST,
 #endif
 #endif /* CONFIG_DEBUG_STACK_USAGE */
+#ifdef CONFIG_SWAP
+		NRSWPIN,
+		NRSWPOUT,
+#endif /* CONFIG_SWAP */
 		NR_VM_EVENT_ITEMS
 };
 
diff --git a/mm/page_io.c b/mm/page_io.c
index 1e29b36cec07..c7681dbcfc76 100644
--- a/mm/page_io.c
+++ b/mm/page_io.c
@@ -703,6 +703,7 @@ void swap_write_submit(struct swap_io_ctx *ctx)
 {
 	if (!ctx->sio)
 		return;
+	count_vm_events(NRSWPOUT, 1);
 	ctx->sis->ops->submit_write(ctx);
 	ctx->sio = NULL;
 	ctx->sis = NULL;
@@ -712,6 +713,7 @@ void swap_read_submit(struct swap_io_ctx *ctx)
 {
 	if (!ctx->sio)
 		return;
+	count_vm_events(NRSWPIN, 1);
 	ctx->sis->ops->submit_read(ctx);
 	ctx->sio = NULL;
 	ctx->sis = NULL;
diff --git a/mm/vmstat.c b/mm/vmstat.c
index f534972f517d..9559f3c95735 100644
--- a/mm/vmstat.c
+++ b/mm/vmstat.c
@@ -1488,7 +1488,11 @@ const char * const vmstat_text[] = {
 #if THREAD_SIZE > 65536
 	[I(KSTACK_REST)]			= "kstack_rest",
 #endif
-#endif
+#endif /* CONFIG_DEBUG_STACK_USAGE */
+#ifdef CONFIG_SWAP
+	[I(NRSWPIN)]				= "nrswpin",
+	[I(NRSWPOUT)]				= "nrswpout",
+#endif /* CONFIG_SWAP */
 #undef I
 #endif /* CONFIG_VM_EVENT_COUNTERS */
 };
-- 
2.53.0