From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-2.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 820ACC33C9B for ; Wed, 8 Jan 2020 00:36:58 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 50DCB207E0 for ; Wed, 8 Jan 2020 00:36:58 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 50DCB207E0 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=linux.intel.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id EA3EA8E0005; Tue, 7 Jan 2020 19:36:57 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id E7B4C8E0001; Tue, 7 Jan 2020 19:36:57 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id DB8648E0005; Tue, 7 Jan 2020 19:36:57 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0128.hostedemail.com [216.40.44.128]) by kanga.kvack.org (Postfix) with ESMTP id C743E8E0001 for ; Tue, 7 Jan 2020 19:36:57 -0500 (EST) Received: from smtpin09.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay03.hostedemail.com (Postfix) with SMTP id 640648249980 for ; Wed, 8 Jan 2020 00:36:57 +0000 (UTC) X-FDA: 76352602074.09.wash21_76e3d50ea130e X-HE-Tag: wash21_76e3d50ea130e X-Filterd-Recvd-Size: 3962 Received: from mga03.intel.com (mga03.intel.com [134.134.136.65]) by imf38.hostedemail.com (Postfix) with ESMTP for ; Wed, 8 Jan 2020 00:36:56 +0000 (UTC) X-Amp-Result: UNKNOWN X-Amp-Original-Verdict: FILE UNKNOWN X-Amp-File-Uploaded: False Received: from orsmga008.jf.intel.com ([10.7.209.65]) by orsmga103.jf.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 07 Jan 2020 16:36:54 -0800 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.69,407,1571727600"; d="scan'208";a="215785978" Received: from richard.sh.intel.com (HELO localhost) ([10.239.159.54]) by orsmga008.jf.intel.com with ESMTP; 07 Jan 2020 16:36:53 -0800 Date: Wed, 8 Jan 2020 08:36:56 +0800 From: Wei Yang To: "Kirill A. Shutemov" Cc: Wei Yang , akpm@linux-foundation.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, kirill.shutemov@linux.intel.com, willy@infradead.org Subject: Re: [Patch v2] mm/rmap.c: split huge pmd when it really is Message-ID: <20200108003656.GB13943@richard> Reply-To: Wei Yang References: <20191223222856.7189-1-richardw.yang@linux.intel.com> <20200103071846.GA16057@richard> <20200103130554.GA20078@richard> <20200103132650.jlyd37k6fcvycmy7@box> <20200103140128.GA26268@richard> <20200107120333.ncvds3atyfiilxi3@box> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200107120333.ncvds3atyfiilxi3@box> User-Agent: Mutt/1.9.4 (2018-02-28) X-Bogosity: Ham, tests=bogofilter, spamicity=0.000013, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Tue, Jan 07, 2020 at 03:03:33PM +0300, Kirill A. Shutemov wrote: >On Fri, Jan 03, 2020 at 10:01:28PM +0800, Wei Yang wrote: >> On Fri, Jan 03, 2020 at 04:26:50PM +0300, Kirill A. Shutemov wrote: >> >On Fri, Jan 03, 2020 at 09:05:54PM +0800, Wei Yang wrote: >> >> On Fri, Jan 03, 2020 at 03:18:46PM +0800, Wei Yang wrote: >> >> >On Tue, Dec 24, 2019 at 06:28:56AM +0800, Wei Yang wrote: >> >> >>When page is not NULL, function is called by try_to_unmap_one() with >> >> >>TTU_SPLIT_HUGE_PMD set. There are two cases to call try_to_unmap_one() >> >> >>with TTU_SPLIT_HUGE_PMD set: >> >> >> >> >> >> * unmap_page() >> >> >> * shrink_page_list() >> >> >> >> >> >>In both case, the page passed to try_to_unmap_one() is PageHead() of the >> >> >>THP. If this page's mapping address in process is not HPAGE_PMD_SIZE >> >> >>aligned, this means the THP is not mapped as PMD THP in this process. >> >> >>This could happen when we do mremap() a PMD size range to an un-aligned >> >> >>address. >> >> >> >> >> >>Currently, this case is handled by following check in __split_huge_pmd() >> >> >>luckily. >> >> >> >> >> >> page != pmd_page(*pmd) >> >> >> >> >> >>This patch checks the address to skip some work. >> >> > >> >> >I am sorry to forget address Kirill's comment in 1st version. >> >> > >> >> >The first one is the performance difference after this change for a PTE >> >> >mappged THP. >> >> > >> >> >Here is the result:(in cycle) >> >> > >> >> > Before Patched >> >> > >> >> > 963 195 >> >> > 988 40 >> >> > 895 78 >> >> > >> >> >Average 948 104 >> >> > >> >> >So the change reduced 90% time for function split_huge_pmd_address(). >> > >> >Right. >> > >> >But do we have a scenario, where the performance of >> >split_huge_pmd_address() matters? I mean, it it called as part of rmap >> >walk, attempt to split huge PMD where we don't have huge PMD should be >> >within noise. >> >> Sorry for my poor English. >> >> I don't catch the meaning of the last sentence. "within noise" here means >> non-huge PMD is an expected scenario and we could tolerate this? > >Basically, I doubt that this change would bring any measurable perfromance >benefits on a real workload. > Ok, let's leave it now. >-- > Kirill A. Shutemov -- Wei Yang Help you, Help me