From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753075AbXDMCgu (ORCPT ); Thu, 12 Apr 2007 22:36:50 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1753086AbXDMCgu (ORCPT ); Thu, 12 Apr 2007 22:36:50 -0400 Received: from waste.org ([66.93.16.53]:32980 "EHLO waste.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753045AbXDMCgt (ORCPT ); Thu, 12 Apr 2007 22:36:49 -0400 Date: Thu, 12 Apr 2007 21:23:45 -0500 From: Matt Mackall To: Nick Piggin Cc: Andrew Morton , William Lee Irwin III , linux-kernel@vger.kernel.org Subject: Re: [PATCH 0/13] maps: pagemap, kpagemap, and related cleanups Message-ID: <20070413022345.GN11115@waste.org> References: <1.486631555@selenic.com> <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> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <461EE925.1000301@yahoo.com.au> User-Agent: Mutt/1.5.13 (2006-08-11) Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org 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. -- Mathematics is the supreme nostalgia of our time.