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=DKIM_SIGNED,DKIM_VALID, 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 4BBE5C33C8C for ; Tue, 7 Jan 2020 12:03:40 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 1D0A724679 for ; Tue, 7 Jan 2020 12:03:39 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=shutemov-name.20150623.gappssmtp.com header.i=@shutemov-name.20150623.gappssmtp.com header.b="n+0QxgTR" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728052AbgAGMDj (ORCPT ); Tue, 7 Jan 2020 07:03:39 -0500 Received: from mail-lf1-f68.google.com ([209.85.167.68]:43885 "EHLO mail-lf1-f68.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726690AbgAGMDi (ORCPT ); Tue, 7 Jan 2020 07:03:38 -0500 Received: by mail-lf1-f68.google.com with SMTP id 9so38686913lfq.10 for ; Tue, 07 Jan 2020 04:03:37 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=shutemov-name.20150623.gappssmtp.com; s=20150623; h=date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to:user-agent; bh=gkoRQx7irojuK+AWr/fLDGMtpmCItYQJTiOcOz48ACA=; b=n+0QxgTRTK+O2mf2FrXFPMjkxXK9rEctLCKl7/Qmdza+cwZhJP09nDM8rSsQvEbBbJ l9xAT2cPkb+XZ0T0MifRSWx6pRTHnotF/Y9gp6eYSjbB/B7EXbzm9EBD/hq0H4nO60lC +KJMLmBHQQAZ/RgGzCcwDgOJRtXNo/60Tea7sAaUgmmLAQzOdA3OPj264qTC3azIlMzK KtkeHjSvBDRs765nessxAHlEJ5mILJMIDdoVr8pP2O6PWEzWgBkO79FETFM1KYAoPRWM u9lb5vWXaaBx68VTSOXu0w08x06BeeIVvnCnwtlMgRqOeja8rVsBL/miBa1IAMQNhtRf W8gg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to:user-agent; bh=gkoRQx7irojuK+AWr/fLDGMtpmCItYQJTiOcOz48ACA=; b=e/WNsb+JnLql8WyriN/2bLPGSvLHZl1kF+G+ScWUFIYtE/dRPtBXD6iRpryDom9IqO WpGu3S9wK97PZD+5T24blbpWKV2XJLbLS7WEu0e7oVIhrSob9fjxGZ9R4dYAUs7dmPz3 zJxg6KaZo35iHSVlXOrqhmsAx1Z1e3/M0VqsIlFwb80BN/kt+Yds7AtVSZAPafTR1EBt C/pHADccGbZ1VTMCEVzOHIpzRGYNDJRTT28H4FbA3H43lSI9RVZrsfzAENp3RKq74nAm GCyXDwKwF1uBWxiAVYv+IsP151jQjPvkaEcIHN2Uh588Flx3Xa5iaZEHqzwu+UePc4T+ 2CQw== X-Gm-Message-State: APjAAAXwJkDCs4U9VBRAYi65inFEQ1odeGlFeQqSkBVV25vX9fPWOT3g fCeuWkLSHQgweFSj3ymP5KcqL9EQf6U= X-Google-Smtp-Source: APXvYqzTBgc3YByXYy02WwN48Cp1z5N43Low+Z32HRlP66qeJ6xWFSJ5GppAsWUMBTFCnMxxTNpkFg== X-Received: by 2002:ac2:44ce:: with SMTP id d14mr60046304lfm.140.1578398616746; Tue, 07 Jan 2020 04:03:36 -0800 (PST) Received: from box.localdomain ([86.57.175.117]) by smtp.gmail.com with ESMTPSA id i19sm30413526lfj.17.2020.01.07.04.03.35 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 07 Jan 2020 04:03:35 -0800 (PST) Received: by box.localdomain (Postfix, from userid 1000) id 5F9341009CA; Tue, 7 Jan 2020 15:03:33 +0300 (+03) Date: Tue, 7 Jan 2020 15:03:33 +0300 From: "Kirill A. Shutemov" 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: <20200107120333.ncvds3atyfiilxi3@box> References: <20191223222856.7189-1-richardw.yang@linux.intel.com> <20200103071846.GA16057@richard> <20200103130554.GA20078@richard> <20200103132650.jlyd37k6fcvycmy7@box> <20200103140128.GA26268@richard> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200103140128.GA26268@richard> User-Agent: NeoMutt/20180716 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 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. -- Kirill A. Shutemov