Re: [PATCH RFC 1/2] stackdepot: add stats counters exported via debugfs

[Andrey Konovalov <andreyknvl@gmail.com>]

On Mon, Jan 15, 2024 at 10:27 AM Marco Elver <elver@google.com> wrote:
>
> Add a few basic stats counters for stack depot that can be used to derive if
> stack depot is working as intended. This is a snapshot of the new stats after
> booting a system with a KASAN-enabled kernel:
>
>  $ cat /sys/kernel/debug/stackdepot/stats
>  pools: 838
>  allocations: 29861
>  frees: 6561
>  in_use: 23300
>  freelist_size: 1840
>
> Generally, "pools" should be well below the max; once the system is booted,
> "in_use" should remain relatively steady.
>
> Signed-off-by: Marco Elver <elver@google.com>
> ---
>  lib/stackdepot.c | 53 ++++++++++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 53 insertions(+)
>
> diff --git a/lib/stackdepot.c b/lib/stackdepot.c
> index a0be5d05c7f0..80a8ca24ccc8 100644
> --- a/lib/stackdepot.c
> +++ b/lib/stackdepot.c
> @@ -14,6 +14,7 @@
>
>  #define pr_fmt(fmt) "stackdepot: " fmt
>
> +#include <linux/debugfs.h>
>  #include <linux/gfp.h>
>  #include <linux/jhash.h>
>  #include <linux/kernel.h>
> @@ -115,6 +116,23 @@ static bool new_pool_required = true;
>  /* Lock that protects the variables above. */
>  static DEFINE_RWLOCK(pool_rwlock);
>
> +/* Statistics counters for debugfs. */
> +enum depot_counter_id {
> +       DEPOT_COUNTER_ALLOCS,
> +       DEPOT_COUNTER_FREES,
> +       DEPOT_COUNTER_INUSE,
> +       DEPOT_COUNTER_FREELIST_SIZE,
> +       DEPOT_COUNTER_COUNT,
> +};
> +static long counters[DEPOT_COUNTER_COUNT];
> +static const char *const counter_names[] = {
> +       [DEPOT_COUNTER_ALLOCS]          = "allocations",
> +       [DEPOT_COUNTER_FREES]           = "frees",
> +       [DEPOT_COUNTER_INUSE]           = "in_use",
> +       [DEPOT_COUNTER_FREELIST_SIZE]   = "freelist_size",
> +};
> +static_assert(ARRAY_SIZE(counter_names) == DEPOT_COUNTER_COUNT);
> +
>  static int __init disable_stack_depot(char *str)
>  {
>         return kstrtobool(str, &stack_depot_disabled);
> @@ -277,6 +295,7 @@ static void depot_init_pool(void *pool)
>                 stack->handle.extra = 0;
>
>                 list_add(&stack->list, &free_stacks);
> +               counters[DEPOT_COUNTER_FREELIST_SIZE]++;
>         }
>
>         /* Save reference to the pool to be used by depot_fetch_stack(). */
> @@ -376,6 +395,7 @@ depot_alloc_stack(unsigned long *entries, int size, u32 hash, void **prealloc)
>         /* Get and unlink the first entry from the freelist. */
>         stack = list_first_entry(&free_stacks, struct stack_record, list);
>         list_del(&stack->list);
> +       counters[DEPOT_COUNTER_FREELIST_SIZE]--;
>
>         /* Limit number of saved frames to CONFIG_STACKDEPOT_MAX_FRAMES. */
>         if (size > CONFIG_STACKDEPOT_MAX_FRAMES)
> @@ -394,6 +414,8 @@ depot_alloc_stack(unsigned long *entries, int size, u32 hash, void **prealloc)
>          */
>         kmsan_unpoison_memory(stack, DEPOT_STACK_RECORD_SIZE);
>
> +       counters[DEPOT_COUNTER_ALLOCS]++;
> +       counters[DEPOT_COUNTER_INUSE]++;
>         return stack;
>  }
>
> @@ -426,6 +448,10 @@ static void depot_free_stack(struct stack_record *stack)
>         lockdep_assert_held_write(&pool_rwlock);
>
>         list_add(&stack->list, &free_stacks);
> +
> +       counters[DEPOT_COUNTER_FREELIST_SIZE]++;
> +       counters[DEPOT_COUNTER_FREES]++;
> +       counters[DEPOT_COUNTER_INUSE]--;
>  }
>
>  /* Calculates the hash for a stack. */
> @@ -690,3 +716,30 @@ unsigned int stack_depot_get_extra_bits(depot_stack_handle_t handle)
>         return parts.extra;
>  }
>  EXPORT_SYMBOL(stack_depot_get_extra_bits);
> +
> +static int stats_show(struct seq_file *seq, void *v)
> +{
> +       /*
> +        * data race ok: These are just statistics counters, and approximate
> +        * statistics are ok for debugging.
> +        */
> +       seq_printf(seq, "pools: %d\n", data_race(pools_num));
> +       for (int i = 0; i < DEPOT_COUNTER_COUNT; i++)
> +               seq_printf(seq, "%s: %ld\n", counter_names[i], data_race(counters[i]));
> +
> +       return 0;
> +}
> +DEFINE_SHOW_ATTRIBUTE(stats);
> +
> +static int depot_debugfs_init(void)
> +{
> +       struct dentry *dir;
> +
> +       if (stack_depot_disabled)
> +               return 0;
> +
> +       dir = debugfs_create_dir("stackdepot", NULL);
> +       debugfs_create_file("stats", 0444, dir, NULL, &stats_fops);
> +       return 0;
> +}
> +late_initcall(depot_debugfs_init);
> --
> 2.43.0.275.g3460e3d667-goog
>

Reviewed-by: Andrey Konovalov <andreyknvl@gmail.com>