linux-kernel - Re: [PATCH] drop_caches: Allow re-enabling message after disabling

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Message-ID: <znixmeryizgqkb273xidczsgdh52tw3pv4ehfyoj6m2tcxycch@xal6ntp5f5mt>
Date: Thu, 13 Mar 2025 16:54:01 +0100
From: Joel Granados <joel.granados@...nel.org>
To: Jonathan Corbet <corbet@....net>, 
	Alexander Viro <viro@...iv.linux.org.uk>, Christian Brauner <brauner@...nel.org>, Jan Kara <jack@...e.cz>
Cc: linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org, 
	linux-fsdevel@...r.kernel.org, Ruiwu Chen <rwchen404@...il.com>, 
	Luis Chamberlain <mcgrof@...nel.org>
Subject: Re: [PATCH] drop_caches: Allow re-enabling message after disabling

On Thu, Mar 13, 2025 at 04:46:36PM +0100, Joel Granados wrote:
> After writing "4" to /proc/sys/vm/drop_caches there was no way to
> re-enable the drop_caches kernel message. By removing the "or" logic for
> the stfu variable in drop_cache_sysctl_handler, it is now possible to
> toggle the message on and off by setting the 4th bit in
> /proc/sys/vm/drop_caches.
> 
> Signed-off-by: Joel Granados <joel.granados@...nel.org>
> ---
>  Documentation/admin-guide/sysctl/vm.rst | 2 +-
>  fs/drop_caches.c                        | 2 +-
>  2 files changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/Documentation/admin-guide/sysctl/vm.rst b/Documentation/admin-guide/sysctl/vm.rst
> index f48eaa98d22d2b575f6e913f437b0d548daac3e6..75a032f8cbfb4e05f04610cca219d154bd852789 100644
> --- a/Documentation/admin-guide/sysctl/vm.rst
> +++ b/Documentation/admin-guide/sysctl/vm.rst
> @@ -266,7 +266,7 @@ used::
>  	cat (1234): drop_caches: 3
>  
>  These are informational only.  They do not mean that anything is wrong
> -with your system.  To disable them, echo 4 (bit 2) into drop_caches.
> +with your system.  To toggle them, echo 4 (bit 2) into drop_caches.
>  
>  enable_soft_offline
>  ===================
> diff --git a/fs/drop_caches.c b/fs/drop_caches.c
> index d45ef541d848a73cbd19205e0111c2cab3b73617..501b9f690445e245f88cbb31a5123b2752e2e7ce 100644
> --- a/fs/drop_caches.c
> +++ b/fs/drop_caches.c
> @@ -73,7 +73,7 @@ int drop_caches_sysctl_handler(const struct ctl_table *table, int write,
>  				current->comm, task_pid_nr(current),
>  				sysctl_drop_caches);
>  		}
> -		stfu |= sysctl_drop_caches & 4;
> +		stfu = sysctl_drop_caches & 4;
>  	}
>  	return 0;
>  }
> 
> ---
> base-commit: 7eb172143d5508b4da468ed59ee857c6e5e01da6
> change-id: 20250313-jag-drop_caches_msg-c4fbfedb51f3
> 
> Best regards,
> -- 
> Joel Granados <joel.granados@...nel.org>
> 
> 
In case you are curious:
This is a V3 of what was discussed in https://lore.kernel.org/20250216100514.3948-1-rwchen404@gmail.com
My bad for forgetting to tag it V3 :(.
Best


-- 

Joel Granados