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 17892C32767 for ; Fri, 3 Jan 2020 14:01:32 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id D931F222C4 for ; Fri, 3 Jan 2020 14:01:31 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org D931F222C4 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 6AD448E0005; Fri, 3 Jan 2020 09:01:31 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id 60F1D8E0003; Fri, 3 Jan 2020 09:01:31 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 4FE088E0005; Fri, 3 Jan 2020 09:01:31 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0138.hostedemail.com [216.40.44.138]) by kanga.kvack.org (Postfix) with ESMTP id 363F18E0003 for ; Fri, 3 Jan 2020 09:01:31 -0500 (EST) Received: from smtpin14.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay03.hostedemail.com (Postfix) with SMTP id DFCE88249980 for ; Fri, 3 Jan 2020 14:01:30 +0000 (UTC) X-FDA: 76336485540.14.show90_d2064d208b45 X-HE-Tag: show90_d2064d208b45 X-Filterd-Recvd-Size: 4063 Received: from mga01.intel.com (mga01.intel.com [192.55.52.88]) by imf12.hostedemail.com (Postfix) with ESMTP for ; Fri, 3 Jan 2020 14:01:29 +0000 (UTC) X-Amp-Result: UNKNOWN X-Amp-Original-Verdict: FILE UNKNOWN X-Amp-File-Uploaded: False Received: from fmsmga002.fm.intel.com ([10.253.24.26]) by fmsmga101.fm.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 03 Jan 2020 06:01:28 -0800 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.69,390,1571727600"; d="scan'208";a="252597773" Received: from richard.sh.intel.com (HELO localhost) ([10.239.159.54]) by fmsmga002.fm.intel.com with ESMTP; 03 Jan 2020 06:01:26 -0800 Date: Fri, 3 Jan 2020 22:01:28 +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: <20200103140128.GA26268@richard> Reply-To: Wei Yang References: <20191223222856.7189-1-richardw.yang@linux.intel.com> <20200103071846.GA16057@richard> <20200103130554.GA20078@richard> <20200103132650.jlyd37k6fcvycmy7@box> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200103132650.jlyd37k6fcvycmy7@box> User-Agent: Mutt/1.9.4 (2018-02-28) X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: 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? > >> >For the 2nd comment, the vma check. Let me take a further look to analysis. >> > >> >Thanks for Kirill's suggestion. >> > >> >> For 2nd comment, check vma could hold huge page. >> >> You mean do this check ? >> >> vma->vm_start <= address && vma->vm_end >= address + HPAGE_PMD_SIZE >> >> This happens after munmap a partial of the THP range? After doing so, we can >> skip split_pmd for this case. > >Okay, you are right. This kind of check would not be safe as we >split_huge_pmd_address() after adjusting VMA with expectation of splitting >PMD on boundary of the VMA. > >-- > Kirill A. Shutemov -- Wei Yang Help you, Help me