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=ham 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 D1236C2D0C2 for ; Fri, 3 Jan 2020 13:05:57 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id AE6D8206DB for ; Fri, 3 Jan 2020 13:05:57 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727736AbgACNF5 (ORCPT ); Fri, 3 Jan 2020 08:05:57 -0500 Received: from mga18.intel.com ([134.134.136.126]:23936 "EHLO mga18.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727350AbgACNF4 (ORCPT ); Fri, 3 Jan 2020 08:05:56 -0500 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 orsmga106.jf.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 03 Jan 2020 05:05:54 -0800 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.69,390,1571727600"; d="scan'208";a="214460872" Received: from richard.sh.intel.com (HELO localhost) ([10.239.159.54]) by orsmga008.jf.intel.com with ESMTP; 03 Jan 2020 05:05:52 -0800 Date: Fri, 3 Jan 2020 21:05:54 +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: <20200103130554.GA20078@richard> Reply-To: Wei Yang References: <20191223222856.7189-1-richardw.yang@linux.intel.com> <20200103071846.GA16057@richard> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200103071846.GA16057@richard> 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 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(). > >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. >> >>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 -- Wei Yang Help you, Help me