From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754462Ab3F1Ae5 (ORCPT ); Thu, 27 Jun 2013 20:34:57 -0400 Received: from mail.linuxfoundation.org ([140.211.169.12]:39933 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753950Ab3F1Ae4 (ORCPT ); Thu, 27 Jun 2013 20:34:56 -0400 Date: Thu, 27 Jun 2013 17:34:33 -0700 From: Andrew Morton To: Minchan Kim Cc: Luiz Capitulino , linux-mm@kvack.org, linux-kernel@vger.kernel.org, mhocko@suse.cz, anton@enomsg.org, kmpark@infradead.org, hyunhee.kim@samsung.com Subject: Re: [PATCH v2] vmpressure: implement strict mode Message-Id: <20130627173433.d0fc6ecd.akpm@linux-foundation.org> In-Reply-To: <20130628000201.GB15637@bbox> References: <20130626231712.4a7392a7@redhat.com> <20130627150231.2bc00e3efcd426c4beef894c@linux-foundation.org> <20130628000201.GB15637@bbox> X-Mailer: Sylpheed 2.7.1 (GTK+ 2.18.9; x86_64-redhat-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, 28 Jun 2013 09:02:01 +0900 Minchan Kim wrote: > Hi Andrew, > > On Thu, Jun 27, 2013 at 03:02:31PM -0700, Andrew Morton wrote: > > On Wed, 26 Jun 2013 23:17:12 -0400 Luiz Capitulino wrote: > > > > > Currently, an eventfd is notified for the level it's registered for > > > _plus_ higher levels. > > > > > > This is a problem if an application wants to implement different > > > actions for different levels. For example, an application might want > > > to release 10% of its cache on level low, 50% on medium and 100% on > > > critical. To do this, an application has to register a different > > > eventfd for each pressure level. However, fd low is always going to > > > be notified and and all fds are going to be notified on level critical. > > > > > > Strict mode solves this problem by strictly notifiying an eventfd > > > for the pressure level it registered for. This new mode is optional, > > > by default we still notify eventfds on higher levels too. > > > > > > > It didn't take long for this simple interface to start getting ugly :( > > And having the fd operate in different modes is ugly. > > > > Can we instead pass the level in the event payload? > > You mean userland have to look the result of read(2) to confirm what > current level is and if it's no interest for us, we don't do any reaction. Something like that. It's flexible, simple, keeps policy in userspace. > If so, userland daemon would receive lots of events which are no interest. "lots"? If vmpressure is generating events at such a high frequency that this matters then it's already busted?