linux-kernel - Re: [PATCH resend] drop_caches: add some documentation and info message

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Message-Id: <20130731201708.efa5ae87.akpm@linux-foundation.org>
Date:	Wed, 31 Jul 2013 20:17:08 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
Cc:	mhocko@...e.cz, linux-mm@...ck.org, linux-kernel@...r.kernel.org,
	dave.hansen@...el.com, kamezawa.hiroyu@...fujitsu.com, bp@...e.de,
	dave@...ux.vnet.ibm.com
Subject: Re: [PATCH resend] drop_caches: add some documentation and info
 message

On Wed, 31 Jul 2013 23:11:50 -0400 KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com> wrote:

> >> --- a/fs/drop_caches.c
> >> +++ b/fs/drop_caches.c
> >> @@ -59,6 +59,8 @@ int drop_caches_sysctl_handler(ctl_table *table, int write,
> >>  	if (ret)
> >>  		return ret;
> >>  	if (write) {
> >> +		printk(KERN_INFO "%s (%d): dropped kernel caches: %d\n",
> >> +		       current->comm, task_pid_nr(current), sysctl_drop_caches);
> >>  		if (sysctl_drop_caches & 1)
> >>  			iterate_supers(drop_pagecache_sb, NULL);
> >>  		if (sysctl_drop_caches & 2)
> > 
> > How about we do
> > 
> > 	if (!(sysctl_drop_caches & 4))
> > 		printk(....)
> > 
> > so people can turn it off if it's causing problems?
> 
> The best interface depends on the purpose. If you want to detect crazy application,
> we can't assume an application co-operate us. So, I doubt this works.

You missed the "!".  I'm proposing that setting the new bit 2 will
permit people to prevent the new printk if it is causing them problems.
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