From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754006AbbAVQXQ (ORCPT ); Thu, 22 Jan 2015 11:23:16 -0500 Received: from mx1.redhat.com ([209.132.183.28]:54046 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752676AbbAVQXO (ORCPT ); Thu, 22 Jan 2015 11:23:14 -0500 Message-ID: <54C123CF.2070107@redhat.com> Date: Thu, 22 Jan 2015 11:22:39 -0500 From: Rik van Riel User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.3.0 MIME-Version: 1.0 To: Davidlohr Bueso , WANG Chao CC: Andrew Morton , Ingo Molnar , Peter Zijlstra , Michel Lespinasse , Mel Gorman , linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] mm, vmacache: Add kconfig VMACACHE_SHIFT References: <1421908189-18938-1-git-send-email-chaowang@redhat.com> <1421912761.4903.22.camel@stgolabs.net> <20150122075742.GA11335@dhcp-129-179.nay.redhat.com> <1421943573.4903.24.camel@stgolabs.net> In-Reply-To: <1421943573.4903.24.camel@stgolabs.net> Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 01/22/2015 11:19 AM, Davidlohr Bueso wrote: > On Thu, 2015-01-22 at 15:57 +0800, WANG Chao wrote: >> Hi, Davidlohr >> >> On 01/21/15 at 11:46pm, Davidlohr Bueso wrote: >>> On Thu, 2015-01-22 at 14:29 +0800, WANG Chao wrote: >>>> Add a new kconfig option VMACACHE_SHIFT (as a power of 2) to specify the >>>> number of slots vma cache has for each thread. Range is chosen 0-4 (1-16 >>>> slots) to consider both overhead and performance penalty. Default is 2 >>>> (4 slots) as it originally is, which provides good enough balance. >>>> >>> >>> Nack. I don't feel comfortable making scalability features of core code >>> configurable. >> >> Out of respect, is this a general rule not making scalability features >> of core code configurable? > > I doubt its a rule, just common sense. Users have no business > configuring such low level details. The optimizations need to > transparently work for everyone. There may sometimes be a good reason for making this kind of thing configurable, but since there were no performance numbers in the changelog, I have not seen any such reason for this particular change :)