From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx162.postini.com [74.125.245.162]) by kanga.kvack.org (Postfix) with SMTP id 434046B0044 for ; Mon, 30 Apr 2012 04:36:29 -0400 (EDT) Message-ID: <4F9E4F0A.8030900@kernel.org> Date: Mon, 30 Apr 2012 17:36:26 +0900 From: Minchan Kim MIME-Version: 1.0 Subject: Re: vmevent: question? References: <4F9E39F1.5030600@kernel.org> <4F9E44AD.8020701@kernel.org> In-Reply-To: Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Pekka Enberg Cc: linux-mm@kvack.org, LKML , Ingo Molnar , Anton Vorontsov , Leonid Moiseichuk On 04/30/2012 05:01 PM, Pekka Enberg wrote: > Hi Minchan, > > On Mon, Apr 30, 2012 at 10:52 AM, Minchan Kim wrote: >>> It makes the userspace side simpler for "lowmem notification" use >>> case. I'm open to changing the ABI if it doesn't make the userspace >>> side too complex. >> >> Yes. I understand your point but if we still consider all of values, >> we don't have any way to capture exact values except triggered event value. >> I mean there is no lock to keep consistency. >> If stale data is okay, no problem but IMHO, it could make user very confusing. >> So let's return value for first matched event if various event match. >> Of course, let's write down it in ABI. >> If there is other idea for reporting all of item with consistent, I'm okay. > > 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. > > If your code needs stricter consistency guarantees, you probably want > to do it in the kernel. > > Pekka > > -- > 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/ . > Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ > Don't email: email@kvack.org > -- Kind regards, Minchan Kim -- 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/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: email@kvack.org