From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1750985AbXDNIuz (ORCPT ); Sat, 14 Apr 2007 04:50:55 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1750808AbXDNIuz (ORCPT ); Sat, 14 Apr 2007 04:50:55 -0400 Received: from e35.co.us.ibm.com ([32.97.110.153]:45864 "EHLO e35.co.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752548AbXDNIux (ORCPT ); Sat, 14 Apr 2007 04:50:53 -0400 Date: Sat, 14 Apr 2007 13:43:08 +0530 From: Maneesh Soni To: Matt Mackall Cc: Nick Piggin , Andrew Morton , William Lee Irwin III , linux-kernel@vger.kernel.org Subject: Re: [PATCH 0/13] maps: pagemap, kpagemap, and related cleanups Message-ID: <20070414081308.GA20034@in.ibm.com> Reply-To: maneesh@in.ibm.com References: <20070412231050.GN2986@holomorphy.com> <20070412163235.dd030637.akpm@linux-foundation.org> <461ECB9C.8060000@yahoo.com.au> <20070412174201.065068b2.akpm@linux-foundation.org> <461ED96C.5030606@yahoo.com.au> <20070412182213.a18cc4a7.akpm@linux-foundation.org> <461EE005.6070605@yahoo.com.au> <20070413015712.GL11115@waste.org> <461EE925.1000301@yahoo.com.au> <20070413022345.GN11115@waste.org> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20070413022345.GN11115@waste.org> User-Agent: Mutt/1.5.11 Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Apr 12, 2007 at 09:23:45PM -0500, Matt Mackall wrote: > On Fri, Apr 13, 2007 at 12:21:25PM +1000, Nick Piggin wrote: > > Matt Mackall wrote: > > >On Fri, Apr 13, 2007 at 11:42:29AM +1000, Nick Piggin wrote: > > > > >>If kprobes is simply crappy and doesn't work properly for this, then I > > >>could accept that. I'm not someone trying to get this info. So why can't > > >>it be used? (not just for kpagemap, but for clear_refs and all that gunk > > >>too). > > > > > > > > >kprobes is good for looking at events, but bad for looking at state. > > >Especially metric shitloads of state. > > > > Why? Why is a kprobes trap significantly more expensive than a read > > syscall? > > I guess I'm not clear on what you're proposing. From my understanding > of kprobes (admittedly not an expert), this is hard to do and not a > very good match. > > > >>Maybe. How about LRU? Reclaim performance is bad, and you want to work out > > >>which pages keep going off the end of it, or which pages keep getting > > >>written out via it, or who's pages are on the active list, forcing mine > > >>out. > > > > > > > > >Those are actually probably a good match for systemtap as they're all > > >events. > > > > Traverse the LRU? Which files do they belong to? What process maps them? > > -ENOPARSE. > For non-event based data gathering using kprobes we can have a debugfs file like /debug/kprobes/snapshot_probe and write a kprobe module with probe at ->write() function and then the user space can trigger the data collection echo "1" > /debug/kprobes/snapshot_probe Thus, the actual data collection code can reside in a separate module or a systemtap script which provides very good post-processing capabalities, and can be used without recompiling or rebooting the kernel. Thanks Maneesh -- Maneesh Soni Linux Technology Center, IBM India Systems and Technology Lab, Bangalore, India