From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S262372AbTJFRjn (ORCPT ); Mon, 6 Oct 2003 13:39:43 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S262395AbTJFRjm (ORCPT ); Mon, 6 Oct 2003 13:39:42 -0400 Received: from mail.kroah.org ([65.200.24.183]:37067 "EHLO perch.kroah.org") by vger.kernel.org with ESMTP id S262372AbTJFRjg (ORCPT ); Mon, 6 Oct 2003 13:39:36 -0400 Date: Mon, 6 Oct 2003 10:38:58 -0700 From: Greg KH To: Dipankar Sarma Cc: Maneesh Soni , Al Viro , Patrick Mochel , LKML Subject: Re: [RFC 0/6] Backing Store for sysfs Message-ID: <20031006173858.GA4403@kroah.com> References: <20031006085915.GE4220@in.ibm.com> <20031006160846.GA4125@us.ibm.com> <20031006173111.GA1788@in.ibm.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20031006173111.GA1788@in.ibm.com> User-Agent: Mutt/1.4.1i Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Oct 06, 2003 at 11:01:11PM +0530, Dipankar Sarma wrote: > On Mon, Oct 06, 2003 at 09:08:46AM -0700, Greg KH wrote: > > On Mon, Oct 06, 2003 at 02:29:15PM +0530, Maneesh Soni wrote: > > > > > > 2.6.0-test6 With patches. > > > ----------------- > > > dentry_cache (active) 2520 2544 > > > inode_cache (active) 1058 1050 > > > LowFree 875032 KB 874748 KB > > > > So with these patches we actually eat up more LowFree if all sysfs > > entries are searched, and make the dentry_cache bigger? That's not good :( > > My guess is that those 24 dentries are just noise. What we should > do is verify with a large number of devices if the numbers are all > that different after a walk of the sysfs tree. Ok, a better test would be with a _lot_ of devices. Care to test with a lot of scsi debug devices? > > Remember, every kobject that's created will cause a call to > > /sbin/hotplug which will cause udev to walk the sysfs tree to get the > > information for that kobject. So I don't see any savings in these > > patches, do you? > > Assuming that unused files/dirs are aged out of dentry and inode cache, > it should benefit. The numbers you should look at are - > > -------------------------------------------------------- > After mounting sysfs > ------------------- > dentry_cache (active) 2350 1321 > inode_cache (active) 1058 31 > LowFree 875096 KB 875836 KB > -------------------------------------------------------- > > That saves ~800KB. If you just mount sysfs and use a few files, you > aren't eating up dentries and inodes for every file in sysfs. How often > do you expect hotplug events to happen in a system ? Every kobject that is created and is associated with a subsystem generates a hotplug call. So that's about every kobject that we care about here :) > Some time after a hotplug event, dentries/inodes will get aged out and > then you should see savings. It should greatly benefit in a normal > system. Can you show this happening? > Now if the additional kobjects cause problems with userland hotplug, then > that needs to be resolved. However that seems to be a different problem > altogether. Could you please elaborate on that ? No, I don't think the additional ones you have added will cause problems, but can you verify this? Just log all hotplug events happening in your system (point /proc/sys/kernel/hotplug to a simple logging program). But again, I don't think the added overhead you have added to a kobject is acceptable for not much gain for the normal case (systems without a zillion devices.) thanks, greg k-h