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

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

[Joel Granados]

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@kernel.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@kernel.org>

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

[Joel Granados]

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@kernel.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@kernel.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

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

[Christian Brauner]

On Thu, 13 Mar 2025 16:46:36 +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.
> 
> 
> [...]

Applied to the vfs-6.15.misc branch of the vfs/vfs.git tree.
Patches in the vfs-6.15.misc branch should appear in linux-next soon.

Please report any outstanding bugs that were missed during review in a
new review to the original patch series allowing us to drop it.

It's encouraged to provide Acked-bys and Reviewed-bys even though the
patch has now been applied. If possible patch trailers will be updated.

Note that commit hashes shown below are subject to change due to rebase,
trailer updates or similar. If in doubt, please check the listed branch.

tree:   https://git.kernel.org/pub/scm/linux/kernel/git/vfs/vfs.git
branch: vfs-6.15.misc

[1/1] drop_caches: Allow re-enabling message after disabling
      https://git.kernel.org/vfs/vfs/c/66c4cbae77e2

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

[Joel Granados]

On Fri, Mar 14, 2025 at 11:48:43AM +0100, Christian Brauner wrote:
> On Thu, 13 Mar 2025 16:46:36 +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.
> > 
> > 
> > [...]
> 
> Applied to the vfs-6.15.misc branch of the vfs/vfs.git tree.
> Patches in the vfs-6.15.misc branch should appear in linux-next soon.
> 
> Please report any outstanding bugs that were missed during review in a
> new review to the original patch series allowing us to drop it.
> 
> It's encouraged to provide Acked-bys and Reviewed-bys even though the
> patch has now been applied. If possible patch trailers will be updated.
> 
> Note that commit hashes shown below are subject to change due to rebase,
> trailer updates or similar. If in doubt, please check the listed branch.
> 
> tree:   https://git.kernel.org/pub/scm/linux/kernel/git/vfs/vfs.git
> branch: vfs-6.15.misc
> 
> [1/1] drop_caches: Allow re-enabling message after disabling
>       https://git.kernel.org/vfs/vfs/c/66c4cbae77e2

FYI, Sent out a V2 after discussion in [1]

[1]: https://lore.kernel.org/20250216100514.3948-1-rwchen404@gmail.com

-- 

Joel Granados