From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-qc0-f175.google.com (mail-qc0-f175.google.com [209.85.216.175]) by kanga.kvack.org (Postfix) with ESMTP id CBFAA6B0032 for ; Fri, 23 Jan 2015 20:02:38 -0500 (EST) Received: by mail-qc0-f175.google.com with SMTP id c9so427866qcz.6 for ; Fri, 23 Jan 2015 17:02:38 -0800 (PST) Received: from aserp1040.oracle.com (aserp1040.oracle.com. [141.146.126.69]) by mx.google.com with ESMTPS id j4si4225834qao.97.2015.01.23.17.02.37 for (version=TLSv1 cipher=RC4-SHA bits=128/128); Fri, 23 Jan 2015 17:02:38 -0800 (PST) Message-ID: <54C2EF09.3090407@oracle.com> Date: Fri, 23 Jan 2015 20:02:01 -0500 From: Sasha Levin MIME-Version: 1.0 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> <54C123CF.2070107@redhat.com> <20150123051422.GC8670@dhcp-129-179.nay.redhat.com> In-Reply-To: <20150123051422.GC8670@dhcp-129-179.nay.redhat.com> Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: WANG Chao , 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 01/23/2015 12:14 AM, WANG Chao wrote: > 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? I don't think there's a need to look for problems where there are none. Have you observed a performance issue that might be improved by changing the shift here? Thanks, Sasha -- 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