From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wg0-f41.google.com (mail-wg0-f41.google.com [74.125.82.41]) by kanga.kvack.org (Postfix) with ESMTP id 08D556B0032 for ; Fri, 23 Jan 2015 00:14:55 -0500 (EST) Received: by mail-wg0-f41.google.com with SMTP id a1so5523152wgh.0 for ; Thu, 22 Jan 2015 21:14:54 -0800 (PST) Received: from mx1.redhat.com (mx1.redhat.com. [209.132.183.28]) by mx.google.com with ESMTPS id x6si366878wif.15.2015.01.22.21.14.52 for (version=TLSv1.2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Thu, 22 Jan 2015 21:14:53 -0800 (PST) Date: Fri, 23 Jan 2015 13:14:22 +0800 From: WANG Chao 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> Sender: owner-linux-mm@kvack.org List-ID: 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 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 -- 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