Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753638Ab3EPM14 (ORCPT ); Thu, 16 May 2013 08:27:56 -0400 Received: from seldrel01.sonyericsson.com ([212.209.106.2]:11159 "EHLO seldrel01.sonyericsson.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753441Ab3EPM1z (ORCPT ); Thu, 16 May 2013 08:27:55 -0400 From: Oskar Andero Date: Thu, 16 May 2013 14:27:52 +0200 To: Dave Chinner CC: "linux-kernel@vger.kernel.org" , "linux-mm@kvack.org" , "Lekanovic, Radovan" , David Rientjes , Glauber Costa , Andrew Morton , Hugh Dickins , Greg Kroah-Hartman Subject: Re: [PATCH] mm: vmscan: handle any negative return value from scan_objects Message-ID: <20130516122752.GG24072@caracas.corpusers.net> References: <1368693736-15486-1-git-send-email-oskar.andero@sonymobile.com> <20130516115212.GC11167@devil.localdomain> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Disposition: inline In-Reply-To: <20130516115212.GC11167@devil.localdomain> 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 Content-Length: 1710 Lines: 42 On 13:52 Thu 16 May , Dave Chinner wrote: > On Thu, May 16, 2013 at 10:42:16AM +0200, Oskar Andero wrote: > > The shrinkers must return -1 to indicate that it is busy. Instead, treat > > any negative value as busy. > > Why? The API defines return condition for aborting a scan and gives > a specific value for doing that. i.e. explain why should change the > API to over-specify the 'abort scan" return value like this. As I pointed out earlier, looking in to the code (from master): if (shrink_ret == -1) break; if (shrink_ret < nr_before) ret += nr_before - shrink_ret; This piece of code lacks a sanity check and will only function if shrink_ret is either greater than zero or exactly -1. If shrink_ret is e.g. -2 this will lead to undefined behaviour. > FWIW, using "any" negative number for "abort scan" is a bad API > design decision. It means that in future we can't introduce > different negative return values in the API if we have a new to. > i.e. each specific negative return value needs to have the potential > for defining a different behaviour. An alternative to my patch would be to add: if (shrink_ret < -1) /* handle illegal return code in some way */ > So if any change needs to be made, it is to change the -1 return > value to an enum and have the shrinkers return that enum when they > want an abort. I am all for an enum, but I still believe we should handle the case where the shrinkers return something wicked. -Oskar -- 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/