Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932505AbcCHF7z (ORCPT ); Tue, 8 Mar 2016 00:59:55 -0500 Received: from TYO201.gate.nec.co.jp ([210.143.35.51]:35658 "EHLO tyo201.gate.nec.co.jp" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932350AbcCHF7X convert rfc822-to-8bit (ORCPT ); Tue, 8 Mar 2016 00:59:23 -0500 From: Naoya Horiguchi To: Konstantin Khlebnikov CC: "linux-mm@kvack.org" , Andrew Morton , Vladimir Davydov , "Linux Kernel Mailing List" , Naoya Horiguchi Subject: Re: [PATCH v1] tools/vm/page-types.c: remove memset() in walk_pfn() Thread-Topic: [PATCH v1] tools/vm/page-types.c: remove memset() in walk_pfn() Thread-Index: AQHReNx/9SZwXk+xzUihMhHwIwfUip9OaYiAgAAM+AA= Date: Tue, 8 Mar 2016 05:58:35 +0000 Message-ID: <20160308055834.GA9987@hori1.linux.bs1.fc.nec.co.jp> References: <1457401652-9226-1-git-send-email-n-horiguchi@ah.jp.nec.com> In-Reply-To: Accept-Language: ja-JP, en-US Content-Language: ja-JP X-MS-Has-Attach: X-MS-TNEF-Correlator: x-originating-ip: [10.128.101.25] Content-Type: text/plain; charset="iso-2022-jp" Content-ID: <29A89ACCD05C694FA194AD1C0D1652EE@gisp.nec.co.jp> Content-Transfer-Encoding: 8BIT MIME-Version: 1.0 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1809 Lines: 52 On Tue, Mar 08, 2016 at 08:12:09AM +0300, Konstantin Khlebnikov wrote: > On Tue, Mar 8, 2016 at 4:47 AM, Naoya Horiguchi > wrote: > > I found that page-types is very slow and my testing shows many timeout errors. > > Here's an example with a simple program allocating 1000 thps. > > > > $ time ./page-types -p $(pgrep -f test_alloc) > > ... > > real 0m17.201s > > user 0m16.889s > > sys 0m0.312s > > > > $ time ./page-types.patched -p $(pgrep -f test_alloc) > > ... > > real 0m0.182s > > user 0m0.046s > > sys 0m0.135s > > > > Most of time is spent in memset(), which isn't necessary because we check > > that the return of kpagecgroup_read() is equal to pages and uninitialized > > memory is never used. So we can drop this memset(). > > These zeros are used in show_page_range() - for merging pages into ranges. Hi Konstantin, Thank you for the response. The below code does solve the problem, so that's fine. But I don't understand how the zeros are used. show_page_range() is called via add_page() which is called for i=0 to i=pages-1, and the buffer cgi is already filled for the range [i, pages-1] by kpagecgroup_read(), so even if without zero initialization, kpagecgroup_read() properly fills zeros, right? IOW, is there any problem if we don't do this zero initialization? Thanks, Naoya Horiguchi > You could add fast-path for count=1 > > @@ -633,7 +633,10 @@ static void walk_pfn(unsigned long voffset, > unsigned long pages; > unsigned long i; > > - memset(cgi, 0, sizeof cgi); > + if (count == 1) > + cgi[0] = 0; > + else > + memset(cgi, 0, sizeof cgi); > > while (count) { > batch = min_t(unsigned long, count, KPAGEFLAGS_BATCH); >