From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-vc0-f180.google.com (mail-vc0-f180.google.com [209.85.220.180]) by kanga.kvack.org (Postfix) with ESMTP id C16726B0032 for ; Thu, 22 Jan 2015 11:23:11 -0500 (EST) Received: by mail-vc0-f180.google.com with SMTP id hy10so589754vcb.11 for ; Thu, 22 Jan 2015 08:23:11 -0800 (PST) Received: from mx1.redhat.com (mx1.redhat.com. [209.132.183.28]) by mx.google.com with ESMTPS id vw3si9362758vcb.30.2015.01.22.08.23.09 for (version=TLSv1.2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Thu, 22 Jan 2015 08:23:10 -0800 (PST) Message-ID: <54C123CF.2070107@redhat.com> Date: Thu, 22 Jan 2015 11:22:39 -0500 From: Rik van Riel 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> In-Reply-To: <1421943573.4903.24.camel@stgolabs.net> Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: 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 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 :) -- 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