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> Reviewed-by: Kent Overstreet <kent.overstreet@xxxxxxxxx> --- include/linux/vm_event_item.h | 24 ++++++++++++++++++++++ kernel/exit.c | 38 +++++++++++++++++++++++++++++++++++ mm/vmstat.c | 24 ++++++++++++++++++++++ 3 files changed, 86 insertions(+) diff --git a/include/linux/vm_event_item.h b/include/linux/vm_event_item.h index 747943bc8cc2..37ad1c16367a 100644 --- a/include/linux/vm_event_item.h +++ b/include/linux/vm_event_item.h @@ -154,6 +154,30 @@ 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 }; diff --git a/kernel/exit.c b/kernel/exit.c index 7430852a8571..64bfc2bae55b 100644 --- a/kernel/exit.c +++ b/kernel/exit.c @@ -778,6 +778,43 @@ static void exit_notify(struct task_struct *tsk, int group_dead) } #ifdef CONFIG_DEBUG_STACK_USAGE +/* Count the maximum pages reached in kernel stacks */ +static inline void kstack_histogram(unsigned long used_stack) +{ +#ifdef CONFIG_VM_EVENT_COUNTERS + if (used_stack <= 1024) + count_vm_event(KSTACK_1K); +#if THREAD_SIZE > 1024 + else if (used_stack <= 2048) + count_vm_event(KSTACK_2K); +#endif +#if THREAD_SIZE > 2048 + else if (used_stack <= 4096) + count_vm_event(KSTACK_4K); +#endif +#if THREAD_SIZE > 4096 + else if (used_stack <= 8192) + count_vm_event(KSTACK_8K); +#endif +#if THREAD_SIZE > 8192 + else if (used_stack <= 16384) + count_vm_event(KSTACK_16K); +#endif +#if THREAD_SIZE > 16384 + else if (used_stack <= 32768) + count_vm_event(KSTACK_32K); +#endif +#if THREAD_SIZE > 32768 + else if (used_stack <= 65536) + count_vm_event(KSTACK_64K); +#endif +#if THREAD_SIZE > 65536 + else + count_vm_event(KSTACK_REST); +#endif +#endif /* CONFIG_VM_EVENT_COUNTERS */ +} + static void check_stack_usage(void) { static DEFINE_SPINLOCK(low_water_lock); @@ -785,6 +822,7 @@ static void check_stack_usage(void) unsigned long free; free = stack_not_used(current); + kstack_histogram(THREAD_SIZE - free); if (free >= lowest_to_date) return; diff --git a/mm/vmstat.c b/mm/vmstat.c index 73d791d1caad..6e3347789eb2 100644 --- a/mm/vmstat.c +++ b/mm/vmstat.c @@ -1417,6 +1417,30 @@ 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
