This looks like a nice cleanup to me. Thanks Vlastimil!
Reviewed-by: Axel Rasmussen <axelrasmussen@xxxxxxxxxx>
On Tue, Nov 5, 2024 at 3:35 AM Vlastimil Babka <vbabka@xxxxxxx> wrote:
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.
Cc: Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx>
Cc: Axel Rasmussen <axelrasmussen@xxxxxxxxxx>
Cc: Steven Rostedt <rostedt@xxxxxxxxxxx>
Cc: Masami Hiramatsu <mhiramat@xxxxxxxxxx>
Cc: Mathieu Desnoyers <mathieu.desnoyers@xxxxxxxxxxxx>
Signed-off-by: Vlastimil Babka <vbabka@xxxxxxx>
---
include/trace/events/mmap_lock.h | 14 ++++--------
mm/mmap_lock.c | 39 +++++++-------------------------
2 files changed, 12 insertions(+), 41 deletions(-)
diff --git a/include/trace/events/mmap_lock.h b/include/trace/events/mmap_lock.h
index f2827f98a44f..bc2e3ad787b3 100644
--- 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 368b840e7508..f186d57df2c6 100644
--- 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(®_refcount);
- return 0;
-}
-
-void trace_mmap_lock_unreg(void)
-{
- atomic_dec(®_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(®_refcount))
- return;
memcg = get_mem_cgroup_from_mm(mm);
if (memcg == NULL)
return;
--
2.47.0
