Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751991AbcCIFW6 (ORCPT ); Wed, 9 Mar 2016 00:22:58 -0500 Received: from www9186uo.sakura.ne.jp ([153.121.56.200]:60121 "EHLO www9186uo.sakura.ne.jp" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750932AbcCIFWh (ORCPT ); Wed, 9 Mar 2016 00:22:37 -0500 Date: Wed, 9 Mar 2016 14:22:35 +0900 From: Naoya Horiguchi To: Konstantin Khlebnikov Cc: Naoya Horiguchi , "linux-mm@kvack.org" , Andrew Morton , Vladimir Davydov , Linux Kernel Mailing List Subject: Re: [PATCH v1] tools/vm/page-types.c: remove memset() in walk_pfn() Message-ID: <20160309052235.GA28231@www9186uo.sakura.ne.jp> References: <1457401652-9226-1-git-send-email-n-horiguchi@ah.jp.nec.com> <20160308055834.GA9987@hori1.linux.bs1.fc.nec.co.jp> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-2022-jp Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.20 (2009-12-10) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3660 Lines: 103 On Wed, Mar 09, 2016 at 07:28:21AM +0300, Konstantin Khlebnikov wrote: > On Tue, Mar 8, 2016 at 8:58 AM, Naoya Horiguchi > wrote: > > 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? > > kpagecgroup_read() reads only if kpagecgroup were opened, > /proc/kpagecgroup might even not exist. Probably it's better to fill > them with zeros here. > Pre-memset was an optimization - it fills buffer only once instead on > each kpagecgroup_read() call. Ah, OK. So here's ver.2. Thanks, Naoya --- From: Naoya Horiguchi Subject: [PATCH v2] tools/vm/page-types.c: avoid memset() in walk_pfn() when count == 1 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 Most of time is spent in memset(). Currently memset() clears over whole buffer for every walk_pfn() call, which is inefficient when walk_pfn() is called from walk_vma(), because in that case walk_pfn() is called for each pfn. So this patch limits the zero initialization only for the first element. $ time ./page-types.patched -p $(pgrep -f test_alloc) ... real 0m0.182s user 0m0.046s sys 0m0.135s Fixes: 954e95584579 ("tools/vm/page-types.c: add memory cgroup dumping and filtering") Signed-off-by: Naoya Horiguchi Suggested-by: Konstantin Khlebnikov --- tools/vm/page-types.c | 10 +++++++++- 1 file changed, 9 insertions(+), 1 deletion(-) diff --git a/tools/vm/page-types.c b/tools/vm/page-types.c index dab61c377f54..e92903fc7113 100644 --- a/tools/vm/page-types.c +++ b/tools/vm/page-types.c @@ -633,7 +633,15 @@ static void walk_pfn(unsigned long voffset, unsigned long pages; unsigned long i; - memset(cgi, 0, sizeof cgi); + /* + * kpagecgroup_read() reads only if kpagecgroup were opened, but + * /proc/kpagecgroup might even not exist, so it's better to fill + * them with zeros here. + */ + if (count == 1) + cgi[0] = 0; + else + memset(cgi, 0, sizeof cgi); while (count) { batch = min_t(unsigned long, count, KPAGEFLAGS_BATCH); -- 2.4.3