Re: [PATCH] vmstat: Keep count of the maximum page reached by the kernel stack

[Pasha Tatashin <pasha.tatashin@soleen.com>]

On Tue, Mar 12, 2024 at 11:34 PM Pasha Tatashin
<pasha.tatashin@soleen.com> wrote:
>
> CONFIG_DEBUG_STACK_USAGE provides a mechanism to know the minimum amount
> of memory that was left in stack. Every time the new anti-record is
> reached a message is printed to the console.
>
> However, this is not useful to know how much each page within stack was
> actually used. Provide a mechanism to count the number of time each
> stack page was reached throughout the live of the stack:
>
>         $ grep kstack /proc/vmstat
>         kstack_page_1 19974
>         kstack_page_2 94
>         kstack_page_3 0
>         kstack_page_4 0
>
> In the above example only out of ~20K threads that ever exited on that
> machine only 94 touched second page of the stack, and none touched
> pages three and four.
>
> Signed-off-by: Pasha Tatashin <pasha.tatashin@soleen.com>
> ---
>  include/linux/sched/task_stack.h | 39 ++++++++++++++++++++++++++++++--
>  include/linux/vm_event_item.h    | 29 ++++++++++++++++++++++++
>  include/linux/vmstat.h           | 16 -------------
>  mm/vmstat.c                      | 11 +++++++++
>  4 files changed, 77 insertions(+), 18 deletions(-)
>
> diff --git a/include/linux/sched/task_stack.h b/include/linux/sched/task_stack.h
> index ccd72b978e1f..7ff7f9997266 100644
> --- a/include/linux/sched/task_stack.h
> +++ b/include/linux/sched/task_stack.h
> @@ -95,9 +95,41 @@ 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 count_kstack_page(int stack_max_page)
> +{
> +       switch (stack_max_page) {
> +       case 1:
> +               this_cpu_inc(vm_event_states.event[KSTACK_PAGE_1]);
> +               break;
> +       case 2:
> +               this_cpu_inc(vm_event_states.event[KSTACK_PAGE_2]);
> +               break;
> +#if THREAD_SIZE >= (4 * PAGE_SIZE)
> +       case 3:
> +               this_cpu_inc(vm_event_states.event[KSTACK_PAGE_3]);
> +               break;
> +       case 4:
> +               this_cpu_inc(vm_event_states.event[KSTACK_PAGE_4]);
> +               break;
> +#endif
> +#if THREAD_SIZE > (4 * PAGE_SIZE)
> +       default:
> +               this_cpu_inc(vm_event_states.event[KSTACK_PAGE_5]);

It should:
this_cpu_inc(vm_event_states.event[KSTACK_PAGE_REST]);

Will fix it in the next version.

> +#endif
> +       }
> +}
> +#else /* !CONFIG_VM_EVENT_COUNTERS */
> +static inline void count_kstack_page(int stack_max_page) {}
> +#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 +140,13 @@ 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
> +       count_kstack_page(((THREAD_SIZE - unused_stack) >> PAGE_SHIFT) + 1);
> +
> +       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..1dbfe47ff048 100644
> --- a/include/linux/vm_event_item.h
> +++ b/include/linux/vm_event_item.h
> @@ -153,10 +153,39 @@ enum vm_event_item { PGPGIN, PGPGOUT, PSWPIN, PSWPOUT,
>                 VMA_LOCK_ABORT,
>                 VMA_LOCK_RETRY,
>                 VMA_LOCK_MISS,
> +#endif
> +#ifdef CONFIG_DEBUG_STACK_USAGE
> +               KSTACK_PAGE_1,
> +               KSTACK_PAGE_2,
> +#if THREAD_SIZE >= (4 * PAGE_SIZE)
> +               KSTACK_PAGE_3,
> +               KSTACK_PAGE_4,
> +#endif
> +#if THREAD_SIZE > (4 * PAGE_SIZE)
> +               KSTACK_PAGE_REST,
> +#endif
>  #endif
>                 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 343906a98d6e..18d4a97d3afd 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 db79935e4a54..737c85689251 100644
> --- a/mm/vmstat.c
> +++ b/mm/vmstat.c
> @@ -1413,6 +1413,17 @@ const char * const vmstat_text[] = {
>         "vma_lock_retry",
>         "vma_lock_miss",
>  #endif
> +#ifdef CONFIG_DEBUG_STACK_USAGE
> +       "kstack_page_1",
> +       "kstack_page_2",
> +#if THREAD_SIZE >= (4 * PAGE_SIZE)
> +       "kstack_page_3",
> +       "kstack_page_4",
> +#endif
> +#if THREAD_SIZE > (4 * PAGE_SIZE)
> +       "kstack_page_rest",
> +#endif
> +#endif
>  #endif /* CONFIG_VM_EVENT_COUNTERS || CONFIG_MEMCG */
>  };
>  #endif /* CONFIG_PROC_FS || CONFIG_SYSFS || CONFIG_NUMA || CONFIG_MEMCG */
> --
> 2.44.0.278.ge034bb2e1d-goog
>