From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757780AbbA3Btn (ORCPT ); Thu, 29 Jan 2015 20:49:43 -0500 Received: from szxga01-in.huawei.com ([119.145.14.64]:26259 "EHLO szxga01-in.huawei.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752058AbbA3Btm (ORCPT ); Thu, 29 Jan 2015 20:49:42 -0500 Message-ID: <54CAE316.1070300@huawei.com> Date: Fri, 30 Jan 2015 09:49:10 +0800 From: xiakaixu User-Agent: Mozilla/5.0 (Windows NT 6.1; rv:17.0) Gecko/20130801 Thunderbird/17.0.8 MIME-Version: 1.0 To: Kaixu Xia , , , , , Namhyung Kim CC: , Subject: Re: [PATCH] perf: remove the extra validity check on nr_pages References: <1422352512-75150-1-git-send-email-xiakaixu@huawei.com> In-Reply-To: <1422352512-75150-1-git-send-email-xiakaixu@huawei.com> Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 8bit X-Originating-IP: [10.111.101.23] X-CFilter-Loop: Reflected Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 于 2015/1/27 17:55, Kaixu Xia 写道: ping... > The function is_power_of_2() also do the check on nr_pages, > so the first check performed is unnecessary. On the other > hand, the key point is to ensure @nr_pages is a power-of-two > number and mostly @nr_pages is a nonzero value, so in the > most cases, the function is_power_of_2() will be called. > > Signed-off-by: Kaixu Xia > --- > kernel/events/core.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/kernel/events/core.c b/kernel/events/core.c > index 882f835..abb57c2 100644 > --- a/kernel/events/core.c > +++ b/kernel/events/core.c > @@ -4268,7 +4268,7 @@ static int perf_mmap(struct file *file, struct vm_area_struct *vma) > * If we have rb pages ensure they're a power-of-two number, so we > * can do bitmasks instead of modulo. > */ > - if (nr_pages != 0 && !is_power_of_2(nr_pages)) > + if (!is_power_of_2(nr_pages)) > return -EINVAL; > > if (vma_size != PAGE_SIZE * (1 + nr_pages)) >