linux-kernel - Re: [RFC][PATCH] update /proc/sys/vm/drop

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Date:	Tue, 14 Sep 2010 23:14:22 -0700
From:	Dave Hansen <dave@...ux.vnet.ibm.com>
To:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
Cc:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	lnxninja@...ux.vnet.ibm.com
Subject: Re: [RFC][PATCH] update /proc/sys/vm/drop_caches documentation

On Wed, 2010-09-15 at 13:53 +0900, KOSAKI Motohiro wrote:
> > >  ==============================================================
> > >  
> > > diff -puN fs/drop_caches.c~update-drop_caches-documentation fs/drop_caches.c
> > > --- linux-2.6.git/fs/drop_caches.c~update-drop_caches-documentation	2010-09-14 15:44:29.000000000 -0700
> > > +++ linux-2.6.git-dave/fs/drop_caches.c	2010-09-14 15:58:31.000000000 -0700
> > > @@ -47,6 +47,8 @@ int drop_caches_sysctl_handler(ctl_table
> > >  {
> > >  	proc_dointvec_minmax(table, write, buffer, length, ppos);
> > >  	if (write) {
> > > +		WARN_ONCE(1, "kernel caches forcefully dropped, "
> > > +			     "see Documentation/sysctl/vm.txt\n");
> > 
> > Documentation updeta seems good but showing warning seems to be meddling to me.
> 
> Agreed.
> 
> If the motivation is blog's bogus rumor, this is no effective. I easily
> imazine they will write "Hey, drop_caches may output strange message, 
> but please ignore it!".

Fair enough.  But, is there a point that we _should_ be warning?  If
someone is doing this every minute, or every hour, something is pretty
broken.  Should we at least be doing a WARN_ON() so that the TAINT_WARN
is set?

I'm worried that there are users out there experiencing real problems
that aren't reporting it because "workarounds" like this just paper over
the issue.

-- Dave

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