mm: mmap_lock: check trace_mmap_lock_$type_enabled() instead of regcount

Since 7d6be67cfdd4 ("mm: mmap_lock: replace get_memcg_path_buf() with
on-stack buffer") we use trace_mmap_lock_reg()/unreg() only to maintain an
atomic reg_refcount which is checked to avoid performing
get_mm_memcg_path() in case none of the tracepoints using it is enabled.

This can be achieved directly by putting all the work needed for the
tracepoint behind the trace_mmap_lock_##type##_enabled(), as suggested by
Documentation/trace/tracepoints.rst and with the following advantages:

- uses the tracepoint's static key instead of evaluating a branch

- the check tracepoint specific, not shared by all of them

- we can get rid of trace_mmap_lock_reg()/unreg() completely

Thus use the trace_..._enabled() check and remove unnecessary code.

Link: https://lkml.kernel.org/r/20241105113456.95066-2-vbabka@suse.cz
Signed-off-by: Vlastimil Babka <vbabka@suse.cz>
Reviewed-by: Axel Rasmussen <axelrasmussen@google.com>
Cc: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/include/trace/events/mmap_lock.h b/include/trace/events/mmap_lock.h
index f2827f98a44f39c08aeac63a963b548cfb1cb918..bc2e3ad787b3b0d090f835c3c6d1900c9555d05d 100644 (file)
--- a/include/trace/events/mmap_lock.h
+++ b/include/trace/events/mmap_lock.h
@@ -10,9 +10,6 @@
 
 struct mm_struct;
 
-extern int trace_mmap_lock_reg(void);
-extern void trace_mmap_lock_unreg(void);
-
 DECLARE_EVENT_CLASS(mmap_lock,
 
        TP_PROTO(struct mm_struct *mm, const char *memcg_path, bool write),
@@ -40,16 +37,15 @@ DECLARE_EVENT_CLASS(mmap_lock,
 );
 
 #define DEFINE_MMAP_LOCK_EVENT(name)                                    \
-       DEFINE_EVENT_FN(mmap_lock, name,                                \
+       DEFINE_EVENT(mmap_lock, name,                                   \
                TP_PROTO(struct mm_struct *mm, const char *memcg_path,  \
                        bool write),                                    \
-               TP_ARGS(mm, memcg_path, write),                         \
-               trace_mmap_lock_reg, trace_mmap_lock_unreg)
+               TP_ARGS(mm, memcg_path, write))
 
 DEFINE_MMAP_LOCK_EVENT(mmap_lock_start_locking);
 DEFINE_MMAP_LOCK_EVENT(mmap_lock_released);
 
-TRACE_EVENT_FN(mmap_lock_acquire_returned,
+TRACE_EVENT(mmap_lock_acquire_returned,
 
        TP_PROTO(struct mm_struct *mm, const char *memcg_path, bool write,
                bool success),
@@ -76,9 +72,7 @@ TRACE_EVENT_FN(mmap_lock_acquire_returned,
                __get_str(memcg_path),
                __entry->write ? "true" : "false",
                __entry->success ? "true" : "false"
-       ),
-
-       trace_mmap_lock_reg, trace_mmap_lock_unreg
+       )
 );
 
 #endif /* _TRACE_MMAP_LOCK_H */

diff --git a/mm/mmap_lock.c b/mm/mmap_lock.c
index 368b840e75082cfe2ea835853ccaac7368ccfd0d..f186d57df2c68e083995cb93872fa7b57769763c 100644 (file)
--- a/mm/mmap_lock.c
+++ b/mm/mmap_lock.c
@@ -19,43 +19,23 @@ EXPORT_TRACEPOINT_SYMBOL(mmap_lock_released);
 
 #ifdef CONFIG_MEMCG
 
-static atomic_t reg_refcount;
-
 /*
  * Size of the buffer for memcg path names. Ignoring stack trace support,
  * trace_events_hist.c uses MAX_FILTER_STR_VAL for this, so we also use it.
  */
 #define MEMCG_PATH_BUF_SIZE MAX_FILTER_STR_VAL
 
-int trace_mmap_lock_reg(void)
-{
-       atomic_inc(&reg_refcount);
-       return 0;
-}
-
-void trace_mmap_lock_unreg(void)
-{
-       atomic_dec(&reg_refcount);
-}
-
-#define TRACE_MMAP_LOCK_EVENT(type, mm, ...)                    \
-       do {                                                    \
-               char buf[MEMCG_PATH_BUF_SIZE];                  \
-               get_mm_memcg_path(mm, buf, sizeof(buf));        \
-               trace_mmap_lock_##type(mm, buf, ##__VA_ARGS__); \
+#define TRACE_MMAP_LOCK_EVENT(type, mm, ...)                           \
+       do {                                                            \
+               if (trace_mmap_lock_##type##_enabled()) {               \
+                       char buf[MEMCG_PATH_BUF_SIZE];                  \
+                       get_mm_memcg_path(mm, buf, sizeof(buf));        \
+                       trace_mmap_lock_##type(mm, buf, ##__VA_ARGS__); \
+               }                                                       \
        } while (0)
 
 #else /* !CONFIG_MEMCG */
 
-int trace_mmap_lock_reg(void)
-{
-       return 0;
-}
-
-void trace_mmap_lock_unreg(void)
-{
-}
-
 #define TRACE_MMAP_LOCK_EVENT(type, mm, ...)                                   \
        trace_mmap_lock_##type(mm, "", ##__VA_ARGS__)
 
@@ -65,16 +45,13 @@ void trace_mmap_lock_unreg(void)
 #ifdef CONFIG_MEMCG
 /*
  * Write the given mm_struct's memcg path to a buffer. If the path cannot be
- * determined or the trace event is being unregistered, empty string is written.
+ * determined, empty string is written.
  */
 static void get_mm_memcg_path(struct mm_struct *mm, char *buf, size_t buflen)
 {
        struct mem_cgroup *memcg;
 
        buf[0] = '\0';
-       /* No need to get path if no trace event is registered. */
-       if (!atomic_read(&reg_refcount))
-               return;
        memcg = get_mem_cgroup_from_mm(mm);
        if (memcg == NULL)
                return;