From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx153.postini.com [74.125.245.153]) by kanga.kvack.org (Postfix) with SMTP id B15716B0002 for ; Wed, 15 May 2013 10:11:01 -0400 (EDT) From: Oskar Andero Date: Wed, 15 May 2013 16:10:57 +0200 Subject: Re: [RFC PATCH 0/2] return value from shrinkers Message-ID: <20130515141057.GA24072@caracas.corpusers.net> References: <1368454595-5121-1-git-send-email-oskar.andero@sonymobile.com> <5192523B.7030805@parallels.com> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Disposition: inline In-Reply-To: <5192523B.7030805@parallels.com> Sender: owner-linux-mm@kvack.org List-ID: To: Glauber Costa Cc: "linux-kernel@vger.kernel.org" , "linux-mm@kvack.org" , Hugh Dickins , Greg Kroah-Hartman , "Lekanovic, Radovan" , David Rientjes , Dave Chinner , Mel Gorman On 17:03 Tue 14 May , Glauber Costa wrote: > On 05/13/2013 06:16 PM, Oskar Andero wrote: > > Hi, > > > > In a previous discussion on lkml it was noted that the shrinkers use the > > magic value "-1" to signal that something went wrong. > > > > This patch-set implements the suggestion of instead using errno.h values > > to return something more meaningful. > > > > The first patch simply changes the check from -1 to any negative value and > > updates the comment accordingly. > > > > The second patch updates the shrinkers to return an errno.h value instead > > of -1. Since this one spans over many different areas I need input on what is > > a meaningful return value. Right now I used -EBUSY on everything for consitency. > > > > What do you say? Is this a good idea or does it make no sense at all? > > > > Thanks! > > > > Right now me and Dave are completely reworking the way shrinkers > operate. I suggest, first of all, that you take a look at that cautiously. Sounds good. Where can one find the code for that? > On the specifics of what you are doing here, what would be the benefit > of returning something other than -1 ? Is there anything we would do > differently for a return value lesser than 1? Firstly, what bugs me is the magic and unintuitiveness of using -1 rather than a more descriptive error code. IMO, even a #define SHRINK_ERROR -1 in some header file would be better. Expanding the test to <0 will open up for more granular error checks, like -EAGAIN, -EBUSY and so on. Currently, they would all be treated the same, but maybe in the future we would like to handle them differently? Finally, looking at the code: if (shrink_ret == -1) break; if (shrink_ret < nr_before) ret += nr_before - shrink_ret; This piece of code will only function if shrink_ret is either greater than zero or -1. If shrink_ret is -2 this will lead to undefined behaviour. > So far, shrink_slab behaves the same, you are just expanding the test. > If you really want to push this through, I would suggest coming up with > a more concrete reason for why this is wanted. I don't know how well this patch is aligned with your current rework, but based on my comments above, I don't see a reason for not taking it. -Oskar -- 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/ . Don't email: email@kvack.org