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=-8.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, USER_AGENT_SANE_1 autolearn=unavailable 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 EF356C2D0CE for ; Fri, 3 Jan 2020 07:18:51 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id D1CDC2464B for ; Fri, 3 Jan 2020 07:18:51 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726427AbgACHSr (ORCPT ); Fri, 3 Jan 2020 02:18:47 -0500 Received: from mga01.intel.com ([192.55.52.88]:55587 "EHLO mga01.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725890AbgACHSq (ORCPT ); Fri, 3 Jan 2020 02:18:46 -0500 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; 02 Jan 2020 23:18:45 -0800 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.69,389,1571727600"; d="scan'208";a="252507763" Received: from richard.sh.intel.com (HELO localhost) ([10.239.159.54]) by fmsmga002.fm.intel.com with ESMTP; 02 Jan 2020 23:18:44 -0800 Date: Fri, 3 Jan 2020 15:18:46 +0800 From: Wei Yang To: Wei Yang Cc: 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: <20200103071846.GA16057@richard> Reply-To: Wei Yang References: <20191223222856.7189-1-richardw.yang@linux.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20191223222856.7189-1-richardw.yang@linux.intel.com> User-Agent: Mutt/1.9.4 (2018-02-28) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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(). For the 2nd comment, the vma check. Let me take a further look to analysis. Thanks for Kirill's suggestion. > >Signed-off-by: Wei Yang > >--- >v2: move the check into split_huge_pmd_address(). >--- > mm/huge_memory.c | 16 ++++++++++++++++ > 1 file changed, 16 insertions(+) > >diff --git a/mm/huge_memory.c b/mm/huge_memory.c >index 893fecd5daa4..2b9c2f412b32 100644 >--- a/mm/huge_memory.c >+++ b/mm/huge_memory.c >@@ -2342,6 +2342,22 @@ void split_huge_pmd_address(struct vm_area_struct *vma, unsigned long address, > pud_t *pud; > pmd_t *pmd; > >+ /* >+ * When page is not NULL, function is called by try_to_unmap_one() >+ * with TTU_SPLIT_HUGE_PMD set. There are two places set >+ * TTU_SPLIT_HUGE_PMD >+ * >+ * unmap_page() >+ * shrink_page_list() >+ * >+ * In both cases, the "page" here is the PageHead() of a THP. >+ * >+ * If the page is not a PMD mapped huge page, e.g. after mremap(), it >+ * is not necessary to split it. >+ */ >+ if (page && !IS_ALIGNED(address, HPAGE_PMD_SIZE)) >+ return; >+ > pgd = pgd_offset(vma->vm_mm, address); > if (!pgd_present(*pgd)) > return; >-- >2.17.1 -- Wei Yang Help you, Help me