From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx141.postini.com [74.125.245.141]) by kanga.kvack.org (Postfix) with SMTP id CFCED6B0032 for ; Fri, 2 Aug 2013 12:04:08 -0400 (EDT) Received: by mail-oa0-f45.google.com with SMTP id m1so1715837oag.32 for ; Fri, 02 Aug 2013 09:04:08 -0700 (PDT) Date: Fri, 02 Aug 2013 11:04:02 -0500 From: Rob Landley Subject: Re: [PATCH resend] drop_caches: add some documentation and info message In-Reply-To: <20130731201708.efa5ae87.akpm@linux-foundation.org> (from akpm@linux-foundation.org on Wed Jul 31 22:17:08 2013) Message-Id: <1375459442.8422.1@driftwood> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii; DelSp=Yes; Format=Flowed Content-Disposition: inline Content-Transfer-Encoding: quoted-printable Sender: owner-linux-mm@kvack.org List-ID: To: Andrew Morton Cc: KOSAKI Motohiro , mhocko@suse.cz, linux-mm@kvack.org, linux-kernel@vger.kernel.org, dave.hansen@intel.com, kamezawa.hiroyu@jp.fujitsu.com, bp@suse.de, dave@linux.vnet.ibm.com On 07/31/2013 10:17:08 PM, Andrew Morton wrote: > On Wed, 31 Jul 2013 23:11:50 -0400 KOSAKI Motohiro =20 > wrote: >=20 > > >> --- a/fs/drop_caches.c > > >> +++ b/fs/drop_caches.c > > >> @@ -59,6 +59,8 @@ int drop_caches_sysctl_handler(ctl_table =20 > *table, int write, > > >> if (ret) > > >> return ret; > > >> if (write) { > > >> + printk(KERN_INFO "%s (%d): dropped kernel =20 > caches: %d\n", > > >> + current->comm, task_pid_nr(current), =20 > 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 =20 > crazy application, > > we can't assume an application co-operate us. So, I doubt this =20 > works. >=20 > 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 =20 > problems. Or an alternative for those planning to patch it down to a KERN_DEBUG =20 locally. I'd be surprised if anybody who does this sees the printk and thinks =20 "hey, I'll dig into the VM's balancing logic and come up to speed on =20 the tradeoffs sufficient to contribute to kernel development" because =20 of something in dmesg. Anybody actually annoyed by it will chop out the =20 printk (you barely need to know C to do that), the rest won't notice. Rob= -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org