Add tracepoints to the slowpath code to gather some information.
The tracepoints can also be used to find out how much time was spent in
the slowpath.

Signed-off-by: Janani Ravichandran <redacted>
---
 include/trace/events/kmem.h | 40 ++++++++++++++++++++++++++++++++++++++++
 mm/page_alloc.c             |  5 +++++
 2 files changed, 45 insertions(+)

diff --git a/include/trace/events/kmem.h b/include/trace/events/kmem.h
index 6b2e154..c19ab9f 100644
--- a/include/trace/events/kmem.h
+++ b/include/trace/events/kmem.h

@@ -169,6 +169,46 @@ TRACE_EVENT(mm_page_free,
 			__entry->order)
 );
 
+TRACE_EVENT(mm_slowpath_begin,
+
+	TP_PROTO(gfp_t gfp_mask, int order),
+
+	TP_ARGS(gfp_mask, order),
+
+	TP_STRUCT__entry(
+		__field(gfp_t, gfp_mask)
+		__field(int, order)
+	),
+
+	TP_fast_assign(
+		__entry->gfp_mask = gfp_mask;
+		__entry->order = order;
+	),
+
+	TP_printk("gfp_mask:%s order=%d",
+		show_gfp_flags(__entry->gfp_mask),
+		__entry->order)
+);
+
+TRACE_EVENT(mm_slowpath_end,
+
+	TP_PROTO(struct page *page),
+
+	TP_ARGS(page),
+
+	TP_STRUCT__entry(
+		__field(unsigned long, pfn)
+	),
+
+	TP_fast_assign(
+		__entry->pfn = page ? page_to_pfn(page) : -1UL;
+	),
+
+	TP_printk("page=%p pfn=%lu",
+		__entry->pfn != -1UL ? pfn_to_page(__entry->pfn) : NULL,

+		__entry->pfn != -1UL ? __entry->pfn : 0)
+);
+
 TRACE_EVENT(mm_page_free_batched,
 
 	TP_PROTO(struct page *page, int cold),

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 8b3e134..be9c688 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c

@@ -3595,6 +3595,8 @@ __alloc_pages_slowpath(gfp_t gfp_mask, unsigned int order,
 				(__GFP_ATOMIC|__GFP_DIRECT_RECLAIM)))
 		gfp_mask &= ~__GFP_ATOMIC;
 
+	trace_mm_slowpath_begin(gfp_mask, order);
+
 retry:
 	if (gfp_mask & __GFP_KSWAPD_RECLAIM)
 		wake_all_kswapds(order, ac);

@@ -3769,6 +3771,9 @@ noretry:
 nopage:
 	warn_alloc_failed(gfp_mask, order, NULL);
 got_pg:
+
+	trace_mm_slowpath_end(page);
+