[PATCH v4 1/5] mm/rmap: add tracepoint for rmap_walk

[xu.xin16]

From: xu xin <xu.xin16@xxxxxxxxxx>

Add a new tracepoint rmap_walk in mm/rmap.c to monitor reverse mapping
traversal. The tracepoint records the duration (in nanoseconds), the
type of the folio (KSM, anonymous, or file-backed), and the addresses
of the folio and rmap_walk_control structures. The type determination
is performed inside the tracepoint to keep the function itself
lightweight.

'# cat /sys/kernel/tracing/trace
'# tracer: nop
'#
'# entries-in-buffer/entries-written: 408/408   #P:4
'#
'#                     _-----=> irqs-off/BH-disabled
'#                    / _----=> need-resched
'#                   | / _---=> hardirq/softirq
'#                   || / _--=> preempt-depth
'#                   ||| / _-=> migrate-disable
'#                   |||| /     delay
'#TASK-PID     CPU#  |||||  TIMESTAMP  FUNCTION
'#   | |         |   |||||     |         |
rmap-215     [001] .....   692.237079: rmap_walk: folio=000000000029ddcb rwc=00000000dac4cda0 duration_ns=828682 page_type=ksm locked=false
rmap-215     [001] .....   692.239480: rmap_walk: folio=0000000092a21fd3 rwc=00000000986376ff duration_ns=905966 page_type=ksm locked=false
rmap-230     [003] .....   692.583619: rmap_walk: folio=0000000037a237b6 rwc=0000000080fbbb0a duration_ns=107892 page_type=ksm locked=false
rmap-230     [003] .....   692.584104: rmap_walk: folio=0000000031bdbf8b rwc=00000000b39c973a duration_ns=330886 page_type=ksm locked=false
rmap-244     [003] .....   692.708706: rmap_walk: folio=000000009105fa6b rwc=0000000037d46cd7 duration_ns=987826 page_type=file locked=false
rmap-244     [003] .....   692.709198: rmap_walk: folio=000000009105fa6b rwc=0000000093942e2c duration_ns=161733 page_type=file locked=false
rmap-244     [003] .....   692.709606: rmap_walk: folio=000000009105fa6b rwc=0000000037d46cd7 duration_ns=54428 page_type=file locked=false
rmap-244     [003] .....   692.709658: rmap_walk: folio=000000009105fa6b rwc=0000000093942e2c duration_ns=27192 page_type=file locked=false

Signed-off-by: xu xin <xu.xin16@xxxxxxxxxx>
---
 include/trace/events/rmap.h | 49 +++++++++++++++++++++++++++++++++++++
 mm/rmap.c                   | 14 +++++++++++
 2 files changed, 63 insertions(+)
 create mode 100644 include/trace/events/rmap.h

diff --git a/include/trace/events/rmap.h b/include/trace/events/rmap.h
new file mode 100644
index 000000000000..987fa204d65d
--- /dev/null
+++ b/include/trace/events/rmap.h
@@ -0,0 +1,49 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#undef TRACE_SYSTEM
+#define TRACE_SYSTEM rmap
+
+#if !defined(_TRACE_RMAP_H) || defined(TRACE_HEADER_MULTI_READ)
+#define _TRACE_RMAP_H
+
+#include <linux/tracepoint.h>
+#include <linux/rmap.h>
+
+#define GET_RMAP_PAGE_TYPE(folio) (folio_test_ksm(folio) ? "ksm" : \
+		(folio_test_anon(folio) ? "anon" : "file"))
+
+TRACE_EVENT(rmap_walk,
+
+	TP_PROTO(struct folio *folio, struct rmap_walk_control *rwc, u64 duration_ns, bool locked),
+
+	TP_ARGS(folio, rwc, duration_ns, locked),
+
+	TP_STRUCT__entry(
+		__field(unsigned long, folio_addr)
+		__field(unsigned long, rwc_addr)
+		__field(u64, duration_ns)
+		__string(page_type, GET_RMAP_PAGE_TYPE(folio))
+		__field(bool, locked)
+	),
+
+	TP_fast_assign(
+		__entry->folio_addr = (unsigned long)folio;
+		__entry->rwc_addr = (unsigned long)rwc;
+		__entry->duration_ns = duration_ns;
+		__assign_str(page_type);
+		__entry->locked = locked;
+	),
+
+	TP_printk("folio=%p rwc=%p duration_ns=%llu page_type=%s locked=%s",
+		(void *)(unsigned long)__entry->folio_addr,
+		(void *)(unsigned long)__entry->rwc_addr,
+		__entry->duration_ns,
+		__get_str(page_type),
+		__entry->locked ? "true" : "false")
+);
+
+
+
+#endif /* _TRACE_RMAP_H */
+
+/* This part must be outside protection */
+#include <trace/define_trace.h>
diff --git a/mm/rmap.c b/mm/rmap.c
index 78b7fb5f367c..14bf8483f38b 100644
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -75,11 +75,13 @@
 #include <linux/userfaultfd_k.h>
 #include <linux/mm_inline.h>
 #include <linux/oom.h>
+#include <linux/sched/clock.h>

 #include <asm/tlb.h>

 #define CREATE_TRACE_POINTS
 #include <trace/events/migrate.h>
+#include <trace/events/rmap.h>

 #include "internal.h"
 #include "swap.h"
@@ -3098,23 +3100,35 @@ static void rmap_walk_file(struct folio *folio,

 void rmap_walk(struct folio *folio, struct rmap_walk_control *rwc)
 {
+	u64 ts_start, delta_ns;
+	ts_start = local_clock();
+
 	if (unlikely(folio_test_ksm(folio)))
 		rmap_walk_ksm(folio, rwc);
 	else if (folio_test_anon(folio))
 		rmap_walk_anon(folio, rwc, false);
 	else
 		rmap_walk_file(folio, rwc, false);
+
+	delta_ns = local_clock() - ts_start;
+	trace_rmap_walk(folio, rwc, delta_ns, false);
 }

 /* Like rmap_walk, but caller holds relevant rmap lock */
 void rmap_walk_locked(struct folio *folio, struct rmap_walk_control *rwc)
 {
+	u64 ts_start, delta_ns;
+	ts_start = local_clock();
+
 	/* no ksm support for now */
 	VM_BUG_ON_FOLIO(folio_test_ksm(folio), folio);
 	if (folio_test_anon(folio))
 		rmap_walk_anon(folio, rwc, true);
 	else
 		rmap_walk_file(folio, rwc, true);
+
+	delta_ns = local_clock() - ts_start;
+	trace_rmap_walk(folio, rwc, delta_ns, true);
 }

 #ifdef CONFIG_HUGETLB_PAGE
-- 
2.25.1