As part of the dynamic kernel stack project, we need to know the amount of data that can be saved by reducing the default kernel stack size [1]. Provide a kernel stack usage histogram to aid in optimizing kernel stack sizes and minimizing memory waste in large-scale environments. The histogram divides stack usage into power-of-two buckets and reports the results in /proc/vmstat. This information is especially valuable in environments with millions of machines, where even small optimizations can have a significant impact. The histogram data is presented in /proc/vmstat with entries like "kstack_1k", "kstack_2k", and so on, indicating the number of threads that exited with stack usage falling within each respective bucket. Example outputs: Intel: $ grep kstack /proc/vmstat kstack_1k 3 kstack_2k 188 kstack_4k 11391 kstack_8k 243 kstack_16k 0 ARM with 64K page_size: $ grep kstack /proc/vmstat kstack_1k 1 kstack_2k 340 kstack_4k 25212 kstack_8k 1659 kstack_16k 0 kstack_32k 0 kstack_64k 0 Note: once the dynamic kernel stack is implemented it will depend on the implementation the usability of this feature: On hardware that supports faults on kernel stacks, we will have other metrics that show the total number of pages allocated for stacks. On hardware where faults are not supported, we will most likely have some optimization where only some threads are extended, and for those, these metrics will still be very useful. [1] https://lwn.net/Articles/974367 Signed-off-by: Pasha Tatashin <pasha.tatashin@xxxxxxxxxx> --- Changelog: v4: - Expanded the commit message as requested by Andrew Morton. include/linux/sched/task_stack.h | 49 ++++++++++++++++++++++++++++++-- include/linux/vm_event_item.h | 42 +++++++++++++++++++++++++++ include/linux/vmstat.h | 16 ----------- mm/vmstat.c | 24 ++++++++++++++++ 4 files changed, 113 insertions(+), 18 deletions(-) diff --git a/include/linux/sched/task_stack.h b/include/linux/sched/task_stack.h index ccd72b978e1f..65e8c9fb7f9b 100644 --- a/include/linux/sched/task_stack.h +++ b/include/linux/sched/task_stack.h @@ -95,9 +95,51 @@ static inline int object_is_on_stack(const void *obj) extern void thread_stack_cache_init(void); #ifdef CONFIG_DEBUG_STACK_USAGE +#ifdef CONFIG_VM_EVENT_COUNTERS +#include <linux/vm_event_item.h> + +/* Count the maximum pages reached in kernel stacks */ +static inline void kstack_histogram(unsigned long used_stack) +{ + if (used_stack <= 1024) + this_cpu_inc(vm_event_states.event[KSTACK_1K]); +#if THREAD_SIZE > 1024 + else if (used_stack <= 2048) + this_cpu_inc(vm_event_states.event[KSTACK_2K]); +#endif +#if THREAD_SIZE > 2048 + else if (used_stack <= 4096) + this_cpu_inc(vm_event_states.event[KSTACK_4K]); +#endif +#if THREAD_SIZE > 4096 + else if (used_stack <= 8192) + this_cpu_inc(vm_event_states.event[KSTACK_8K]); +#endif +#if THREAD_SIZE > 8192 + else if (used_stack <= 16384) + this_cpu_inc(vm_event_states.event[KSTACK_16K]); +#endif +#if THREAD_SIZE > 16384 + else if (used_stack <= 32768) + this_cpu_inc(vm_event_states.event[KSTACK_32K]); +#endif +#if THREAD_SIZE > 32768 + else if (used_stack <= 65536) + this_cpu_inc(vm_event_states.event[KSTACK_64K]); +#endif +#if THREAD_SIZE > 65536 + else + this_cpu_inc(vm_event_states.event[KSTACK_REST]); +#endif +} +#else /* !CONFIG_VM_EVENT_COUNTERS */ +static inline void kstack_histogram(unsigned long used_stack) {} +#endif /* CONFIG_VM_EVENT_COUNTERS */ + static inline unsigned long stack_not_used(struct task_struct *p) { unsigned long *n = end_of_stack(p); + unsigned long unused_stack; do { /* Skip over canary */ # ifdef CONFIG_STACK_GROWSUP @@ -108,10 +150,13 @@ static inline unsigned long stack_not_used(struct task_struct *p) } while (!*n); # ifdef CONFIG_STACK_GROWSUP - return (unsigned long)end_of_stack(p) - (unsigned long)n; + unused_stack = (unsigned long)end_of_stack(p) - (unsigned long)n; # else - return (unsigned long)n - (unsigned long)end_of_stack(p); + unused_stack = (unsigned long)n - (unsigned long)end_of_stack(p); # endif + kstack_histogram(THREAD_SIZE - unused_stack); + + return unused_stack; } #endif extern void set_task_stack_end_magic(struct task_struct *tsk); diff --git a/include/linux/vm_event_item.h b/include/linux/vm_event_item.h index 747943bc8cc2..73fa5fbf33a3 100644 --- a/include/linux/vm_event_item.h +++ b/include/linux/vm_event_item.h @@ -154,9 +154,51 @@ enum vm_event_item { PGPGIN, PGPGOUT, PSWPIN, PSWPOUT, VMA_LOCK_RETRY, VMA_LOCK_MISS, #endif +#ifdef CONFIG_DEBUG_STACK_USAGE + KSTACK_1K, +#if THREAD_SIZE > 1024 + KSTACK_2K, +#endif +#if THREAD_SIZE > 2048 + KSTACK_4K, +#endif +#if THREAD_SIZE > 4096 + KSTACK_8K, +#endif +#if THREAD_SIZE > 8192 + KSTACK_16K, +#endif +#if THREAD_SIZE > 16384 + KSTACK_32K, +#endif +#if THREAD_SIZE > 32768 + KSTACK_64K, +#endif +#if THREAD_SIZE > 65536 + KSTACK_REST, +#endif +#endif /* CONFIG_DEBUG_STACK_USAGE */ NR_VM_EVENT_ITEMS }; +#ifdef CONFIG_VM_EVENT_COUNTERS +/* + * Light weight per cpu counter implementation. + * + * Counters should only be incremented and no critical kernel component + * should rely on the counter values. + * + * Counters are handled completely inline. On many platforms the code + * generated will simply be the increment of a global address. + */ + +struct vm_event_state { + unsigned long event[NR_VM_EVENT_ITEMS]; +}; + +DECLARE_PER_CPU(struct vm_event_state, vm_event_states); +#endif + #ifndef CONFIG_TRANSPARENT_HUGEPAGE #define THP_FILE_ALLOC ({ BUILD_BUG(); 0; }) #define THP_FILE_FALLBACK ({ BUILD_BUG(); 0; }) diff --git a/include/linux/vmstat.h b/include/linux/vmstat.h index 735eae6e272c..131966a4af78 100644 --- a/include/linux/vmstat.h +++ b/include/linux/vmstat.h @@ -41,22 +41,6 @@ enum writeback_stat_item { }; #ifdef CONFIG_VM_EVENT_COUNTERS -/* - * Light weight per cpu counter implementation. - * - * Counters should only be incremented and no critical kernel component - * should rely on the counter values. - * - * Counters are handled completely inline. On many platforms the code - * generated will simply be the increment of a global address. - */ - -struct vm_event_state { - unsigned long event[NR_VM_EVENT_ITEMS]; -}; - -DECLARE_PER_CPU(struct vm_event_state, vm_event_states); - /* * vm counters are allowed to be racy. Use raw_cpu_ops to avoid the * local_irq_disable overhead. diff --git a/mm/vmstat.c b/mm/vmstat.c index 8507c497218b..642d761b557b 100644 --- a/mm/vmstat.c +++ b/mm/vmstat.c @@ -1416,6 +1416,30 @@ const char * const vmstat_text[] = { "vma_lock_retry", "vma_lock_miss", #endif +#ifdef CONFIG_DEBUG_STACK_USAGE + "kstack_1k", +#if THREAD_SIZE > 1024 + "kstack_2k", +#endif +#if THREAD_SIZE > 2048 + "kstack_4k", +#endif +#if THREAD_SIZE > 4096 + "kstack_8k", +#endif +#if THREAD_SIZE > 8192 + "kstack_16k", +#endif +#if THREAD_SIZE > 16384 + "kstack_32k", +#endif +#if THREAD_SIZE > 32768 + "kstack_64k", +#endif +#if THREAD_SIZE > 65536 + "kstack_rest", +#endif +#endif #endif /* CONFIG_VM_EVENT_COUNTERS || CONFIG_MEMCG */ }; #endif /* CONFIG_PROC_FS || CONFIG_SYSFS || CONFIG_NUMA || CONFIG_MEMCG */ -- 2.45.2.1089.g2a221341d9-goog
