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

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Date:	Tue, 30 Jul 2013 14:55:25 +0200
From:	Michal Hocko <mhocko@...e.cz>
To:	Andrew Morton <akpm@...ux-foundation.org>
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 30-07-13 01:25:44, Andrew Morton wrote:
> 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?

What if we get crazy and need more of them?

> > So what about using 1<<31 instead?
> 
> Could, but negative (or is it positive?) numbers are a bit of a pain.

Yes, that was the point ;), I would like to make a new usage a dance on
the meadows.
But I do not care much, let's use 1<<30 if negative sounds too bad but I
would leave some room for further entities.

-- 
Michal Hocko
SUSE Labs
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