From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752624Ab3F1Spw (ORCPT ); Fri, 28 Jun 2013 14:45:52 -0400 Received: from mail-pa0-f52.google.com ([209.85.220.52]:53528 "EHLO mail-pa0-f52.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751084Ab3F1Spu (ORCPT ); Fri, 28 Jun 2013 14:45:50 -0400 Date: Fri, 28 Jun 2013 11:45:47 -0700 From: Anton Vorontsov To: Luiz Capitulino Cc: Andrew Morton , Minchan Kim , linux-mm@kvack.org, linux-kernel@vger.kernel.org, mhocko@suse.cz, kmpark@infradead.org, hyunhee.kim@samsung.com Subject: Re: [PATCH v2] vmpressure: implement strict mode Message-ID: <20130628184547.GA14287@teo> References: <20130628000201.GB15637@bbox> <20130627173433.d0fc6ecd.akpm@linux-foundation.org> <20130628005852.GA8093@teo> <20130627181353.3d552e64.akpm@linux-foundation.org> <20130628043411.GA9100@teo> <20130628050712.GA10097@teo> <20130628100027.31504abe@redhat.com> <20130628165722.GA12271@teo> <20130628170917.GA12610@teo> <20130628142558.5da3d030@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20130628142558.5da3d030@redhat.com> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Jun 28, 2013 at 02:25:58PM -0400, Luiz Capitulino wrote: > > > > That's how it's expected to work, because on strict mode you're notified > > > > for the level you registered for. So apps registering for critical, will > > > > still be notified on critical just like before. > > > > > > Suppose you introduce a new level, and the system hits this level. Before, > > > the app would receive at least some notification for the given memory load > > > (i.e. one of the old levels), with the new level introduced in the kernel, > > > the app will receive no events at all. > > That's not true. If an app registered for critical it will still get > critical notification when the system is at the critical level. Just as it > always did. No new events will change this. > > With today's semantics though, new events will change when current events > are triggered. So each new extension will cause applications to have > different behaviors, in different kernel versions. This looks quite > undesirable to me. I'll try to explain it again. Old behaviour: low -> event x <- but the system is at this unnamed level, between low and med med crit We add a level: low low-med <- system at this state, we send an event, but the old app does not know about it, so it won't receive *any* notifications. (In older kernels it would receive low level notification med crit You really don't see a problem here? I see the problem, and I see these solutions: 1. Use current scheme. 2. Add versioning. 3. Never change the levels (how can we know?) Anton