From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S938751Ab0KBGbI (ORCPT ); Tue, 2 Nov 2010 02:31:08 -0400 Received: from smtp.nokia.com ([147.243.1.47]:37685 "EHLO mgw-sa01.nokia.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755573Ab0KBGa6 (ORCPT ); Tue, 2 Nov 2010 02:30:58 -0400 Subject: Re: [RFC PATCH] device-core: sysfs open - close notify From: Onkalo Samu Reply-To: samu.p.onkalo@nokia.com To: ext Alan Cox Cc: Ming Lei , "gregkh@suse.de" , "hmh@hmh.eng.br" , "akpm@linux-foundation.org" , "linux-kernel@vger.kernel.org" In-Reply-To: <20101101171126.1194e2b0@linux.intel.com> References: <1288529170-28890-1-git-send-email-samu.p.onkalo@nokia.com> <20101101171126.1194e2b0@linux.intel.com> Content-Type: text/plain; charset="UTF-8" Organization: Nokia Oyj Date: Tue, 02 Nov 2010 08:30:08 +0200 Message-ID: <1288679408.2080.18.camel@noppispoppis.nmp.nokia.com> Mime-Version: 1.0 X-Mailer: Evolution 2.28.3 Content-Transfer-Encoding: 7bit X-Nokia-AV: Clean Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, 2010-11-01 at 18:11 +0100, ext Alan Cox wrote: > > Your patch may cause many unnecessary memory waste because > > most of drivers does not need attribute file .open/.close notifier. > > Firstly there are not that many driver objects in a small system so it > wouldn't take that much to shift the balance the other way. Secondly > its becoming clear that every time a driver goes to runtime pm these > issues come up - even with things like configuration values for drivers > that need to wake the hardware and then silence it. > > So the whole sysfs/open thing is going to keep haunting us with runtime > pm, the question is where to put the callbacks so we don't bloat stuff. > Clearly not per attribute or per sysfs node. One possibility would be > with the runtime pm stuff, but that would need a clean reliable way to > go sysfs->device->runtime_pm > > There are also obvious hackish ways to handle it like passing a 0 > length read to indicate close etc - they save memory but they are > asking for problems in future. > Memory footprint could be minimized by combining separate open close functions to one like sysfs_open_close_notify and the actual operation would be a call parameter. But is that hackish? And perhaps some flags could be used to indicate which attributes trigs the open / close notification. -Samu