Re: [PATCH 1/2] mm: replace custom bad page map ratelimiting logic

["Lorenzo Stoakes (ARM)" <ljs@kernel.org>]

On Tue, Aug 11, 2026 at 06:21:55PM +0100, Pedro Falcato wrote:
> The current logic (allow up to $BURST prints per minute) can be entirely
> replaced by the generic version in lib/ratelimit.c, used around the kernel.
>
> Do so. The only functional difference should be that the new logs will
> read something like:
>
> KERN_WARNING "print_bad_page_map: %d callbacks suppressed\n", ...
>
> But that should be fine enough.
>
> Signed-off-by: Pedro Falcato <pfalcato@suse.de>

Oh I love this :) seems __ratelimited() uses a try-lock on a spinlock internally
but I don't think that's an issue, a spurious not-rate-limted output on any
contention isn't really a big problem.

So LGTM and:

Reviewed-by: Lorenzo Stoakes (ARM) <ljs@kernel.org>

> ---
>  mm/memory.c | 30 +++---------------------------
>  1 file changed, 3 insertions(+), 27 deletions(-)
>
> diff --git a/mm/memory.c b/mm/memory.c
> index 4134ac607ee0..b4be57b590ce 100644
> --- a/mm/memory.c
> +++ b/mm/memory.c
> @@ -492,32 +492,8 @@ static inline void add_mm_rss_vec(struct mm_struct *mm, int *rss)
>  			add_mm_counter(mm, i, rss[i]);
>  }
>
> -static bool is_bad_page_map_ratelimited(void)
> -{
> -	static unsigned long resume;
> -	static unsigned long nr_shown;
> -	static unsigned long nr_unshown;
> -
> -	/*
> -	 * Allow a burst of 60 reports, then keep quiet for that minute;
> -	 * or allow a steady drip of one report per second.
> -	 */
> -	if (nr_shown == 60) {
> -		if (time_before(jiffies, resume)) {
> -			nr_unshown++;
> -			return true;
> -		}
> -		if (nr_unshown) {
> -			pr_alert("BUG: Bad page map: %lu messages suppressed\n",
> -				 nr_unshown);
> -			nr_unshown = 0;
> -		}
> -		nr_shown = 0;
> -	}
> -	if (nr_shown++ == 0)
> -		resume = jiffies + 60 * HZ;
> -	return false;
> -}
> +/* Allow a burst of 60 bad page map reports per minute. */
> +static DEFINE_RATELIMIT_STATE(bad_page_map_ratelimit, 60 * HZ, 60);
>
>  static void ptval_bytes_to_hex_str(char *buf, size_t buf_size, const void *entry, size_t entry_size)
>  {
> @@ -633,7 +609,7 @@ static void print_bad_page_map(struct vm_area_struct *vma,
>  	char entry_str[PTVAL_STR_MAX];
>  	pgoff_t index, anon_index;
>
> -	if (is_bad_page_map_ratelimited())
> +	if (!__ratelimit(&bad_page_map_ratelimit))
>  		return;
>
>  	mapping = vma->vm_file ? vma->vm_file->f_mapping : NULL;
> --
> 2.55.0
>

--
Cheers, Lorenzo