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

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Message-Id: <20130730012544.2f33ebf6.akpm@linux-foundation.org>
Date:	Tue, 30 Jul 2013 01:25:44 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Michal Hocko <mhocko@...e.cz>
Cc:	linux-mm@...ck.org, linux-kernel@...r.kernel.org,
	dave.hansen@...el.com, kosaki.motohiro@...fujitsu.com,
	kamezawa.hiroyu@...fujitsu.com, bp@...e.de,
	Dave Hansen <dave@...ux.vnet.ibm.com>
Subject: Re: [PATCH resend] drop_caches: add some documentation and info
 message

On Tue, 30 Jul 2013 09:45:31 +0200 Michal Hocko <mhocko@...e.cz> wrote:

> On Mon 29-07-13 13:57:43, Andrew Morton wrote:
> > On Fri, 26 Jul 2013 14:44:29 +0200 Michal Hocko <mhocko@...e.cz> 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?
> 
> I am OK with that  but can we use a top bit instead. Maybe we never have
> other entities to drop in the future but it would be better to have a room for them
> just in case.

If we add another flag in the future it can use bit 3?

> So what about using 1<<31 instead?

Could, but negative (or is it positive?) numbers are a bit of a pain.
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