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=-8.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS 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 3F4CAC432BE for ; Tue, 31 Aug 2021 23:25:20 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id A126D60F91 for ; Tue, 31 Aug 2021 23:25:19 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.1 mail.kernel.org A126D60F91 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=shutemov.name Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=kvack.org Received: by kanga.kvack.org (Postfix) id 384D26B006C; Tue, 31 Aug 2021 19:25:19 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 30D2E8D0001; Tue, 31 Aug 2021 19:25:19 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 160CA6B0072; Tue, 31 Aug 2021 19:25:19 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0093.hostedemail.com [216.40.44.93]) by kanga.kvack.org (Postfix) with ESMTP id 03F436B006C for ; Tue, 31 Aug 2021 19:25:19 -0400 (EDT) Received: from smtpin01.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay05.hostedemail.com (Postfix) with ESMTP id 96F54180013E5 for ; Tue, 31 Aug 2021 23:25:18 +0000 (UTC) X-FDA: 78536959116.01.48471E5 Received: from mail-lj1-f171.google.com (mail-lj1-f171.google.com [209.85.208.171]) by imf18.hostedemail.com (Postfix) with ESMTP id 4F8474002085 for ; Tue, 31 Aug 2021 23:25:18 +0000 (UTC) Received: by mail-lj1-f171.google.com with SMTP id i28so1619305ljm.7 for ; Tue, 31 Aug 2021 16:25:18 -0700 (PDT) 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; bh=ReC2ox+Cju/4N9Fc/5sSAV7oCq75ICewzDo/R9c9AWY=; b=pN2iMhH1zDTCH5MDvXVSzuCCB8DDe5RwD/to1P+zYwgR3DO/7mbOMaR+UgXeGk6uEY VS+eBqv36wZzDcoK+gl28f4wVMGO0a8tRVlNE4KUWK5lS+DtIThtjNjrA5vFjnoLuFx5 SF2NE3vcEWAOMwE7kJMkKVnpiyuvH3aOqyjNU7QBSLTgSZ5pIhsY+ZobDcJz0MUqUiZi u9dKRXDo4CNeHOaWa022jYMGL/JGxNvl5/vr91LmlOC8nMa0dBivNRDi809sIPe+joPy TOkgWM6CTQr0rztXAn1t4byLi8pmM1TnYj+LEy+o7xklXItVtOLrir0qHRdiJhVga9uu TEDQ== 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; bh=ReC2ox+Cju/4N9Fc/5sSAV7oCq75ICewzDo/R9c9AWY=; b=mMYJMNuVkI8X8baoMvUwcnT5wwXpXCIQaMpV8dksQG7tOIX0XlXoJ1UjZNLLx+k8lU 9IXoLwvuLlZdJDhOlxweXaHAh5DcNsMgMJhW/fFLaMqHDpCLv0gwjliWDxyxU3SFnXmO E/oaEuVmbG62v6UVUvFIfBw+ObL8DIx9lua1nek8OLr0qvmy7fqgIPD4JfctiwRiOXJ4 L6HAlnq1/RwYMjB+mcF8mmGTm11p0+EIVP+cqhy8P1f9Bvf8EbYRge42CnWER7xYAgwH hQdrvPHUkkwY30kmPDxXn1LqEVpTt+fUqo48QT3TraqKXNjFi1cPijLO23kNNNJIS+oP 9dhA== X-Gm-Message-State: AOAM533YPc4QZP2c+m1Dudd2m8a4tJ8u4XBQjQjrYXbwi129achKpYo5 M6RtzmNchN+nN3PssNkERUdbEQ== X-Google-Smtp-Source: ABdhPJyzJabJ58N8ryzlDv9r2PjoUf90VHxMfkQhKyDBPDhi2KLOiYKJaoK8XeWY7SWSfyJ+pJ6UIQ== X-Received: by 2002:a2e:a4ba:: with SMTP id g26mr26698740ljm.254.1630452316794; Tue, 31 Aug 2021 16:25:16 -0700 (PDT) Received: from box.localdomain ([86.57.175.117]) by smtp.gmail.com with ESMTPSA id c3sm2344950ljj.77.2021.08.31.16.25.15 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 31 Aug 2021 16:25:16 -0700 (PDT) Received: by box.localdomain (Postfix, from userid 1000) id 44B20102EFE; Wed, 1 Sep 2021 02:25:16 +0300 (+03) Date: Wed, 1 Sep 2021 02:25:16 +0300 From: "Kirill A. Shutemov" To: Qi Zheng Cc: akpm@linux-foundation.org, tglx@linutronix.de, hannes@cmpxchg.org, mhocko@kernel.org, vdavydov.dev@gmail.com, kirill.shutemov@linux.intel.com, mika.penttila@nextfour.com, david@redhat.com, vbabka@suse.cz, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, songmuchun@bytedance.com Subject: Re: [PATCH v2 2/2] mm: remove redundant smp_wmb() Message-ID: <20210831232516.4ft2kkn63lngggbb@box.shutemov.name> References: <20210831132111.85437-1-zhengqi.arch@bytedance.com> <20210831132111.85437-3-zhengqi.arch@bytedance.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210831132111.85437-3-zhengqi.arch@bytedance.com> Authentication-Results: imf18.hostedemail.com; dkim=pass header.d=shutemov-name.20150623.gappssmtp.com header.s=20150623 header.b=pN2iMhH1; spf=none (imf18.hostedemail.com: domain of kirill@shutemov.name has no SPF policy when checking 209.85.208.171) smtp.mailfrom=kirill@shutemov.name; dmarc=none X-Stat-Signature: doyuuyeh4bedgxdnwg1p4o8h1bjftpe8 X-Rspamd-Queue-Id: 4F8474002085 X-Rspamd-Server: rspam04 X-HE-Tag: 1630452318-917558 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 Tue, Aug 31, 2021 at 09:21:11PM +0800, Qi Zheng wrote: > The smp_wmb() which is in the __pte_alloc() is used to > ensure all ptes setup is visible before the pte is made > visible to other CPUs by being put into page tables. We > only need this when the pte is actually populated, so > move it to pmd_install(). __pte_alloc_kernel(), > __p4d_alloc(), __pud_alloc() and __pmd_alloc() are similar > to this case. > > We can also defer smp_wmb() to the place where the pmd entry > is really populated by preallocated pte. There are two kinds > of user of preallocated pte, one is filemap & finish_fault(), > another is THP. The former does not need another smp_wmb() > because the smp_wmb() has been done by pmd_install(). > Fortunately, the latter also does not need another smp_wmb() > because there is already a smp_wmb() before populating the > new pte when the THP uses a preallocated pte to split a huge > pmd. > > Signed-off-by: Qi Zheng > Reviewed-by: Muchun Song > Acked-by: David Hildenbrand Acked-by: Kirill A. Shutemov -- Kirill A. Shutemov