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

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Message-ID: <CAHGf_=r7mek+ueJWfu_6giMOueDTnMs8dY1jJrKyX+gfPys6uA@mail.gmail.com>
Date:	Thu, 1 Aug 2013 21:39:48 -0400
From:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Michal Hocko <mhocko@...e.cz>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	LKML <linux-kernel@...r.kernel.org>, dave.hansen@...el.com,
	KAMEZAWA Hiroyuki <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 Wed, Jul 31, 2013 at 11:17 PM, Andrew Morton
<akpm@...ux-foundation.org> wrote:
> 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.

No I don't. I'm sure almost all abuse users think our usage is correct. Then,
I can imagine all crazy applications start to use this flag eventually.
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