linux-kernel - Re: [PATCH v8 4/5] mm,page_owner: Filter out stacks by a threshold

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Date: Tue, 13 Feb 2024 09:41:02 +0100
From: Marco Elver <elver@...gle.com>
To: Oscar Salvador <osalvador@...e.de>
Cc: Andrew Morton <akpm@...ux-foundation.org>, linux-kernel@...r.kernel.org, 
	linux-mm@...ck.org, Michal Hocko <mhocko@...e.com>, Vlastimil Babka <vbabka@...e.cz>, 
	Andrey Konovalov <andreyknvl@...il.com>, Alexander Potapenko <glider@...gle.com>
Subject: Re: [PATCH v8 4/5] mm,page_owner: Filter out stacks by a threshold

On Mon, 12 Feb 2024 at 23:29, Oscar Salvador <osalvador@...e.de> wrote:
>
> We want to be able to filter out the stacks based on a threshold we can
> can tune.
> By writing to 'set_threshold' file, we can adjust the threshold value.
>
> Signed-off-by: Oscar Salvador <osalvador@...e.de>
> ---
>  mm/page_owner.c | 24 ++++++++++++++++++++++--
>  1 file changed, 22 insertions(+), 2 deletions(-)
>
> diff --git a/mm/page_owner.c b/mm/page_owner.c
> index 3e4b7cd7c8f8..c4f9e5506e93 100644
> --- a/mm/page_owner.c
> +++ b/mm/page_owner.c
> @@ -832,15 +832,18 @@ static void *stack_next(struct seq_file *m, void *v, loff_t *ppos)
>         return stack;
>  }
>
> +static unsigned long page_owner_stack_threshold;
> +
>  static int stack_print(struct seq_file *m, void *v)
>  {
>         char *buf;
>         int ret = 0;
>         struct stack *stack = v;
>         struct stack_record *stack_record = stack->stack_record;
> +       int stack_count = refcount_read(&stack_record->count);
>
>         if (!stack_record->size || stack_record->size < 0 ||
> -           refcount_read(&stack_record->count) < 2)
> +           stack_count < 2 || stack_count < page_owner_stack_threshold)
>                 return 0;
>
>         buf = kzalloc(PAGE_SIZE, GFP_KERNEL);
> @@ -851,7 +854,7 @@ static int stack_print(struct seq_file *m, void *v)
>                 goto out;
>
>         scnprintf(buf + ret, PAGE_SIZE - ret, "stack_count: %d\n\n",
> -                 refcount_read(&stack_record->count));
> +                 stack_count);
>
>         seq_printf(m, buf);
>         seq_puts(m, "\n\n");
> @@ -884,6 +887,21 @@ static const struct file_operations page_owner_stack_operations = {
>         .release        = seq_release,
>  };
>
> +static int page_owner_threshold_get(void *data, u64 *val)
> +{
> +       *val = page_owner_stack_threshold;
> +       return 0;
> +}
> +
> +static int page_owner_threshold_set(void *data, u64 val)
> +{
> +       page_owner_stack_threshold = val;

This could be written concurrently, so to avoid data races, you can
use WRITE_ONCE(page_owner_stack_threshold, val) and use
READ_ONCE(page_owner_stack_threshold) where it's read.

> +       return 0;
> +}
> +
> +DEFINE_SIMPLE_ATTRIBUTE(proc_page_owner_threshold, &page_owner_threshold_get,
> +                       &page_owner_threshold_set, "%llu");
> +
>  static int __init pageowner_init(void)
>  {
>         struct dentry *dir;
> @@ -898,6 +916,8 @@ static int __init pageowner_init(void)
>         dir = debugfs_create_dir("page_owner_stacks", NULL);
>         debugfs_create_file("show_stacks", 0400, dir, NULL,
>                             &page_owner_stack_operations);
> +       debugfs_create_file("set_threshold", 0600, dir, NULL,
> +                           &proc_page_owner_threshold);
>
>         return 0;
>  }
> --
> 2.43.0
>