linux-kernel - Re: [PATCH RFC] mm: Use pr_warn_once() for min_free

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Message-ID: <aK_7GKJ4BWjye4tZ@tiehlicka>
Date: Thu, 28 Aug 2025 08:45:44 +0200
From: Michal Hocko <mhocko@...e.com>
To: Weilin Tong <tongweilin@...ux.alibaba.com>
Cc: akpm@...ux-foundation.org, linux-mm@...ck.org, vbabka@...e.cz,
	surenb@...gle.com, jackmanb@...gle.com, hannes@...xchg.org,
	ziy@...dia.com, linux-kernel@...r.kernel.org,
	baolin.wang@...ux.alibaba.com
Subject: Re: [PATCH RFC] mm: Use pr_warn_once() for min_free_kbytes warning

On Thu 28-08-25 11:06:02, Weilin Tong wrote:
> When min_free_kbytes is user-configured, increasing system memory via memory
> hotplug may trigger multiple recalculations of min_free_kbytes. This results
> in excessive warning messages flooding the kernel log if several memory blocks
> are added in a short period.
> 
> Sample dmesg output before optimization:
> ...
> [ 1303.897214] min_free_kbytes is not updated to 126529 because user defined value 1048576 is preferred
> [ 1303.960498] min_free_kbytes is not updated to 126529 because user defined value 1048576 is preferred
> [ 1303.970116] min_free_kbytes is not updated to 126529 because user defined value 1048576 is preferred
> [ 1303.979709] min_free_kbytes is not updated to 126529 because user defined value 1048576 is preferred
> [ 1303.989254] min_free_kbytes is not updated to 126529 because user defined value 1048576 is preferred
> [ 1303.999122] min_free_kbytes is not updated to 126529 because user defined value 1048576 is preferred
> [ 1304.008644] min_free_kbytes is not updated to 126529 because user defined value 1048576 is preferred
> [ 1304.018537] min_free_kbytes is not updated to 126529 because user defined value 1048576 is preferred
> [ 1304.028054] min_free_kbytes is not updated to 126529 because user defined value 1048576 is preferred
> [ 1304.037615] min_free_kbytes is not updated to 126529 because user defined value 1048576 is preferred
> ...
> 
> Replace pr_warn() with pr_warn_once() to ensure only one warning is printed,
> preventing large volumes of repeated log entries and improving log readability.

pr_warn_once seems too aggressive as we could miss useful events. On the
other hand I agree that repeating the same message for each memory block
onlining is not really helpful. Would it make sense to only pr_warn when
new_min_free_kbytes differs from the previous one we have warned for?

> 
> Signed-off-by: Weilin Tong <tongweilin@...ux.alibaba.com>
> ---
>  mm/page_alloc.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index baead29b3e67..774723150e5b 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -6412,7 +6412,7 @@ void calculate_min_free_kbytes(void)
>  	if (new_min_free_kbytes > user_min_free_kbytes)
>  		min_free_kbytes = clamp(new_min_free_kbytes, 128, 262144);
>  	else
> -		pr_warn("min_free_kbytes is not updated to %d because user defined value %d is preferred\n",
> +		pr_warn_once("min_free_kbytes is not updated to %d because user defined value %d is preferred\n",
>  				new_min_free_kbytes, user_min_free_kbytes);
>  
>  }
> -- 
> 2.43.7

-- 
Michal Hocko
SUSE Labs