Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755671Ab2ECHYs (ORCPT ); Thu, 3 May 2012 03:24:48 -0400 Received: from mail-lpp01m010-f46.google.com ([209.85.215.46]:65422 "EHLO mail-lpp01m010-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752641Ab2ECHYr (ORCPT ); Thu, 3 May 2012 03:24:47 -0400 Date: Thu, 3 May 2012 10:24:42 +0300 (EEST) From: Pekka Enberg X-X-Sender: penberg@tux.localdomain To: Minchan Kim cc: linux-mm@kvack.org, LKML , Ingo Molnar , Anton Vorontsov , Leonid Moiseichuk Subject: Re: vmevent: question? In-Reply-To: <4F9E4F0A.8030900@kernel.org> Message-ID: References: <4F9E39F1.5030600@kernel.org> <4F9E44AD.8020701@kernel.org> <4F9E4F0A.8030900@kernel.org> User-Agent: Alpine 2.02 (LFD 1266 2009-07-14) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1302 Lines: 30 On Mon, 30 Apr 2012, Minchan Kim wrote: > > What kind of consistency guarantees do you mean? The data sent to > > userspace is always a snapshot of the state and therefore can be stale > > by the time it reaches userspace. > > Consistency between component of snapshot. > let's assume following as > > 1. User expect some events's value would be minus when event he expect happen. > A : -3, B : -4, C : -5, D : -6 > 2. Logically, it's not possible to mix plus and minus values for the events. > A : -3, B : -4, C : -5, D : -6 ( O ) > A : -3, B : -4, C : 1, D : 2 ( X ) > > But in current implementation, some of those could be minus and some of those could be plus. > Which event could user believe? > At least, we need a _captured_ value when event triggered so that user can ignore other values. Sorry, I still don't quite understand the problem. The current implementation provides the same kind of snapshot consistency as reading from /proc/vmstat does (modulo the fact that we read them twice) for the values we support. Pekka -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/