Re: [PATCH v3] lib: stackdepot: Add support to configure STACK_HASH_SIZE

[Dmitry Vyukov]

On Thu, Dec 10, 2020 at 6:04 AM <vjitta@xxxxxxxxxxxxxx> wrote:
>
> From: Yogesh Lal <ylal@xxxxxxxxxxxxxx>
>
> Add a kernel parameter stack_hash_order to configure STACK_HASH_SIZE.
>
> Aim is to have configurable value for STACK_HASH_SIZE, so that one
> can configure it depending on usecase there by reducing the static
> memory overhead.
>
> One example is of Page Owner, default value of STACK_HASH_SIZE lead
> stack depot to consume 8MB of static memory. Making it configurable
> and use lower value helps to enable features like CONFIG_PAGE_OWNER
> without any significant overhead.
>
> Suggested-by: Minchan Kim <minchan@xxxxxxxxxx>
> Signed-off-by: Yogesh Lal <ylal@xxxxxxxxxxxxxx>
> Signed-off-by: Vijayanand Jitta <vjitta@xxxxxxxxxxxxxx>
> ---
>  lib/stackdepot.c | 31 +++++++++++++++++++++++++++----
>  1 file changed, 27 insertions(+), 4 deletions(-)
>
> diff --git a/lib/stackdepot.c b/lib/stackdepot.c
> index 81c69c0..e0eebfd 100644
> --- a/lib/stackdepot.c
> +++ b/lib/stackdepot.c
> @@ -30,6 +30,7 @@
>  #include <linux/stackdepot.h>
>  #include <linux/string.h>
>  #include <linux/types.h>
> +#include <linux/vmalloc.h>
>
>  #define DEPOT_STACK_BITS (sizeof(depot_stack_handle_t) * 8)
>
> @@ -141,14 +142,36 @@ static struct stack_record *depot_alloc_stack(unsigned long *entries, int size,
>         return stack;
>  }
>
> -#define STACK_HASH_ORDER 20
> -#define STACK_HASH_SIZE (1L << STACK_HASH_ORDER)
> +#define MAX_STACK_HASH_ORDER 20
> +#define MAX_STACK_HASH_SIZE (1L << MAX_STACK_HASH_ORDER)
> +#define STACK_HASH_SIZE (1L << stack_hash_order)
>  #define STACK_HASH_MASK (STACK_HASH_SIZE - 1)
>  #define STACK_HASH_SEED 0x9747b28c
>
> -static struct stack_record *stack_table[STACK_HASH_SIZE] = {
> -       [0 ...  STACK_HASH_SIZE - 1] = NULL
> +static unsigned int stack_hash_order = 20;
> +static struct stack_record *stack_table_def[MAX_STACK_HASH_SIZE] __initdata = {
> +       [0 ...  MAX_STACK_HASH_SIZE - 1] = NULL
>  };
> +static struct stack_record **stack_table __refdata = stack_table_def;
> +
> +static int __init setup_stack_hash_order(char *str)
> +{
> +       kstrtouint(str, 0, &stack_hash_order);
> +       if (stack_hash_order > MAX_STACK_HASH_ORDER)
> +               stack_hash_order = MAX_STACK_HASH_ORDER;
> +       return 0;
> +}
> +early_param("stack_hash_order", setup_stack_hash_order);
> +
> +static int __init init_stackdepot(void)
> +{
> +       size_t size = (STACK_HASH_SIZE * sizeof(struct stack_record *));
> +
> +       stack_table = vmalloc(size);
> +       memcpy(stack_table, stack_table_def, size);

Can interrupts happen at this point in time? If yes, they can
use/modify stack_table_def concurrently.

> +       return 0;
> +}
> +early_initcall(init_stackdepot);
>
>  /* Calculate hash for a stack */
>  static inline u32 hash_stack(unsigned long *entries, unsigned int size)
> --
> 2.7.4
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