From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S965618Ab2KAU07 (ORCPT ); Thu, 1 Nov 2012 16:26:59 -0400 Received: from atrey.karlin.mff.cuni.cz ([195.113.26.193]:50650 "EHLO atrey.karlin.mff.cuni.cz" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S964942Ab2KAU05 (ORCPT ); Thu, 1 Nov 2012 16:26:57 -0400 Date: Thu, 1 Nov 2012 21:26:54 +0100 From: Pavel Machek To: Andrew Morton Cc: Dave Hansen , Michal Hocko , linux-mm@kvack.org, KAMEZAWA Hiroyuki , KOSAKI Motohiro , LKML Subject: Re: [PATCH] add some drop_caches documentation and info messsge Message-ID: <20121101202503.GA20817@xo-6d-61-c0.localdomain> References: <20121012125708.GJ10110@dhcp22.suse.cz> <20121023164546.747e90f6.akpm@linux-foundation.org> <20121024062938.GA6119@dhcp22.suse.cz> <20121024125439.c17a510e.akpm@linux-foundation.org> <50884F63.8030606@linux.vnet.ibm.com> <20121024134836.a28d223a.akpm@linux-foundation.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20121024134836.a28d223a.akpm@linux-foundation.org> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi! > > > hmpf. This patch worries me. If there are people out there who are > > > regularly using drop_caches because the VM sucks, it seems pretty > > > obnoxious of us to go dumping stuff into their syslog. What are they > > > supposed to do? Stop using drop_caches? > > > > People use drop_caches because they _think_ the VM sucks, or they > > _think_ they're "tuning" their system. _They_ are supposed to stop > > using drop_caches. :) > > Well who knows. Could be that people's vm *does* suck. Or they have > some particularly peculiar worklosd or requirement[*]. Or their VM > *used* to suck, and the drop_caches is not really needed any more but > it's there in vendor-provided code and they can't practically prevent > it. Or they have ipw wifi that does order 5 allocation :-). I seen drop_caches used in some android code, as part of SD card handling IIRC. > > What kind of interface _is_ it in the first place? Is it really a > > production-level thing that we expect users to be poking at? Or, is it > > a rarely-used debugging and benchmarking knob which is fair game for us > > to tweak like this? > > It was a rarely-used mainly-developer-only thing which, apparently, real > people found useful at some point in the past. Perhaps we should never > have offered it. And yes, documentation would be good. IIRC you claimed that drop_caches is not safe to use year-or-so-ago, is that still true? Pavel -- (english) http://www.livejournal.com/~pavelmachek (cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html