| Message ID | 20241123060939.169978-1-shakeel.butt@linux.dev (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | mm: mmap_lock: optimize mmap_lock tracepoints | expand |
On Fri, Nov 22, 2024 at 10:10 PM Shakeel Butt <shakeel.butt@linux.dev> wrote: > > We are starting to deploy mmap_lock tracepoint monitoring across our > fleet and the early results showed that these tracepoints are consuming > significant amount of CPUs in kernfs_path_from_node when enabled. > > It seems like the kernel is trying to resolved the cgroup path in the s/resolved/resolve > fast path of the locking code path when the tracepoints are enabled. In > addition for some application their metrics are regressing when > monitoring is enabled. > > The cgroup path resolution can be slow and should not be done in the > fast path. Most userspace tools, like bpftrace, provides functionality > to get the cgroup path from cgroup id, so let's just trace the cgroup > id and the users can use better tools to get the path in the slow path. > > Signed-off-by: Shakeel Butt <shakeel.butt@linux.dev> > --- > include/linux/memcontrol.h | 18 ++++++++++++ > include/trace/events/mmap_lock.h | 32 ++++++++++---------- > mm/mmap_lock.c | 50 ++------------------------------ > 3 files changed, 36 insertions(+), 64 deletions(-) > > diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h > index 5502aa8e138e..d82f08cd70cd 100644 > --- a/include/linux/memcontrol.h > +++ b/include/linux/memcontrol.h > @@ -1046,6 +1046,19 @@ static inline void memcg_memory_event_mm(struct mm_struct *mm, > > void split_page_memcg(struct page *head, int old_order, int new_order); > > +static inline u64 memcg_id_from_mm(struct mm_struct *mm) The usage of memcg_id here and throughout the patch is a bit confusing because we have a member called 'id' in struct mem_cgroup, but this isn't it. This is the cgroup_id of the memcg. I admit it's hard to distinguish them during naming, but when I first saw the function I thought it was returning memcg->id. Maybe just cgroup_id_from_mm()? In cgroup v2, the cgroup id is the same regardless of the controller anyway, in cgroup v1, it's kinda natural that we return the cgroup id of the memcg. I don't feel strongly, but I prefer that we use clearer naming, and either way a comment may help clarify things. > +{ > + struct mem_cgroup *memcg; > + u64 id = 0; > + > + rcu_read_lock(); > + memcg = mem_cgroup_from_task(rcu_dereference(mm->owner)); > + if (likely(memcg)) > + id = cgroup_id(memcg->css.cgroup); We return 0 if the memcg is NULL here, shouldn't we return the cgroup id of the root memcg instead? This is more consistent with get_mem_cgroup_from_mm(), and makes sure we always return the id of a valid cgroup. > + rcu_read_unlock(); > + return id; > +} > + > #else /* CONFIG_MEMCG */ > > #define MEM_CGROUP_ID_SHIFT 0 > @@ -1466,6 +1479,11 @@ void count_memcg_event_mm(struct mm_struct *mm, enum vm_event_item idx) > static inline void split_page_memcg(struct page *head, int old_order, int new_order) > { > } > + > +static inline u64 memcg_id_from_mm(struct mm_struct *mm) > +{ > + return 0; > +} > #endif /* CONFIG_MEMCG */ > > /* > diff --git a/include/trace/events/mmap_lock.h b/include/trace/events/mmap_lock.h > index bc2e3ad787b3..5529933d19c5 100644 > --- a/include/trace/events/mmap_lock.h > +++ b/include/trace/events/mmap_lock.h > @@ -5,6 +5,7 @@ > #if !defined(_TRACE_MMAP_LOCK_H) || defined(TRACE_HEADER_MULTI_READ) > #define _TRACE_MMAP_LOCK_H > > +#include <linux/memcontrol.h> > #include <linux/tracepoint.h> > #include <linux/types.h> > > @@ -12,64 +13,61 @@ struct mm_struct; > > DECLARE_EVENT_CLASS(mmap_lock, > > - TP_PROTO(struct mm_struct *mm, const char *memcg_path, bool write), > + TP_PROTO(struct mm_struct *mm, bool write), > > - TP_ARGS(mm, memcg_path, write), > + TP_ARGS(mm, write), > > TP_STRUCT__entry( > __field(struct mm_struct *, mm) > - __string(memcg_path, memcg_path) > + __field(u64, memcg_id) > __field(bool, write) > ), > > TP_fast_assign( > __entry->mm = mm; > - __assign_str(memcg_path); > + __entry->memcg_id = memcg_id_from_mm(mm); > __entry->write = write; > ), > > TP_printk( > - "mm=%p memcg_path=%s write=%s", > - __entry->mm, > - __get_str(memcg_path), > + "mm=%p memcg_id=%llu write=%s", > + __entry->mm, __entry->memcg_id, > __entry->write ? "true" : "false" > ) > ); > > #define DEFINE_MMAP_LOCK_EVENT(name) \ > DEFINE_EVENT(mmap_lock, name, \ > - TP_PROTO(struct mm_struct *mm, const char *memcg_path, \ > - bool write), \ > - TP_ARGS(mm, memcg_path, write)) > + TP_PROTO(struct mm_struct *mm, bool write), \ > + TP_ARGS(mm, write)) > > DEFINE_MMAP_LOCK_EVENT(mmap_lock_start_locking); > DEFINE_MMAP_LOCK_EVENT(mmap_lock_released); > > TRACE_EVENT(mmap_lock_acquire_returned, > > - TP_PROTO(struct mm_struct *mm, const char *memcg_path, bool write, > - bool success), > + TP_PROTO(struct mm_struct *mm, bool write, bool success), > > - TP_ARGS(mm, memcg_path, write, success), > + TP_ARGS(mm, write, success), > > TP_STRUCT__entry( > __field(struct mm_struct *, mm) > - __string(memcg_path, memcg_path) > + __field(u64, memcg_id) > __field(bool, write) > __field(bool, success) > ), > > TP_fast_assign( > __entry->mm = mm; > - __assign_str(memcg_path); > + __entry->memcg_id = memcg_id_from_mm(mm); > __entry->write = write; > __entry->success = success; > ), > > TP_printk( > - "mm=%p memcg_path=%s write=%s success=%s", > + "mm=%p memcg_id=%llu write=%s success=%s", > __entry->mm, > - __get_str(memcg_path), > + __entry->memcg_id, > __entry->write ? "true" : "false", > __entry->success ? "true" : "false" > ) > diff --git a/mm/mmap_lock.c b/mm/mmap_lock.c > index f186d57df2c6..e7dbaf96aa17 100644 > --- a/mm/mmap_lock.c > +++ b/mm/mmap_lock.c > @@ -17,51 +17,7 @@ EXPORT_TRACEPOINT_SYMBOL(mmap_lock_start_locking); > EXPORT_TRACEPOINT_SYMBOL(mmap_lock_acquire_returned); > EXPORT_TRACEPOINT_SYMBOL(mmap_lock_released); > > -#ifdef CONFIG_MEMCG > - > -/* > - * 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 > - > -#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 */ > - > -#define TRACE_MMAP_LOCK_EVENT(type, mm, ...) \ > - trace_mmap_lock_##type(mm, "", ##__VA_ARGS__) > - > -#endif /* CONFIG_MEMCG */ > - > #ifdef CONFIG_TRACING > -#ifdef CONFIG_MEMCG > -/* > - * Write the given mm_struct's memcg path to a buffer. If the path cannot be > - * 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'; > - memcg = get_mem_cgroup_from_mm(mm); > - if (memcg == NULL) > - return; > - if (memcg->css.cgroup) > - cgroup_path(memcg->css.cgroup, buf, buflen); > - css_put(&memcg->css); > -} > - > -#endif /* CONFIG_MEMCG */ > - > /* > * Trace calls must be in a separate file, as otherwise there's a circular > * dependency between linux/mmap_lock.h and trace/events/mmap_lock.h. > @@ -69,20 +25,20 @@ static void get_mm_memcg_path(struct mm_struct *mm, char *buf, size_t buflen) > > void __mmap_lock_do_trace_start_locking(struct mm_struct *mm, bool write) > { > - TRACE_MMAP_LOCK_EVENT(start_locking, mm, write); > + trace_mmap_lock_start_locking(mm, write); > } > 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_acquire_returned(mm, write, 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_released(mm, write); > } > EXPORT_SYMBOL(__mmap_lock_do_trace_released); > #endif /* CONFIG_TRACING */ > -- > 2.43.5 > >
On 11/23/24 7:09 AM, Shakeel Butt wrote: > We are starting to deploy mmap_lock tracepoint monitoring across our > fleet and the early results showed that these tracepoints are consuming > significant amount of CPUs in kernfs_path_from_node when enabled. > > It seems like the kernel is trying to resolved the cgroup path in the > fast path of the locking code path when the tracepoints are enabled. In > addition for some application their metrics are regressing when > monitoring is enabled. > > The cgroup path resolution can be slow and should not be done in the > fast path. Most userspace tools, like bpftrace, provides functionality > to get the cgroup path from cgroup id, so let's just trace the cgroup > id and the users can use better tools to get the path in the slow path. > > Signed-off-by: Shakeel Butt <shakeel.butt@linux.dev> AFAIU this would also remove the lockdep issue that patch [1] is solving with RCU conversion. It probably has other benefits on its own too, so just FYI. It's definitely better to avoid complex operations to gather tracepoint data, if avoidable. [1] https://lore.kernel.org/all/20241121175250.EJbI7VMb@linutronix.de/ > --- > include/linux/memcontrol.h | 18 ++++++++++++ > include/trace/events/mmap_lock.h | 32 ++++++++++---------- > mm/mmap_lock.c | 50 ++------------------------------ > 3 files changed, 36 insertions(+), 64 deletions(-) > > diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h > index 5502aa8e138e..d82f08cd70cd 100644 > --- a/include/linux/memcontrol.h > +++ b/include/linux/memcontrol.h > @@ -1046,6 +1046,19 @@ static inline void memcg_memory_event_mm(struct mm_struct *mm, > > void split_page_memcg(struct page *head, int old_order, int new_order); > > +static inline u64 memcg_id_from_mm(struct mm_struct *mm) > +{ > + struct mem_cgroup *memcg; > + u64 id = 0; > + > + rcu_read_lock(); > + memcg = mem_cgroup_from_task(rcu_dereference(mm->owner)); > + if (likely(memcg)) > + id = cgroup_id(memcg->css.cgroup); > + rcu_read_unlock(); > + return id; > +} > + > #else /* CONFIG_MEMCG */ > > #define MEM_CGROUP_ID_SHIFT 0 > @@ -1466,6 +1479,11 @@ void count_memcg_event_mm(struct mm_struct *mm, enum vm_event_item idx) > static inline void split_page_memcg(struct page *head, int old_order, int new_order) > { > } > + > +static inline u64 memcg_id_from_mm(struct mm_struct *mm) > +{ > + return 0; > +} > #endif /* CONFIG_MEMCG */ > > /* > diff --git a/include/trace/events/mmap_lock.h b/include/trace/events/mmap_lock.h > index bc2e3ad787b3..5529933d19c5 100644 > --- a/include/trace/events/mmap_lock.h > +++ b/include/trace/events/mmap_lock.h > @@ -5,6 +5,7 @@ > #if !defined(_TRACE_MMAP_LOCK_H) || defined(TRACE_HEADER_MULTI_READ) > #define _TRACE_MMAP_LOCK_H > > +#include <linux/memcontrol.h> > #include <linux/tracepoint.h> > #include <linux/types.h> > > @@ -12,64 +13,61 @@ struct mm_struct; > > DECLARE_EVENT_CLASS(mmap_lock, > > - TP_PROTO(struct mm_struct *mm, const char *memcg_path, bool write), > + TP_PROTO(struct mm_struct *mm, bool write), > > - TP_ARGS(mm, memcg_path, write), > + TP_ARGS(mm, write), > > TP_STRUCT__entry( > __field(struct mm_struct *, mm) > - __string(memcg_path, memcg_path) > + __field(u64, memcg_id) > __field(bool, write) > ), > > TP_fast_assign( > __entry->mm = mm; > - __assign_str(memcg_path); > + __entry->memcg_id = memcg_id_from_mm(mm); > __entry->write = write; > ), > > TP_printk( > - "mm=%p memcg_path=%s write=%s", > - __entry->mm, > - __get_str(memcg_path), > + "mm=%p memcg_id=%llu write=%s", > + __entry->mm, __entry->memcg_id, > __entry->write ? "true" : "false" > ) > ); > > #define DEFINE_MMAP_LOCK_EVENT(name) \ > DEFINE_EVENT(mmap_lock, name, \ > - TP_PROTO(struct mm_struct *mm, const char *memcg_path, \ > - bool write), \ > - TP_ARGS(mm, memcg_path, write)) > + TP_PROTO(struct mm_struct *mm, bool write), \ > + TP_ARGS(mm, write)) > > DEFINE_MMAP_LOCK_EVENT(mmap_lock_start_locking); > DEFINE_MMAP_LOCK_EVENT(mmap_lock_released); > > TRACE_EVENT(mmap_lock_acquire_returned, > > - TP_PROTO(struct mm_struct *mm, const char *memcg_path, bool write, > - bool success), > + TP_PROTO(struct mm_struct *mm, bool write, bool success), > > - TP_ARGS(mm, memcg_path, write, success), > + TP_ARGS(mm, write, success), > > TP_STRUCT__entry( > __field(struct mm_struct *, mm) > - __string(memcg_path, memcg_path) > + __field(u64, memcg_id) > __field(bool, write) > __field(bool, success) > ), > > TP_fast_assign( > __entry->mm = mm; > - __assign_str(memcg_path); > + __entry->memcg_id = memcg_id_from_mm(mm); > __entry->write = write; > __entry->success = success; > ), > > TP_printk( > - "mm=%p memcg_path=%s write=%s success=%s", > + "mm=%p memcg_id=%llu write=%s success=%s", > __entry->mm, > - __get_str(memcg_path), > + __entry->memcg_id, > __entry->write ? "true" : "false", > __entry->success ? "true" : "false" > ) > diff --git a/mm/mmap_lock.c b/mm/mmap_lock.c > index f186d57df2c6..e7dbaf96aa17 100644 > --- a/mm/mmap_lock.c > +++ b/mm/mmap_lock.c > @@ -17,51 +17,7 @@ EXPORT_TRACEPOINT_SYMBOL(mmap_lock_start_locking); > EXPORT_TRACEPOINT_SYMBOL(mmap_lock_acquire_returned); > EXPORT_TRACEPOINT_SYMBOL(mmap_lock_released); > > -#ifdef CONFIG_MEMCG > - > -/* > - * 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 > - > -#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 */ > - > -#define TRACE_MMAP_LOCK_EVENT(type, mm, ...) \ > - trace_mmap_lock_##type(mm, "", ##__VA_ARGS__) > - > -#endif /* CONFIG_MEMCG */ > - > #ifdef CONFIG_TRACING > -#ifdef CONFIG_MEMCG > -/* > - * Write the given mm_struct's memcg path to a buffer. If the path cannot be > - * 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'; > - memcg = get_mem_cgroup_from_mm(mm); > - if (memcg == NULL) > - return; > - if (memcg->css.cgroup) > - cgroup_path(memcg->css.cgroup, buf, buflen); > - css_put(&memcg->css); > -} > - > -#endif /* CONFIG_MEMCG */ > - > /* > * Trace calls must be in a separate file, as otherwise there's a circular > * dependency between linux/mmap_lock.h and trace/events/mmap_lock.h. > @@ -69,20 +25,20 @@ static void get_mm_memcg_path(struct mm_struct *mm, char *buf, size_t buflen) > > void __mmap_lock_do_trace_start_locking(struct mm_struct *mm, bool write) > { > - TRACE_MMAP_LOCK_EVENT(start_locking, mm, write); > + trace_mmap_lock_start_locking(mm, write); > } > 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_acquire_returned(mm, write, 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_released(mm, write); > } > EXPORT_SYMBOL(__mmap_lock_do_trace_released); > #endif /* CONFIG_TRACING */
diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h index 5502aa8e138e..d82f08cd70cd 100644 --- a/include/linux/memcontrol.h +++ b/include/linux/memcontrol.h @@ -1046,6 +1046,19 @@ static inline void memcg_memory_event_mm(struct mm_struct *mm, void split_page_memcg(struct page *head, int old_order, int new_order); +static inline u64 memcg_id_from_mm(struct mm_struct *mm) +{ + struct mem_cgroup *memcg; + u64 id = 0; + + rcu_read_lock(); + memcg = mem_cgroup_from_task(rcu_dereference(mm->owner)); + if (likely(memcg)) + id = cgroup_id(memcg->css.cgroup); + rcu_read_unlock(); + return id; +} + #else /* CONFIG_MEMCG */ #define MEM_CGROUP_ID_SHIFT 0 @@ -1466,6 +1479,11 @@ void count_memcg_event_mm(struct mm_struct *mm, enum vm_event_item idx) static inline void split_page_memcg(struct page *head, int old_order, int new_order) { } + +static inline u64 memcg_id_from_mm(struct mm_struct *mm) +{ + return 0; +} #endif /* CONFIG_MEMCG */ /* diff --git a/include/trace/events/mmap_lock.h b/include/trace/events/mmap_lock.h index bc2e3ad787b3..5529933d19c5 100644 --- a/include/trace/events/mmap_lock.h +++ b/include/trace/events/mmap_lock.h @@ -5,6 +5,7 @@ #if !defined(_TRACE_MMAP_LOCK_H) || defined(TRACE_HEADER_MULTI_READ) #define _TRACE_MMAP_LOCK_H +#include <linux/memcontrol.h> #include <linux/tracepoint.h> #include <linux/types.h> @@ -12,64 +13,61 @@ struct mm_struct; DECLARE_EVENT_CLASS(mmap_lock, - TP_PROTO(struct mm_struct *mm, const char *memcg_path, bool write), + TP_PROTO(struct mm_struct *mm, bool write), - TP_ARGS(mm, memcg_path, write), + TP_ARGS(mm, write), TP_STRUCT__entry( __field(struct mm_struct *, mm) - __string(memcg_path, memcg_path) + __field(u64, memcg_id) __field(bool, write) ), TP_fast_assign( __entry->mm = mm; - __assign_str(memcg_path); + __entry->memcg_id = memcg_id_from_mm(mm); __entry->write = write; ), TP_printk( - "mm=%p memcg_path=%s write=%s", - __entry->mm, - __get_str(memcg_path), + "mm=%p memcg_id=%llu write=%s", + __entry->mm, __entry->memcg_id, __entry->write ? "true" : "false" ) ); #define DEFINE_MMAP_LOCK_EVENT(name) \ DEFINE_EVENT(mmap_lock, name, \ - TP_PROTO(struct mm_struct *mm, const char *memcg_path, \ - bool write), \ - TP_ARGS(mm, memcg_path, write)) + TP_PROTO(struct mm_struct *mm, bool write), \ + TP_ARGS(mm, write)) DEFINE_MMAP_LOCK_EVENT(mmap_lock_start_locking); DEFINE_MMAP_LOCK_EVENT(mmap_lock_released); TRACE_EVENT(mmap_lock_acquire_returned, - TP_PROTO(struct mm_struct *mm, const char *memcg_path, bool write, - bool success), + TP_PROTO(struct mm_struct *mm, bool write, bool success), - TP_ARGS(mm, memcg_path, write, success), + TP_ARGS(mm, write, success), TP_STRUCT__entry( __field(struct mm_struct *, mm) - __string(memcg_path, memcg_path) + __field(u64, memcg_id) __field(bool, write) __field(bool, success) ), TP_fast_assign( __entry->mm = mm; - __assign_str(memcg_path); + __entry->memcg_id = memcg_id_from_mm(mm); __entry->write = write; __entry->success = success; ), TP_printk( - "mm=%p memcg_path=%s write=%s success=%s", + "mm=%p memcg_id=%llu write=%s success=%s", __entry->mm, - __get_str(memcg_path), + __entry->memcg_id, __entry->write ? "true" : "false", __entry->success ? "true" : "false" ) diff --git a/mm/mmap_lock.c b/mm/mmap_lock.c index f186d57df2c6..e7dbaf96aa17 100644 --- a/mm/mmap_lock.c +++ b/mm/mmap_lock.c @@ -17,51 +17,7 @@ EXPORT_TRACEPOINT_SYMBOL(mmap_lock_start_locking); EXPORT_TRACEPOINT_SYMBOL(mmap_lock_acquire_returned); EXPORT_TRACEPOINT_SYMBOL(mmap_lock_released); -#ifdef CONFIG_MEMCG - -/* - * 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 - -#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 */ - -#define TRACE_MMAP_LOCK_EVENT(type, mm, ...) \ - trace_mmap_lock_##type(mm, "", ##__VA_ARGS__) - -#endif /* CONFIG_MEMCG */ - #ifdef CONFIG_TRACING -#ifdef CONFIG_MEMCG -/* - * Write the given mm_struct's memcg path to a buffer. If the path cannot be - * 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'; - memcg = get_mem_cgroup_from_mm(mm); - if (memcg == NULL) - return; - if (memcg->css.cgroup) - cgroup_path(memcg->css.cgroup, buf, buflen); - css_put(&memcg->css); -} - -#endif /* CONFIG_MEMCG */ - /* * Trace calls must be in a separate file, as otherwise there's a circular * dependency between linux/mmap_lock.h and trace/events/mmap_lock.h. @@ -69,20 +25,20 @@ static void get_mm_memcg_path(struct mm_struct *mm, char *buf, size_t buflen) void __mmap_lock_do_trace_start_locking(struct mm_struct *mm, bool write) { - TRACE_MMAP_LOCK_EVENT(start_locking, mm, write); + trace_mmap_lock_start_locking(mm, write); } 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_acquire_returned(mm, write, 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_released(mm, write); } EXPORT_SYMBOL(__mmap_lock_do_trace_released); #endif /* CONFIG_TRACING */
We are starting to deploy mmap_lock tracepoint monitoring across our fleet and the early results showed that these tracepoints are consuming significant amount of CPUs in kernfs_path_from_node when enabled. It seems like the kernel is trying to resolved the cgroup path in the fast path of the locking code path when the tracepoints are enabled. In addition for some application their metrics are regressing when monitoring is enabled. The cgroup path resolution can be slow and should not be done in the fast path. Most userspace tools, like bpftrace, provides functionality to get the cgroup path from cgroup id, so let's just trace the cgroup id and the users can use better tools to get the path in the slow path. Signed-off-by: Shakeel Butt <shakeel.butt@linux.dev> --- include/linux/memcontrol.h | 18 ++++++++++++ include/trace/events/mmap_lock.h | 32 ++++++++++---------- mm/mmap_lock.c | 50 ++------------------------------ 3 files changed, 36 insertions(+), 64 deletions(-)