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

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Since 7d6be67cfd ("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>
This commit is contained in:
Vlastimil Babka 2024-11-05 12:34:57 +01:00 committed by Andrew Morton
parent 9f3310ccc7
commit 9b5c87d479
2 changed files with 12 additions and 41 deletions
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14
include/trace/events/mmap_lock.h
View File

@ -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 */

39
mm/mmap_lock.c
View File

@ -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;