Hi Yafang, I've felt a bit stuck on this, as tracepoints alone don't quite address my use case (performance overhead is too high), but I haven't been able to come up with a palatable approach which does. I was planning to conduct an experiment on Google production servers, to provide real-world evidence of why this would be useful. However, the tracepoints alone are still useful, and it sounds like that may be enough for your needs? I'm happy to send a version of this which only adds tracepoints this week. I think at least that subset is uncontroversial. On Tue, Sep 8, 2020 at 4:41 AM Yafang Shao <laoar.shao@xxxxxxxxx> wrote: > > On Fri, Jun 19, 2020 at 6:43 AM Axel Rasmussen <axelrasmussen@xxxxxxxxxx> wrote: > > > > The goal is to be able to collect a latency histogram for contended > > mmap_lock acquisitions. This will be used to diagnose slowness observed > > in production workloads, as well as to measure the effect of upcoming > > mmap_lock optimizations like maple trees and range-based locks. The > > "start_locking" and "lock_released" tracepoints can be used to find out > > which process / call stack was waiting on / holding the lock. > > > > The use of tracepoints with histogram triggers for this purpose was > > recommended here: https://marc.info/?l=linux-mm&m=159076475528369&w=2 > > > > A new Kconfig is added, because this change requires uninlining some > > functions, adding branches, etc., even if the tracepoints aren't enabled > > at runtime. > > > > The semantics of the "acquire_returned" tracepoint are as follows: > > > > - We leverage a new "contended hook" rwsem API so "_trylock" variants > > are called first, and only in the contended case is the trace event > > triggered. This eliminates overhead for the "common" uncontended case. > > > > - "acquire_returned" is triggered even if acquisition fails (e.g. in the > > case of killable acquires). This is so we can see how long we waited, > > even if we didn't get the lock in the end. Whether or not the > > acquisition succeeded is an event parameter. > > > > - The path of the memcg to which the mm_struct belongs is reported in > > the event, so we can have per-memcg historams. But, note that the > > stats are *not* hierarchical; if consumers want a histogram for a > > memcg *and all of its children*, the consumer will need to add up the > > separate per-memcg stats itself. This is to avoid paying the cost of > > traversing a series of memcgs *at record time* (more overhead). > > > > - Bucketing based upon the duration (bucket_{lower,upper}) is done in > > the kernel, as histogram triggers don't have an API to configure such > > a thing at runtime. > > > > Signed-off-by: Axel Rasmussen <axelrasmussen@xxxxxxxxxx> > > --- > > > > Changes since v2: > > - Switched to TRACE_EVENT hist triggers instead of a new hist library. > > - Reduced inlining, as it increased code size with no performance gain. > > - Stopped instrumenting the uncontended case, to reduce overhead. Added > > additional rwsem.h API surface in order to be able to do this. > > > > include/linux/lockdep.h | 47 ++++++ > > include/linux/mmap_lock.h | 27 ++- > > include/linux/rwsem.h | 12 ++ > > include/trace/events/mmap_lock.h | 76 +++++++++ > > kernel/locking/rwsem.c | 64 +++++++ > > mm/Kconfig | 19 +++ > > mm/Makefile | 1 + > > mm/mmap_lock.c | 281 +++++++++++++++++++++++++++++++ > > 8 files changed, 526 insertions(+), 1 deletion(-) > > create mode 100644 include/trace/events/mmap_lock.h > > create mode 100644 mm/mmap_lock.c > > > > diff --git a/include/linux/lockdep.h b/include/linux/lockdep.h > > index 8fce5c98a4b0..6de91046437c 100644 > > --- a/include/linux/lockdep.h > > +++ b/include/linux/lockdep.h > > @@ -590,6 +590,17 @@ do { \ > > lock_acquired(&(_lock)->dep_map, _RET_IP_); \ > > } while (0) > > > > +#define LOCK_CONTENDED_HOOK(_lock, try, lock, pre, post, arg) \ > > +do { \ > > + if (!try(_lock)) { \ > > + lock_contended(&(_lock)->dep_map, _RET_IP_); \ > > + pre(arg); \ > > + lock(_lock); \ > > + post(arg); \ > > + } \ > > + lock_acquired(&(_lock)->dep_map, _RET_IP_); \ > > +} while (0) > > + > > #define LOCK_CONTENDED_RETURN(_lock, try, lock) \ > > ({ \ > > int ____err = 0; \ > > @@ -602,6 +613,21 @@ do { \ > > ____err; \ > > }) > > > > +#define LOCK_CONTENDED_HOOK_RETURN( \ > > + _lock, try, lock, pre, post, arg) \ > > +({ \ > > + int ____err = 0; \ > > + if (!try(_lock)) { \ > > + lock_contended(&(_lock)->dep_map, _RET_IP_); \ > > + pre(arg); \ > > + ____err = lock(_lock); \ > > + post(arg, ____err); \ > > + } \ > > + if (!____err) \ > > + lock_acquired(&(_lock)->dep_map, _RET_IP_); \ > > + ____err; \ > > +}) > > + > > #else /* CONFIG_LOCK_STAT */ > > > > #define lock_contended(lockdep_map, ip) do {} while (0) > > @@ -610,9 +636,30 @@ do { \ > > #define LOCK_CONTENDED(_lock, try, lock) \ > > lock(_lock) > > > > +#define LOCK_CONTENDED_HOOK(_lock, try, lock, pre, post, arg) \ > > +do { \ > > + if (!try(_lock)) { \ > > + pre(arg); \ > > + lock(_lock); \ > > + post(arg); \ > > + } \ > > +} while (0) > > + > > #define LOCK_CONTENDED_RETURN(_lock, try, lock) \ > > lock(_lock) > > > > +#define LOCK_CONTENDED_HOOK_RETURN( \ > > + _lock, try, lock, pre, post, arg) \ > > +({ \ > > + int ____err = 0; \ > > + if (!try(_lock)) { \ > > + pre(arg); \ > > + ____err = lock(_lock); \ > > + post(arg, ____err); \ > > + } \ > > + ____err; \ > > +}) > > + > > #endif /* CONFIG_LOCK_STAT */ > > > > #ifdef CONFIG_LOCKDEP > > diff --git a/include/linux/mmap_lock.h b/include/linux/mmap_lock.h > > index 0707671851a8..1f61f1eac319 100644 > > --- a/include/linux/mmap_lock.h > > +++ b/include/linux/mmap_lock.h > > @@ -1,11 +1,34 @@ > > #ifndef _LINUX_MMAP_LOCK_H > > #define _LINUX_MMAP_LOCK_H > > > > +#include <linux/mm_types.h> > > #include <linux/mmdebug.h> > > +#include <linux/rwsem.h> > > +#include <linux/types.h> > > > > #define MMAP_LOCK_INITIALIZER(name) \ > > .mmap_lock = __RWSEM_INITIALIZER((name).mmap_lock), > > > > +#ifdef CONFIG_MMAP_LOCK_TRACEPOINTS > > + > > +void mmap_init_lock(struct mm_struct *mm); > > +void mmap_write_lock(struct mm_struct *mm); > > +void mmap_write_lock_nested(struct mm_struct *mm, int subclass); > > +int mmap_write_lock_killable(struct mm_struct *mm); > > +bool mmap_write_trylock(struct mm_struct *mm); > > +void mmap_write_unlock(struct mm_struct *mm); > > +void mmap_write_downgrade(struct mm_struct *mm); > > +void mmap_read_lock(struct mm_struct *mm); > > +int mmap_read_lock_killable(struct mm_struct *mm); > > +bool mmap_read_trylock(struct mm_struct *mm); > > +void mmap_read_unlock(struct mm_struct *mm); > > +bool mmap_read_trylock_non_owner(struct mm_struct *mm); > > +void mmap_read_unlock_non_owner(struct mm_struct *mm); > > +void mmap_assert_locked(struct mm_struct *mm); > > +void mmap_assert_write_locked(struct mm_struct *mm); > > + > > +#else /* !CONFIG_MMAP_LOCK_TRACEPOINTS */ > > + > > static inline void mmap_init_lock(struct mm_struct *mm) > > { > > init_rwsem(&mm->mmap_lock); > > @@ -63,7 +86,7 @@ static inline void mmap_read_unlock(struct mm_struct *mm) > > > > static inline bool mmap_read_trylock_non_owner(struct mm_struct *mm) > > { > > - if (down_read_trylock(&mm->mmap_lock)) { > > + if (mmap_read_trylock(mm)) { > > rwsem_release(&mm->mmap_lock.dep_map, _RET_IP_); > > return true; > > } > > @@ -87,4 +110,6 @@ static inline void mmap_assert_write_locked(struct mm_struct *mm) > > VM_BUG_ON_MM(!rwsem_is_locked(&mm->mmap_lock), mm); > > } > > > > +#endif /* CONFIG_MMAP_LOCK_TRACEPOINTS */ > > + > > #endif /* _LINUX_MMAP_LOCK_H */ > > diff --git a/include/linux/rwsem.h b/include/linux/rwsem.h > > index 7e5b2a4eb560..3304a35da4c0 100644 > > --- a/include/linux/rwsem.h > > +++ b/include/linux/rwsem.h > > @@ -123,7 +123,13 @@ static inline int rwsem_is_contended(struct rw_semaphore *sem) > > * lock for reading > > */ > > extern void down_read(struct rw_semaphore *sem); > > +extern void down_read_contended_hook(struct rw_semaphore *sem, > > + void (*pre)(void *), void (*post)(void *), > > + void *arg); > > extern int __must_check down_read_killable(struct rw_semaphore *sem); > > +extern int __must_check > > +down_read_killable_contended_hook(struct rw_semaphore *sem, void (*pre)(void *), > > + void (*post)(void *, int), void *arg); > > > > /* > > * trylock for reading -- returns 1 if successful, 0 if contention > > @@ -134,7 +140,13 @@ extern int down_read_trylock(struct rw_semaphore *sem); > > * lock for writing > > */ > > extern void down_write(struct rw_semaphore *sem); > > +extern void down_write_contended_hook(struct rw_semaphore *sem, > > + void (*pre)(void *), void (*post)(void *), > > + void *arg); > > extern int __must_check down_write_killable(struct rw_semaphore *sem); > > +extern int __must_check down_write_killable_contended_hook( > > + struct rw_semaphore *sem, void (*pre)(void *), > > + void (*post)(void *, int), void *arg); > > > > /* > > * trylock for writing -- returns 1 if successful, 0 if contention > > diff --git a/include/trace/events/mmap_lock.h b/include/trace/events/mmap_lock.h > > new file mode 100644 > > index 000000000000..d1d4c83b848e > > --- /dev/null > > +++ b/include/trace/events/mmap_lock.h > > @@ -0,0 +1,76 @@ > > +/* SPDX-License-Identifier: GPL-2.0 */ > > +#undef TRACE_SYSTEM > > +#define TRACE_SYSTEM mmap_lock > > + > > +#if !defined(_TRACE_MMAP_LOCK_H) || defined(TRACE_HEADER_MULTI_READ) > > +#define _TRACE_MMAP_LOCK_H > > + > > +#include <linux/tracepoint.h> > > +#include <linux/types.h> > > + > > +struct mm_struct; > > + > > +DECLARE_EVENT_CLASS( > > + mmap_lock_template, > > + > > + TP_PROTO(struct mm_struct *mm, const char *memcg_path, u64 duration, > > + bool success, u64 bucket_lower, u64 bucket_upper), > > + > > + TP_ARGS(mm, memcg_path, duration, success, bucket_lower, bucket_upper), > > + > > + TP_STRUCT__entry( > > + __field(struct mm_struct *, mm) > > + __string(memcg_path, memcg_path) > > + __field(u64, duration) > > + __field(bool, success) > > + __field(u64, bucket_lower) > > + __field(u64, bucket_upper) > > + ), > > + > > + TP_fast_assign( > > + __entry->mm = mm; > > + __assign_str(memcg_path, memcg_path); > > + __entry->duration = duration; > > + __entry->success = success; > > + __entry->bucket_lower = bucket_lower; > > + __entry->bucket_upper = bucket_upper; > > + ), > > + > > + TP_printk( > > + "mm=%p memcg_path=%s duration=%llu success=%s bucket=[%llu, %llu]\n", > > + __entry->mm, > > + __get_str(memcg_path), > > + __entry->duration, > > + __entry->success ? "true" : "false", > > + __entry->bucket_lower, > > + __entry->bucket_upper) > > + ); > > + > > +DEFINE_EVENT(mmap_lock_template, mmap_lock_start_locking, > > + > > + TP_PROTO(struct mm_struct *mm, const char *memcg_path, u64 duration, > > + bool success, u64 bucket_lower, u64 bucket_upper), > > + > > + TP_ARGS(mm, memcg_path, duration, success, bucket_lower, bucket_upper) > > +); > > + > > +DEFINE_EVENT(mmap_lock_template, mmap_lock_acquire_returned, > > + > > + TP_PROTO(struct mm_struct *mm, const char *memcg_path, u64 duration, > > + bool success, u64 bucket_lower, u64 bucket_upper), > > + > > + TP_ARGS(mm, memcg_path, duration, success, bucket_lower, bucket_upper) > > +); > > + > > +DEFINE_EVENT(mmap_lock_template, mmap_lock_released, > > + > > + TP_PROTO(struct mm_struct *mm, const char *memcg_path, u64 duration, > > + bool success, u64 bucket_lower, u64 bucket_upper), > > + > > + TP_ARGS(mm, memcg_path, duration, success, bucket_lower, bucket_upper) > > +); > > + > > +#endif /* _TRACE_MMAP_LOCK_H */ > > + > > +/* This part must be outside protection */ > > +#include <trace/define_trace.h> > > diff --git a/kernel/locking/rwsem.c b/kernel/locking/rwsem.c > > index f11b9bd3431d..6aabea1cbc5d 100644 > > --- a/kernel/locking/rwsem.c > > +++ b/kernel/locking/rwsem.c > > @@ -1495,6 +1495,20 @@ void __sched down_read(struct rw_semaphore *sem) > > } > > EXPORT_SYMBOL(down_read); > > > > +/* > > + * lock for reading > > + */ > > +void __sched down_read_contended_hook(struct rw_semaphore *sem, > > + void (*pre)(void *), > > + void (*post)(void *), void *arg) > > +{ > > + might_sleep(); > > + rwsem_acquire_read(&sem->dep_map, 0, 0, _RET_IP_); > > + LOCK_CONTENDED_HOOK(sem, __down_read_trylock, __down_read, pre, post, > > + arg); > > +} > > +EXPORT_SYMBOL(down_read_contended_hook); > > + > > int __sched down_read_killable(struct rw_semaphore *sem) > > { > > might_sleep(); > > @@ -1509,6 +1523,24 @@ int __sched down_read_killable(struct rw_semaphore *sem) > > } > > EXPORT_SYMBOL(down_read_killable); > > > > +int __sched down_read_killable_contended_hook(struct rw_semaphore *sem, > > + void (*pre)(void *), > > + void (*post)(void *, int), > > + void *arg) > > +{ > > + might_sleep(); > > + rwsem_acquire_read(&sem->dep_map, 0, 0, _RET_IP_); > > + > > + if (LOCK_CONTENDED_HOOK_RETURN(sem, __down_read_trylock, > > + __down_read_killable, pre, post, arg)) { > > + rwsem_release(&sem->dep_map, _RET_IP_); > > + return -EINTR; > > + } > > + > > + return 0; > > +} > > +EXPORT_SYMBOL(down_read_killable_contended_hook); > > + > > /* > > * trylock for reading -- returns 1 if successful, 0 if contention > > */ > > @@ -1533,6 +1565,20 @@ void __sched down_write(struct rw_semaphore *sem) > > } > > EXPORT_SYMBOL(down_write); > > > > +/* > > + * lock for writing > > + */ > > +void __sched down_write_contended_hook(struct rw_semaphore *sem, > > + void (*pre)(void *), > > + void (*post)(void *), void *arg) > > +{ > > + might_sleep(); > > + rwsem_acquire(&sem->dep_map, 0, 0, _RET_IP_); > > + LOCK_CONTENDED_HOOK(sem, __down_write_trylock, __down_write, pre, post, > > + arg); > > +} > > +EXPORT_SYMBOL(down_write_contended_hook); > > + > > /* > > * lock for writing > > */ > > @@ -1551,6 +1597,24 @@ int __sched down_write_killable(struct rw_semaphore *sem) > > } > > EXPORT_SYMBOL(down_write_killable); > > > > +int __sched down_write_killable_contended_hook(struct rw_semaphore *sem, > > + void (*pre)(void *), > > + void (*post)(void *, int), > > + void *arg) > > +{ > > + might_sleep(); > > + rwsem_acquire_read(&sem->dep_map, 0, 0, _RET_IP_); > > + > > + if (LOCK_CONTENDED_HOOK_RETURN(sem, __down_write_trylock, > > + __down_write_killable, pre, post, arg)) { > > + rwsem_release(&sem->dep_map, _RET_IP_); > > + return -EINTR; > > + } > > + > > + return 0; > > +} > > +EXPORT_SYMBOL(down_write_killable_contended_hook); > > + > > /* > > * trylock for writing -- returns 1 if successful, 0 if contention > > */ > > diff --git a/mm/Kconfig b/mm/Kconfig > > index f2104cc0d35c..a88b44ff46e2 100644 > > --- a/mm/Kconfig > > +++ b/mm/Kconfig > > @@ -822,6 +822,25 @@ config DEVICE_PRIVATE > > config FRAME_VECTOR > > bool > > > > +config MMAP_LOCK_TRACEPOINTS > > + bool "mmap_lock tracepoints" > > + select HISTOGRAM > > + select HIST_TRIGGERS > > + default n > > + > > + help > > + Enable kernel tracepoints around mmap_lock acquisition. These can be > > + enabled / disabled at runtime, although note there is a small amount > > + of overhead even before the tracepoints are runtime-enabled. When > > + histogram triggers are configured at runtime, less than 1% overhead > > + is added to typical workloads. > > + > > + This option selects CONFIG_HIST_TRIGGERS, since one of the main > > + purposes of this feature is to allow lock acquisition latency > > + histograms to be collected. > > + > > + If unsure, say "N". > > + > > config ARCH_USES_HIGH_VMA_FLAGS > > bool > > config ARCH_HAS_PKEYS > > diff --git a/mm/Makefile b/mm/Makefile > > index 6e9d46b2efc9..14860f7b9984 100644 > > --- a/mm/Makefile > > +++ b/mm/Makefile > > @@ -121,3 +121,4 @@ obj-$(CONFIG_MEMFD_CREATE) += memfd.o > > obj-$(CONFIG_MAPPING_DIRTY_HELPERS) += mapping_dirty_helpers.o > > obj-$(CONFIG_PTDUMP_CORE) += ptdump.o > > obj-$(CONFIG_PAGE_REPORTING) += page_reporting.o > > +obj-$(CONFIG_MMAP_LOCK_TRACEPOINTS) += mmap_lock.o > > diff --git a/mm/mmap_lock.c b/mm/mmap_lock.c > > new file mode 100644 > > index 000000000000..d0734d6325ea > > --- /dev/null > > +++ b/mm/mmap_lock.c > > @@ -0,0 +1,281 @@ > > +// SPDX-License-Identifier: GPL-2.0 > > +#define CREATE_TRACE_POINTS > > +#include <trace/events/mmap_lock.h> > > + > > +#include <linux/cgroup.h> > > +#include <linux/kernel.h> > > +#include <linux/memcontrol.h> > > +#include <linux/mmap_lock.h> > > +#include <linux/percpu.h> > > +#include <linux/smp.h> > > +#include <linux/trace_events.h> > > +#include <linux/sched/clock.h> > > + > > +static const u64 mmap_lock_buckets[] = { > > + 250, /* 250 ns */ > > + 375, /* 375 ns */ > > + 500, /* 500 ns */ > > + 1000, /* 1 us */ > > + 10000, /* 10 us */ > > + 100000, /* 100 us */ > > + 500000, /* 500 us */ > > + 1000000, /* 1 ms */ > > + 5000000, /* 5 ms */ > > + 10000000, /* 10 ms */ > > + 50000000, /* 50 ms */ > > + 100000000, /* 100 ms */ > > + 500000000, /* 500 ms */ > > + 1000000000, /* 1 s */ > > + 5000000000UL, /* 5 s */ > > + 10000000000UL, /* 10 s */ > > + ~0 /* > 10s */ > > +}; > > + > > +static int find_bucket(u64 duration) > > +{ > > + int i, lower, upper; > > + > > + lower = 0; > > + upper = ARRAY_SIZE(mmap_lock_buckets) - 1; > > + while (lower < upper) { > > + /* Can't realistically overflow, number of buckets < 2**63. */ > > + i = (lower + upper) / 2; > > + if (duration <= mmap_lock_buckets[i]) > > + upper = i; > > + else > > + lower = i + 1; > > + } > > + return upper; > > +} > > + > > +#ifdef CONFIG_MEMCG > > + > > +DEFINE_PER_CPU(char[MAX_FILTER_STR_VAL], trace_memcg_path); > > + > > +/* > > + * Write the given mm_struct's memcg path to a percpu buffer, and return a > > + * pointer to it. If the path cannot be determined, the buffer will contain the > > + * empty string. > > + * > > + * Note: buffers are allocated per-cpu to avoid locking, so preemption must be > > + * disabled by the caller before calling us, and re-enabled only after the > > + * caller is done with the pointer. > > + */ > > +static const char *get_mm_memcg_path(struct mm_struct *mm) > > +{ > > + struct mem_cgroup *memcg = get_mem_cgroup_from_mm(mm); > > + > > + if (memcg != NULL && likely(memcg->css.cgroup != NULL)) { > > + char *buf = this_cpu_ptr(trace_memcg_path); > > + > > + cgroup_path(memcg->css.cgroup, buf, MAX_FILTER_STR_VAL); > > + return buf; > > + } > > + return ""; > > +} > > + > > +#define TRACE_MMAP_LOCK_EVENT(type, mm, ...) \ > > + do { \ > > + if (trace_mmap_lock_##type##_enabled()) { \ > > + get_cpu(); \ > > + trace_mmap_lock_##type(mm, get_mm_memcg_path(mm), \ > > + ##__VA_ARGS__); \ > > + put_cpu(); \ > > + } \ > > + } while (0) > > + > > +#else /* CONFIG_MEMCG */ > > + > > +#define TRACE_MMAP_LOCK_EVENT(type, mm, ...) \ > > + trace_mmap_lock_##type(mm, "", ##__VA_ARGS__) > > + > > +#endif /* CONFIG_MEMCG */ > > + > > +/* > > + * Trace calls must be in a separate file, as otherwise there's a cirtuclar > > + * dependency between linux/mmap_lock.h and trace/events/mmap_lock.h. > > + */ > > + > > +static void trace_start_locking(struct mm_struct *mm) > > +{ > > + TRACE_MMAP_LOCK_EVENT(start_locking, mm, 0, true, 0, > > + mmap_lock_buckets[0]); > > +} > > + > > +static void trace_acquire_returned(struct mm_struct *mm, u64 start_time_ns, > > + bool success) > > +{ > > + u64 duration = sched_clock() - start_time_ns; > > + int i = find_bucket(duration); > > + > > + TRACE_MMAP_LOCK_EVENT(acquire_returned, mm, duration, success, > > + i > 0 ? mmap_lock_buckets[i - 1] + 1 : 0, > > + mmap_lock_buckets[i]); > > +} > > + > > +static void trace_released(struct mm_struct *mm) > > +{ > > + TRACE_MMAP_LOCK_EVENT(released, mm, 0, true, 0, mmap_lock_buckets[0]); > > +} > > + > > +struct trace_context { > > + struct mm_struct *mm; > > + u64 start_time_ns; > > +}; > > + > > +static inline void trace_pre(void *c) > > +{ > > + ((struct trace_context *) c)->start_time_ns = sched_clock(); > > +} > > + > > +static void trace_post_return(void *c, int ret) > > +{ > > + struct trace_context *context = (struct trace_context *)c; > > + > > + trace_acquire_returned(context->mm, context->start_time_ns, ret == 0); > > +} > > + > > +static inline void trace_post(void *c) > > +{ > > + trace_post_return(c, 0); > > +} > > + > > +static inline bool trylock_impl(struct mm_struct *mm, > > + int (*trylock)(struct rw_semaphore *)) > > +{ > > + trace_start_locking(mm); > > + return trylock(&mm->mmap_lock) != 0; > > +} > > + > > +static inline void lock_impl(struct mm_struct *mm, > > + void (*lock)(struct rw_semaphore *, > > + void (*)(void *), void (*)(void *), > > + void *)) > > +{ > > + struct trace_context context = { .mm = mm, .start_time_ns = 0 }; > > + > > + trace_start_locking(mm); > > + lock(&mm->mmap_lock, trace_pre, trace_post, &context); > > +} > > + > > +static inline int lock_return_impl(struct mm_struct *mm, > > + int (*lock)(struct rw_semaphore *, > > + void (*)(void *), > > + void (*)(void *, int), void *)) > > +{ > > + struct trace_context context = { .mm = mm, .start_time_ns = 0 }; > > + > > + trace_start_locking(mm); > > + return lock(&mm->mmap_lock, trace_pre, trace_post_return, &context); > > +} > > + > > +void mmap_init_lock(struct mm_struct *mm) > > +{ > > + init_rwsem(&mm->mmap_lock); > > +} > > +EXPORT_SYMBOL_GPL(mmap_init_lock); > > + > > +void mmap_write_lock(struct mm_struct *mm) > > +{ > > + lock_impl(mm, down_write_contended_hook); > > +} > > +EXPORT_SYMBOL_GPL(mmap_write_lock); > > + > > +void mmap_write_lock_nested(struct mm_struct *mm, int subclass) > > +{ > > + /* > > + * Unlike other functions, we don't need the contended hook API here. > > + * This is because we don't care about breaking out the {un,}contended > > + * cases. > > + * > > + * This function is only called once on fork (nowhere else), so 1) > > + * performance isn't as important, and 2) we expect to never experience > > + * contention. > > + */ > > + u64 start_time_ns = sched_clock(); > > + > > + down_write_nested(&mm->mmap_lock, subclass); > > + trace_acquire_returned(mm, start_time_ns, true); > > +} > > +EXPORT_SYMBOL_GPL(mmap_write_lock_nested); > > + > > +int mmap_write_lock_killable(struct mm_struct *mm) > > +{ > > + return lock_return_impl(mm, down_write_killable_contended_hook); > > +} > > +EXPORT_SYMBOL_GPL(mmap_write_lock_killable); > > + > > +bool mmap_write_trylock(struct mm_struct *mm) > > +{ > > + return trylock_impl(mm, down_write_trylock); > > +} > > +EXPORT_SYMBOL_GPL(mmap_write_trylock); > > + > > +void mmap_write_unlock(struct mm_struct *mm) > > +{ > > + up_write(&mm->mmap_lock); > > + trace_released(mm); > > +} > > +EXPORT_SYMBOL_GPL(mmap_write_unlock); > > + > > +void mmap_write_downgrade(struct mm_struct *mm) > > +{ > > + downgrade_write(&mm->mmap_lock); > > +} > > +EXPORT_SYMBOL_GPL(mmap_write_downgrade); > > + > > +void mmap_read_lock(struct mm_struct *mm) > > +{ > > + lock_impl(mm, down_read_contended_hook); > > +} > > +EXPORT_SYMBOL_GPL(mmap_read_lock); > > + > > +int mmap_read_lock_killable(struct mm_struct *mm) > > +{ > > + return lock_return_impl(mm, down_read_killable_contended_hook); > > +} > > +EXPORT_SYMBOL_GPL(mmap_read_lock_killable); > > + > > +bool mmap_read_trylock(struct mm_struct *mm) > > +{ > > + return trylock_impl(mm, down_read_trylock); > > +} > > +EXPORT_SYMBOL_GPL(mmap_read_trylock); > > + > > +void mmap_read_unlock(struct mm_struct *mm) > > +{ > > + up_read(&mm->mmap_lock); > > + trace_released(mm); > > +} > > +EXPORT_SYMBOL_GPL(mmap_read_unlock); > > + > > +bool mmap_read_trylock_non_owner(struct mm_struct *mm) > > +{ > > + if (trylock_impl(mm, down_read_trylock)) { > > + rwsem_release(&mm->mmap_lock.dep_map, _RET_IP_); > > + return true; > > + } > > + return false; > > +} > > +EXPORT_SYMBOL_GPL(mmap_read_trylock_non_owner); > > + > > +void mmap_read_unlock_non_owner(struct mm_struct *mm) > > +{ > > + up_read_non_owner(&mm->mmap_lock); > > + trace_released(mm); > > +} > > +EXPORT_SYMBOL_GPL(mmap_read_unlock_non_owner); > > + > > +void mmap_assert_locked(struct mm_struct *mm) > > +{ > > + lockdep_assert_held(&mm->mmap_lock); > > + VM_BUG_ON_MM(!rwsem_is_locked(&mm->mmap_lock), mm); > > +} > > +EXPORT_SYMBOL_GPL(mmap_assert_locked); > > + > > +void mmap_assert_write_locked(struct mm_struct *mm) > > +{ > > + lockdep_assert_held_write(&mm->mmap_lock); > > + VM_BUG_ON_MM(!rwsem_is_locked(&mm->mmap_lock), mm); > > +} > > +EXPORT_SYMBOL_GPL(mmap_assert_write_locked); > > -- > > 2.27.0.111.gc72c7da667-goog > > > > > > Hi Axel, > > Any updates on this patchset ? > > I think adding tracepoints to trace the mmap_lock would be helpful to > us, which can help us identify which one holds the mmap_lock too long > and why it takes too long. > > > -- > Thanks > Yafang
