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=-6.0 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS 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 DDE20C48BDF for ; Thu, 10 Jun 2021 23:04:26 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id C3DBA613F5 for ; Thu, 10 Jun 2021 23:04:26 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231147AbhFJXGW (ORCPT ); Thu, 10 Jun 2021 19:06:22 -0400 Received: from us-smtp-delivery-124.mimecast.com ([170.10.133.124]:60870 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230368AbhFJXGU (ORCPT ); Thu, 10 Jun 2021 19:06:20 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1623366263; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=Kn4921Fy2QxClPboKoVBlarBT42fXZONHXvZsMc4G14=; b=APFp1kQLqm/VxcHMem0c8P4f5Z0Xe0pUOUCRGoIWHkFswrmqOFh++H5j53G/+tmc7rBJFY Ayjr4Trg3/tMsFCMLg9ibGgGYkjLInb+RfGvuk7BEJNSiFxx5XULYPz8ljh9dntgnnx9jT fQYwjI1WDBM4mXl+/2vbBZZTFB030b8= Received: from mail-qt1-f199.google.com (mail-qt1-f199.google.com [209.85.160.199]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-412-1yQC9o8YNNmjJimyUzPI_g-1; Thu, 10 Jun 2021 19:04:22 -0400 X-MC-Unique: 1yQC9o8YNNmjJimyUzPI_g-1 Received: by mail-qt1-f199.google.com with SMTP id z20-20020ac845540000b0290248cbf50215so828100qtn.10 for ; Thu, 10 Jun 2021 16:04:22 -0700 (PDT) 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=Kn4921Fy2QxClPboKoVBlarBT42fXZONHXvZsMc4G14=; b=tYGSHShJRV/wQAqbAaoJdqzeb3aQHiA4z3dOtDgis/5aLQdcTHCWc69atcYZsG0Hab 23/b5FiQfHqS4OuYpASV+5RkEY0sDbQ1CoiIPmneyIfChZn1GxneRnEfgq6rdpk4G1DM rJdKoaJIEcbNBX9JEzVrW4fZCY56V7SstjTaZ4qMY/V48aXzMKjlxAi7oQ79Y7L3fP1i As4RHCd6uveS9QLGAscqQzmYPmaNKKOfhGvq4adpmsQv2xD9pZEYEiQdNRAKE0JbT8GZ /B8C41M0bZOKDmLLHtPa28mfqKZa/utr7Y1Qf38nEEtIMDrBf2imyfdo/pONWkdzg2FX /ktQ== X-Gm-Message-State: AOAM530lxqif3GbV/uSEiPIO7ZOKDSkvy8U42yXW+vVYaxQBzNL4/UFv kAzoh9BSTOyPj/MzwS+/FDaCkyeuhVjSwdXDTlqKGTba7hoYZzmd0TtsotTF3ZXb/I1KQ7Gg23P ZEyRv6COwHJADgN+FQoz9TCE3 X-Received: by 2002:a05:620a:1116:: with SMTP id o22mr1055474qkk.263.1623366261642; Thu, 10 Jun 2021 16:04:21 -0700 (PDT) X-Google-Smtp-Source: ABdhPJwrG/yfGVS5sWgTKcNo1dgRgBZLWinZ0GsXIy0VHGuGgZrohA7iNbV+b0qys3C0GTOZDsvbFg== X-Received: by 2002:a05:620a:1116:: with SMTP id o22mr1055448qkk.263.1623366261403; Thu, 10 Jun 2021 16:04:21 -0700 (PDT) Received: from t490s (bras-base-toroon474qw-grc-88-174-93-75-200.dsl.bell.ca. [174.93.75.200]) by smtp.gmail.com with ESMTPSA id j14sm3076434qtj.96.2021.06.10.16.04.19 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 10 Jun 2021 16:04:20 -0700 (PDT) Date: Thu, 10 Jun 2021 19:04:19 -0400 From: Peter Xu To: Alistair Popple Cc: linux-mm@kvack.org, akpm@linux-foundation.org, rcampbell@nvidia.com, linux-doc@vger.kernel.org, nouveau@lists.freedesktop.org, hughd@google.com, linux-kernel@vger.kernel.org, dri-devel@lists.freedesktop.org, hch@infradead.org, bskeggs@redhat.com, jgg@nvidia.com, shakeelb@google.com, jhubbard@nvidia.com, willy@infradead.org, Christoph Hellwig Subject: Re: [PATCH v10 07/10] mm: Device exclusive memory access Message-ID: References: <20210607075855.5084-1-apopple@nvidia.com> <2773835.D95cIkl9rl@nvdebian> <6429491.QiJgnDeYu7@nvdebian> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <6429491.QiJgnDeYu7@nvdebian> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Jun 11, 2021 at 12:21:26AM +1000, Alistair Popple wrote: > > Hmm, the thing is.. to me FOLL_SPLIT_PMD should have similar effect to explicit > > call split_huge_pmd_address(), afaict. Since both of them use __split_huge_pmd() > > internally which will generate that unwanted CLEAR notify. > > Agree that gup calls __split_huge_pmd() via split_huge_pmd_address() > which will always CLEAR. However gup only calls split_huge_pmd_address() if it > finds a thp pmd. In follow_pmd_mask() we have: > > if (likely(!pmd_trans_huge(pmdval))) > return follow_page_pte(vma, address, pmd, flags, &ctx->pgmap); > > So I don't think we have a problem here. Sorry I didn't follow here.. We do FOLL_SPLIT_PMD after this check, right? I mean, if it's a thp for the current mm, afaict pmd_trans_huge() should return true above, so we'll skip follow_page_pte(); then we'll check FOLL_SPLIT_PMD and do the split, then the CLEAR notify. Hmm.. Did I miss something? -- Peter Xu 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=-3.6 required=3.0 tests=BAYES_00,DKIM_INVALID, DKIM_SIGNED,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS 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 20FB0C49EAF for ; Sun, 27 Jun 2021 03:35:30 +0000 (UTC) Received: from gabe.freedesktop.org (gabe.freedesktop.org [131.252.210.177]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id E514A619B6 for ; Sun, 27 Jun 2021 03:35:29 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org E514A619B6 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=nouveau-bounces@lists.freedesktop.org Received: from gabe.freedesktop.org (localhost [127.0.0.1]) by gabe.freedesktop.org (Postfix) with ESMTP id 586296E141; Sun, 27 Jun 2021 03:34:47 +0000 (UTC) Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [216.205.24.124]) by gabe.freedesktop.org (Postfix) with ESMTPS id 36D3C6EE12 for ; Thu, 10 Jun 2021 23:04:29 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1623366268; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=Kn4921Fy2QxClPboKoVBlarBT42fXZONHXvZsMc4G14=; b=OspLjVdBrTS0a31bZ/j7D4WtHZ3kkzTZ3ogiNMWyOcex8w00P94RpQ7B0fNDNT5WxWmuGa 8nGtngbAfzXDG/K1Ky5BZ5r2xGS0PfbfZ+oDeJpbbo/Dp8+jKkW7jygmJOIlrsH/JT7cx3 bUQnmUFp4PV4dvDMDqCY4WhHRSvUFNY= Received: from mail-qt1-f200.google.com (mail-qt1-f200.google.com [209.85.160.200]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-233-KqYHAhRwPxCSGlAuvHBzpw-1; Thu, 10 Jun 2021 19:04:22 -0400 X-MC-Unique: KqYHAhRwPxCSGlAuvHBzpw-1 Received: by mail-qt1-f200.google.com with SMTP id b20-20020ac87fd40000b02901e1370c5e12so808460qtk.17 for ; Thu, 10 Jun 2021 16:04:22 -0700 (PDT) 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=Kn4921Fy2QxClPboKoVBlarBT42fXZONHXvZsMc4G14=; b=sLPYxvACo6AyNKxy8DOReJjcS21usZ0dPnjPv0bqzvp8KP2X5EXf1gwVoOy3NAZPwl xtrAun9FEz8gPgV3np/iFUdadO0ou2UxDw8EqJ4tH4awiIm9Co88andssU1auYRwNipV f3svSqO/1cbvpUcrkleTu5EzeTL84//T+bJySoUWK7lkiTdALCbtmd+sWoUx9I/sBUc4 HrL7a7dh6N7vOHcos0MuLQKlgptb2shvyggW4xxN057hNhtnyBYXvZw0PAevSG4GQxb5 PAX5IGnPdwJYcvEZWU4HIw2wDlkM69l7KW5bdxcmVy86cs2TdqtAjPxYBJ/Us19XuS5D uONQ== X-Gm-Message-State: AOAM531LAx9KijQ99nZG+QR0nJc3VhkhCk3o06vcoKUjlzZtzgz/oyp7 28u4hbCoP+HU+7zQfgp05CksWxsT8zmwvDe6wO3fCZbfwk+1BdLY2StnEJm+HxJMyxkV8pyydcK tUEYue2/FMLYbQH+tgptLvM3Oog== X-Received: by 2002:a05:620a:1116:: with SMTP id o22mr1055482qkk.263.1623366261643; Thu, 10 Jun 2021 16:04:21 -0700 (PDT) X-Google-Smtp-Source: ABdhPJwrG/yfGVS5sWgTKcNo1dgRgBZLWinZ0GsXIy0VHGuGgZrohA7iNbV+b0qys3C0GTOZDsvbFg== X-Received: by 2002:a05:620a:1116:: with SMTP id o22mr1055448qkk.263.1623366261403; Thu, 10 Jun 2021 16:04:21 -0700 (PDT) Received: from t490s (bras-base-toroon474qw-grc-88-174-93-75-200.dsl.bell.ca. [174.93.75.200]) by smtp.gmail.com with ESMTPSA id j14sm3076434qtj.96.2021.06.10.16.04.19 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 10 Jun 2021 16:04:20 -0700 (PDT) Date: Thu, 10 Jun 2021 19:04:19 -0400 From: Peter Xu To: Alistair Popple Message-ID: References: <20210607075855.5084-1-apopple@nvidia.com> <2773835.D95cIkl9rl@nvdebian> <6429491.QiJgnDeYu7@nvdebian> MIME-Version: 1.0 In-Reply-To: <6429491.QiJgnDeYu7@nvdebian> Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=peterx@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Disposition: inline X-Mailman-Approved-At: Sun, 27 Jun 2021 03:34:44 +0000 Subject: Re: [Nouveau] [PATCH v10 07/10] mm: Device exclusive memory access X-BeenThere: nouveau@lists.freedesktop.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Nouveau development list List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: rcampbell@nvidia.com, willy@infradead.org, linux-doc@vger.kernel.org, nouveau@lists.freedesktop.org, hughd@google.com, linux-kernel@vger.kernel.org, dri-devel@lists.freedesktop.org, hch@infradead.org, linux-mm@kvack.org, shakeelb@google.com, bskeggs@redhat.com, jgg@nvidia.com, akpm@linux-foundation.org, Christoph Hellwig Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Errors-To: nouveau-bounces@lists.freedesktop.org Sender: "Nouveau" On Fri, Jun 11, 2021 at 12:21:26AM +1000, Alistair Popple wrote: > > Hmm, the thing is.. to me FOLL_SPLIT_PMD should have similar effect to explicit > > call split_huge_pmd_address(), afaict. Since both of them use __split_huge_pmd() > > internally which will generate that unwanted CLEAR notify. > > Agree that gup calls __split_huge_pmd() via split_huge_pmd_address() > which will always CLEAR. However gup only calls split_huge_pmd_address() if it > finds a thp pmd. In follow_pmd_mask() we have: > > if (likely(!pmd_trans_huge(pmdval))) > return follow_page_pte(vma, address, pmd, flags, &ctx->pgmap); > > So I don't think we have a problem here. Sorry I didn't follow here.. We do FOLL_SPLIT_PMD after this check, right? I mean, if it's a thp for the current mm, afaict pmd_trans_huge() should return true above, so we'll skip follow_page_pte(); then we'll check FOLL_SPLIT_PMD and do the split, then the CLEAR notify. Hmm.. Did I miss something? -- Peter Xu _______________________________________________ Nouveau mailing list Nouveau@lists.freedesktop.org https://lists.freedesktop.org/mailman/listinfo/nouveau 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=-3.6 required=3.0 tests=BAYES_00,DKIM_INVALID, DKIM_SIGNED,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS 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 5BE79C48BE0 for ; Thu, 10 Jun 2021 23:04:28 +0000 (UTC) Received: from gabe.freedesktop.org (gabe.freedesktop.org [131.252.210.177]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 2CC11613E1 for ; Thu, 10 Jun 2021 23:04:28 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 2CC11613E1 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=dri-devel-bounces@lists.freedesktop.org Received: from gabe.freedesktop.org (localhost [127.0.0.1]) by gabe.freedesktop.org (Postfix) with ESMTP id A67436EE11; Thu, 10 Jun 2021 23:04:27 +0000 (UTC) Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [216.205.24.124]) by gabe.freedesktop.org (Postfix) with ESMTPS id A9FBB6EE11 for ; Thu, 10 Jun 2021 23:04:26 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1623366265; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=Kn4921Fy2QxClPboKoVBlarBT42fXZONHXvZsMc4G14=; b=CfKlhAmZb3hVqq2jr2l5kLw8iuG7uJZEXSceX1xRdpFnC6UbN6MJpQRV0LKpg/AoNsX9le 2aEsoJ2ldMY4KlinHnjh/wlk7yey2nY0z19TOhnJ94PKcaQRWMd0dvL9iO/NnfWomoMiT4 Z6/WJDQPPWtLgtdQ3J8OMbzchmbBhJk= Received: from mail-qv1-f72.google.com (mail-qv1-f72.google.com [209.85.219.72]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-191-YHdLE4IhPjGdSidku4Mi5A-1; Thu, 10 Jun 2021 19:04:22 -0400 X-MC-Unique: YHdLE4IhPjGdSidku4Mi5A-1 Received: by mail-qv1-f72.google.com with SMTP id t7-20020ad45bc70000b029023930e98a57so6238579qvt.18 for ; Thu, 10 Jun 2021 16:04:22 -0700 (PDT) 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=Kn4921Fy2QxClPboKoVBlarBT42fXZONHXvZsMc4G14=; b=Xd8/gpO5iA6FCHhGb1f3RwYTA7ls6R0dG2ClGKoQ+Pdnzv4Ve2EHVs534CArEQX9Bv xUQeRDQ8uaD6TK9O/COUP0SkLaf2HToNOKqrqSbErg5vrmUDexMnJVSgVwIr4rMfzDV1 nreLbNvrt1+1k1sB4VezgTCPbYcp+MEL2HETC1Ye8ifOW8Hppzl9wPRWllrzYcrZMZjn 7nlYpad7R7S2ZdWdPRybJnHAoLFk0z15WsD9wswrmWRm/Q/oimOD1qpDTh5trN2DjgZ3 VE1B8P3s1YA3OLIl+rfozsWLJpIGIco03jx9uHvZz0en2XPjIcuj0ujwZjse3S0E96Tb /Gsg== X-Gm-Message-State: AOAM530bueGWvx631KAwUZOPJ2A9cR+cf8V7rXVoR7s76xNDGPAisD+J 0gjCsgsn8iTBUfEXErYuwLhWc+duS6kJScI4IjRLUHiVbAndaD4lbrDk+VqZzCuYAg3tEmrhPKz nrB4YOGnIdDuXymlmWnNvbbBCPqrH X-Received: by 2002:a05:620a:1116:: with SMTP id o22mr1055468qkk.263.1623366261642; Thu, 10 Jun 2021 16:04:21 -0700 (PDT) X-Google-Smtp-Source: ABdhPJwrG/yfGVS5sWgTKcNo1dgRgBZLWinZ0GsXIy0VHGuGgZrohA7iNbV+b0qys3C0GTOZDsvbFg== X-Received: by 2002:a05:620a:1116:: with SMTP id o22mr1055448qkk.263.1623366261403; Thu, 10 Jun 2021 16:04:21 -0700 (PDT) Received: from t490s (bras-base-toroon474qw-grc-88-174-93-75-200.dsl.bell.ca. [174.93.75.200]) by smtp.gmail.com with ESMTPSA id j14sm3076434qtj.96.2021.06.10.16.04.19 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 10 Jun 2021 16:04:20 -0700 (PDT) Date: Thu, 10 Jun 2021 19:04:19 -0400 From: Peter Xu To: Alistair Popple Subject: Re: [PATCH v10 07/10] mm: Device exclusive memory access Message-ID: References: <20210607075855.5084-1-apopple@nvidia.com> <2773835.D95cIkl9rl@nvdebian> <6429491.QiJgnDeYu7@nvdebian> MIME-Version: 1.0 In-Reply-To: <6429491.QiJgnDeYu7@nvdebian> Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=peterx@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 Content-Disposition: inline X-BeenThere: dri-devel@lists.freedesktop.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Direct Rendering Infrastructure - Development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: rcampbell@nvidia.com, willy@infradead.org, linux-doc@vger.kernel.org, nouveau@lists.freedesktop.org, hughd@google.com, linux-kernel@vger.kernel.org, dri-devel@lists.freedesktop.org, hch@infradead.org, linux-mm@kvack.org, shakeelb@google.com, bskeggs@redhat.com, jgg@nvidia.com, jhubbard@nvidia.com, akpm@linux-foundation.org, Christoph Hellwig Errors-To: dri-devel-bounces@lists.freedesktop.org Sender: "dri-devel" On Fri, Jun 11, 2021 at 12:21:26AM +1000, Alistair Popple wrote: > > Hmm, the thing is.. to me FOLL_SPLIT_PMD should have similar effect to explicit > > call split_huge_pmd_address(), afaict. Since both of them use __split_huge_pmd() > > internally which will generate that unwanted CLEAR notify. > > Agree that gup calls __split_huge_pmd() via split_huge_pmd_address() > which will always CLEAR. However gup only calls split_huge_pmd_address() if it > finds a thp pmd. In follow_pmd_mask() we have: > > if (likely(!pmd_trans_huge(pmdval))) > return follow_page_pte(vma, address, pmd, flags, &ctx->pgmap); > > So I don't think we have a problem here. Sorry I didn't follow here.. We do FOLL_SPLIT_PMD after this check, right? I mean, if it's a thp for the current mm, afaict pmd_trans_huge() should return true above, so we'll skip follow_page_pte(); then we'll check FOLL_SPLIT_PMD and do the split, then the CLEAR notify. Hmm.. Did I miss something? -- Peter Xu