From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail143.messagelabs.com (mail143.messagelabs.com [216.82.254.35]) by kanga.kvack.org (Postfix) with ESMTP id 368F76B003D for ; Tue, 28 Apr 2009 13:43:01 -0400 (EDT) Subject: Re: [PATCH 5/5] proc: export more page flags in /proc/kpageflags From: Matt Mackall In-Reply-To: <20090428093621.GD21085@elte.hu> References: <20090428010907.912554629@intel.com> <20090428014920.769723618@intel.com> <20090428065507.GA2024@elte.hu> <20090428074031.GK27382@one.firstfloor.org> <1240909484.1982.16.camel@penberg-laptop> <20090428091508.GA21085@elte.hu> <84144f020904280219p197d5ceag846ae9a80a76884e@mail.gmail.com> <84144f020904280225h490ef682p8973cb1241a1f3ea@mail.gmail.com> <20090428093621.GD21085@elte.hu> Content-Type: text/plain Date: Tue, 28 Apr 2009 12:42:08 -0500 Message-Id: <1240940528.938.426.camel@calx> Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org To: Ingo Molnar Cc: Pekka Enberg , Andi Kleen , Wu Fengguang , Steven Rostedt , =?ISO-8859-1?Q?Fr=E9d=E9ric?= Weisbecker , Larry Woodman , Peter Zijlstra , Eduard - Gabriel Munteanu , Andrew Morton , LKML , KOSAKI Motohiro , Alexey Dobriyan , "linux-mm@kvack.org" List-ID: On Tue, 2009-04-28 at 11:36 +0200, Ingo Molnar wrote: > I 'integrate' traces all the time to get summary counts. This series > of dynamic events: > > allocation > page count up > page count up > page count down > page count up > page count up > page count up > page count up > > integrates into: "page count is 6". Perhaps you've failed calculus. The integral is 6 + C. This is a critical distinction. Tracing is great for looking at changes, but it completely falls down for static system-wide measurements because it would require integrating from time=0 to get a meaningful summation. That's completely useless for taking a measurement on a system that already has an uptime of months. Never mind that summing up page flag changes for every page on the system since boot time through the trace interface is incredibly wasteful given that we're keeping a per-page integral in the page tables anyway. Tracing is not the answer for everything. -- http://selenic.com : development and support for Mercurial and Linux -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org