linux-kernel - [PATCH 3/3] mm: mmap_lock: add ip to mmap

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Message-Id: <20210729092853.38242-1-ligang.bdlg@bytedance.com>
Date:   Thu, 29 Jul 2021 17:28:53 +0800
From:   Gang Li <ligang.bdlg@...edance.com>
To:     rostedt@...dmis.org
Cc:     mingo@...hat.com, akpm@...ux-foundation.org, vbabka@...e.cz,
        axelrasmussen@...gle.com, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, Gang Li <ligang.bdlg@...edance.com>
Subject: [PATCH 3/3] mm: mmap_lock: add ip to mmap_lock tracepoints

The mmap_lock is acquired on most (all?) mmap / munmap / page fault
operations, so a multi-threaded process which does a lot of these
can experience significant contention. Sometimes we want to know
where the lock is hold. And it's hard to locate without collecting ip.

Here's an example: TP_printk("ip=%pS",ip)
Log looks like this: "ip=do_user_addr_fault+0x274/0x640"

We can find out who cause the contention amd make some improvements
for it.

Signed-off-by: Gang Li <ligang.bdlg@...edance.com>
---
 include/trace/events/mmap_lock.h | 27 +++++++++++++++++----------
 mm/mmap_lock.c                   |  6 +++---
 2 files changed, 20 insertions(+), 13 deletions(-)

diff --git a/include/trace/events/mmap_lock.h b/include/trace/events/mmap_lock.h
index b9dd66f9c226..8913a9f85894 100644
--- a/include/trace/events/mmap_lock.h
+++ b/include/trace/events/mmap_lock.h
@@ -15,35 +15,39 @@ extern void trace_mmap_lock_unreg(void);
 
 DECLARE_EVENT_CLASS(mmap_lock,
 
-	TP_PROTO(struct mm_struct *mm, const char *memcg_path, bool write),
+	TP_PROTO(struct mm_struct *mm, const char *memcg_path, bool write,
+		unsigned long ip),
 
-	TP_ARGS(mm, memcg_path, write),
+	TP_ARGS(mm, memcg_path, write, ip),
 
 	TP_STRUCT__entry(
 		__field(struct mm_struct *, mm)
 		__string(memcg_path, memcg_path)
 		__field(bool, write)
+		__field(void *, ip)
 	),
 
 	TP_fast_assign(
 		__entry->mm = mm;
 		__assign_str(memcg_path, memcg_path);
 		__entry->write = write;
+		__entry->ip = (void *)ip;
 	),
 
 	TP_printk(
-		"mm=%p memcg_path=%s write=%s",
+		"mm=%p memcg_path=%s write=%s ip=%pS",
 		__entry->mm,
 		__get_str(memcg_path),
-		__entry->write ? "true" : "false"
-   )
+		__entry->write ? "true" : "false",
+		__entry->ip
+	)
 );
 
 #define DEFINE_MMAP_LOCK_EVENT(name)                                    \
 	DEFINE_EVENT_FN(mmap_lock, name,                                \
 		TP_PROTO(struct mm_struct *mm, const char *memcg_path,  \
-			bool write),                                    \
-		TP_ARGS(mm, memcg_path, write),                         \
+			bool write, unsigned long ip),                  \
+		TP_ARGS(mm, memcg_path, write, ip),                     \
 		trace_mmap_lock_reg, trace_mmap_lock_unreg)
 
 DEFINE_MMAP_LOCK_EVENT(mmap_lock_start_locking);
@@ -52,14 +56,15 @@ DEFINE_MMAP_LOCK_EVENT(mmap_lock_released);
 TRACE_EVENT_FN(mmap_lock_acquire_returned,
 
 	TP_PROTO(struct mm_struct *mm, const char *memcg_path, bool write,
-		bool success),
+		unsigned long ip, bool success),
 
-	TP_ARGS(mm, memcg_path, write, success),
+	TP_ARGS(mm, memcg_path, write, ip, success),
 
 	TP_STRUCT__entry(
 		__field(struct mm_struct *, mm)
 		__string(memcg_path, memcg_path)
 		__field(bool, write)
+		__field(void *, ip)
 		__field(bool, success)
 	),
 
@@ -67,14 +72,16 @@ TRACE_EVENT_FN(mmap_lock_acquire_returned,
 		__entry->mm = mm;
 		__assign_str(memcg_path, memcg_path);
 		__entry->write = write;
+		__entry->ip = (void *)ip;
 		__entry->success = success;
 	),
 
 	TP_printk(
-		"mm=%p memcg_path=%s write=%s success=%s",
+		"mm=%p memcg_path=%s write=%s ip=%pS success=%s",
 		__entry->mm,
 		__get_str(memcg_path),
 		__entry->write ? "true" : "false",
+		__entry->ip,
 		__entry->success ? "true" : "false"
 	),
 
diff --git a/mm/mmap_lock.c b/mm/mmap_lock.c
index 1854850b4b89..f1100eae6f2f 100644
--- a/mm/mmap_lock.c
+++ b/mm/mmap_lock.c
@@ -227,20 +227,20 @@ static const char *get_mm_memcg_path(struct mm_struct *mm)
 
 void __mmap_lock_do_trace_start_locking(struct mm_struct *mm, bool write)
 {
-	TRACE_MMAP_LOCK_EVENT(start_locking, mm, write);
+	TRACE_MMAP_LOCK_EVENT(start_locking, mm, write, _RET_IP_);
 }
 EXPORT_SYMBOL(__mmap_lock_do_trace_start_locking);
 
 void __mmap_lock_do_trace_acquire_returned(struct mm_struct *mm, bool write,
 					   bool success)
 {
-	TRACE_MMAP_LOCK_EVENT(acquire_returned, mm, write, success);
+	TRACE_MMAP_LOCK_EVENT(acquire_returned, mm, write, _RET_IP_, success);
 }
 EXPORT_SYMBOL(__mmap_lock_do_trace_acquire_returned);
 
 void __mmap_lock_do_trace_released(struct mm_struct *mm, bool write)
 {
-	TRACE_MMAP_LOCK_EVENT(released, mm, write);
+	TRACE_MMAP_LOCK_EVENT(released, mm, write, _RET_IP_);
 }
 EXPORT_SYMBOL(__mmap_lock_do_trace_released);
 #endif /* CONFIG_TRACING */
-- 
2.20.1