linux-kernel - Re: [PATCH v2] drop_caches: re-enable message after disabling

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Message-ID: <zaiqpjvkekhgipcs7smqhbb7hqt5dcneyoyndycofjepitxznf@q22hsykugpme>
Date: Mon, 10 Mar 2025 14:51:11 +0100
From: Joel Granados <joel.granados@...nel.org>
To: Ruiwu Chen <rwchen404@...il.com>
Cc: mcgrof@...nel.org, corbet@....net, keescook@...omium.org, 
	linux-doc@...r.kernel.org, linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org, 
	viro@...iv.linux.org.uk, zachwade.k@...il.com
Subject: Re: [PATCH v2] drop_caches: re-enable message after disabling

On Sat, Mar 08, 2025 at 04:05:49PM +0800, Ruiwu Chen wrote:
> >> When 'echo 4 > /proc/sys/vm/drop_caches' the message is disabled,
> >> but there is no interface to enable the message, only by restarting
> >> the way, so add the 'echo 0 > /proc/sys/vm/drop_caches' way to
> >> enabled the message again.
> >> 
> >> Signed-off-by: Ruiwu Chen <rwchen404@...il.com>
> >
> > You are overcomplicating things, if you just want to re-enable messages
> > you can just use:
> >
> > -		stfu |= sysctl_drop_caches & 4;
> > +		stfu = sysctl_drop_caches & 4;
> >
> > The bool is there as 4 is intended as a bit flag, you can can figure
> > out what values you want and just append 4 to it to get the expected
> > result.
> >
> >  Luis
> 
> Is that what you mean ?
> 
> -               stfu |= sysctl_drop_caches & 4;
> +               stfu ^= sysctl_drop_caches & 4;
> 
> 'echo 4 > /sys/kernel/vm/drop_caches' can disable or open messages,
> This is what I originally thought, but there is uncertainty that when different operators execute the command,
> It is not possible to determine whether this time is enabled or turned on unless you operate it twice.

So can you use ^= or not? And what does operate it twice mean?

Best
> 
> Ruiwu
> 
> >
> >> ---
> >> v2: - updated Documentation/ to note this new API.
> >>     - renamed the variable.
...
> >> @@ -85,7 +88,7 @@ static const struct ctl_table drop_caches_table[] = {
> >>  		.maxlen		= sizeof(int),
> >>  		.mode		= 0200,
> >>  		.proc_handler	= drop_caches_sysctl_handler,
> >> -		.extra1		= SYSCTL_ONE,
> >> +		.extra1		= SYSCTL_ZERO,
> >>  		.extra2		= SYSCTL_FOUR,
> >>  	},
> >>  };
> >> -- 
> >> 2.27.0
> >> 

-- 

Joel Granados