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=-10.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH, 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 F3AB0C4361B for ; Wed, 9 Dec 2020 17:58:34 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 6A0DA23C8F for ; Wed, 9 Dec 2020 17:58:34 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 6A0DA23C8F Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=linux-foundation.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id C366C8D002E; Wed, 9 Dec 2020 12:58:33 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id BC1326B00B4; Wed, 9 Dec 2020 12:58:33 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id AD4588D002E; Wed, 9 Dec 2020 12:58:33 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0007.hostedemail.com [216.40.44.7]) by kanga.kvack.org (Postfix) with ESMTP id 9491B6B00B2 for ; Wed, 9 Dec 2020 12:58:33 -0500 (EST) Received: from smtpin23.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay01.hostedemail.com (Postfix) with ESMTP id 499D6180AD80F for ; Wed, 9 Dec 2020 17:58:33 +0000 (UTC) X-FDA: 77574503706.23.dogs68_1e0c1a8273f1 Received: from filter.hostedemail.com (10.5.16.251.rfc1918.com [10.5.16.251]) by smtpin23.hostedemail.com (Postfix) with ESMTP id 1341237609 for ; Wed, 9 Dec 2020 17:58:33 +0000 (UTC) X-HE-Tag: dogs68_1e0c1a8273f1 X-Filterd-Recvd-Size: 4960 Received: from mail-lf1-f66.google.com (mail-lf1-f66.google.com [209.85.167.66]) by imf28.hostedemail.com (Postfix) with ESMTP for ; Wed, 9 Dec 2020 17:58:32 +0000 (UTC) Received: by mail-lf1-f66.google.com with SMTP id r24so4308725lfm.8 for ; Wed, 09 Dec 2020 09:58:32 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux-foundation.org; s=google; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=uJaVhTpiMPaliRW1BsTVPR0HUZ5LPD9/lyKWp6voxZY=; b=W3TAZiMxgQtdmGJSBJFklYY9V2kwPDqdPrz6VB+jV0dmuZj2xY806aorny+f833fr0 b8e17lxLA8lqeWSjVicsm8ZauNAfVbS1JSChtiKvqoRliqknYvhRrkhxg/15OsDnB8Ae F7O6VFdwmN7mFS6k9yL922iGj3GMtLKU5aDW0= X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=uJaVhTpiMPaliRW1BsTVPR0HUZ5LPD9/lyKWp6voxZY=; b=koj4Rcca5ryG/WKNjPZR8wkO4DEpT/Diax9GHtnQ1KJ8plteQ7w1QlO7f/uOkJuVNb LMlE8TRt3ZfIck04yqhyQhkJ2Bq6HhPJuGe8YRK0Ou2gCCU8Cb07eVm+bzpVD2GpqAzM arG1jd/NGNX/n4oQBVE3x3bBS1nCRIshek9TUP9WwIt76P6ylSm8IjPehpUnthfEXr/3 smxP/gdSwdAYwDWhrG3DdIRpP3QadHpfPXk7aBrZuYv30SGeOB+c6PtYbrrSGvd9tATG NZh6w5/r/OL2MHhW3sSVH3DsTUvFhxTH0hYyC2Qc9L5Q3TA5okSyZZb2pzW+l2pz24Hk b8SQ== X-Gm-Message-State: AOAM53200sCkx9WlACVPnLYuC3iT+uRQyigiyqkCubKk7CnFj9XlbUCv J+coIY3DOb8yJEqC466ZlU9tsTeVGktY9Q== X-Google-Smtp-Source: ABdhPJzbYxsJuGY29EjJ9FFhyy2VDtf7U/2F3yxpC9FPxqzCu07oDdHRbqDSPT0Fm3dwH1zMaZD+9Q== X-Received: by 2002:ac2:548b:: with SMTP id t11mr1357704lfk.181.1607536710309; Wed, 09 Dec 2020 09:58:30 -0800 (PST) Received: from mail-lj1-f171.google.com (mail-lj1-f171.google.com. [209.85.208.171]) by smtp.gmail.com with ESMTPSA id z20sm312338ljh.86.2020.12.09.09.58.29 for (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 09 Dec 2020 09:58:29 -0800 (PST) Received: by mail-lj1-f171.google.com with SMTP id x23so3441955lji.7 for ; Wed, 09 Dec 2020 09:58:29 -0800 (PST) X-Received: by 2002:a2e:5750:: with SMTP id r16mr1446782ljd.61.1607536708800; Wed, 09 Dec 2020 09:58:28 -0800 (PST) MIME-Version: 1.0 References: <20201209163950.8494-1-will@kernel.org> <20201209163950.8494-2-will@kernel.org> In-Reply-To: <20201209163950.8494-2-will@kernel.org> From: Linus Torvalds Date: Wed, 9 Dec 2020 09:58:12 -0800 X-Gmail-Original-Message-ID: Message-ID: Subject: Re: [PATCH 1/2] mm: Allow architectures to request 'old' entries when prefaulting To: Will Deacon Cc: Linux Kernel Mailing List , Linux-MM , Linux ARM , Catalin Marinas , Jan Kara , Minchan Kim , Andrew Morton , "Kirill A . Shutemov" , Vinayak Menon , Android Kernel Team Content-Type: text/plain; charset="UTF-8" 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 Wed, Dec 9, 2020 at 8:40 AM Will Deacon wrote: > > @@ -3978,8 +3994,17 @@ static vm_fault_t do_fault_around(struct vm_fault *vmf) > > /* check if the page fault is solved */ > vmf->pte -= (vmf->address >> PAGE_SHIFT) - (address >> PAGE_SHIFT); > - if (!pte_none(*vmf->pte)) > - ret = VM_FAULT_NOPAGE; > + if (pte_none(*vmf->pte)) > + goto out_unlock; > + > + if (vmf->flags & FAULT_FLAG_PREFAULT_OLD) { > + pte_t pte = pte_mkyoung(*vmf->pte); > + if (ptep_set_access_flags(vmf->vma, address, vmf->pte, pte, 0)) > + update_mmu_cache(vmf->vma, address, vmf->pte); > + } Oh, please dear God no. First you incorrectly set it old, and then you conditionally make it young again and as a result force an atomic rwm update and another TLB flush for no good reason. Just make sure that the FAULT_FLAG_PREFAULT_OLD never sets the *actual* address to old. And yes, that probably means that you need to change "alloc_set_pte()" to actually pass in the real address, and leave "vmf->address" alone - so that it can know which ones are prefaulted and which one is real, but that sounds like a good idea anyway. Then you can just make alloc_set_pte() do the right thing in the first place, instead of doing this nasty "lets do it wrong and fix it up later" horror. Linus