From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751752AbbAWFO7 (ORCPT ); Fri, 23 Jan 2015 00:14:59 -0500 Received: from mx1.redhat.com ([209.132.183.28]:45443 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750954AbbAWFO5 (ORCPT ); Fri, 23 Jan 2015 00:14:57 -0500 Date: Fri, 23 Jan 2015 13:14:22 +0800 From: WANG Chao To: Davidlohr Bueso Cc: Rik van Riel , Vlastimil Babka , 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 Message-ID: <20150123051422.GC8670@dhcp-129-179.nay.redhat.com> 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> <54C123CF.2070107@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <54C123CF.2070107@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 01/22/15 at 11:22am, Rik van Riel wrote: > 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 :) True. I didn't run any kind of benchmark, thus no numbers here. This is purely hypothetical. I'm glad to run some tests. For the sake of consistency, could you please show me a hint how do you measure at the first place? I can do hit-rate, but I don't know how you measure cpu cycles. Could you elaborate? Thanks WANG Chao