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=-7.5 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,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 0BC53C433E0 for ; Thu, 7 Jan 2021 22:04:49 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id B20792343B for ; Thu, 7 Jan 2021 22:04:48 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727699AbhAGWEc (ORCPT ); Thu, 7 Jan 2021 17:04:32 -0500 Received: from us-smtp-delivery-124.mimecast.com ([216.205.24.124]:27148 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726477AbhAGWEb (ORCPT ); Thu, 7 Jan 2021 17:04:31 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1610056985; 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=JrnpLFfBtiXLpDV0Rk0B5DNVndwdwJuqAhmGaVVEq5M=; b=SC5JuOcPWBLKD10fx0XZnpjUcJ2KJaWr/GDS2iEHPC6lzeRPnVX1F7r3G1hpShDKnq7TMf xWNRT61n/7uZ7wftoAfxl7W0ewbWNV2rvoBqKj8ZBFdpoZ4mZ8fxv/PxEU9LOMJzNqGKkz W2nKK3eLbBWMHch2a9Hy6DfyxkFUgjg= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-233-KF08uPqtPfmCwAVyIqqE-g-1; Thu, 07 Jan 2021 17:03:01 -0500 X-MC-Unique: KF08uPqtPfmCwAVyIqqE-g-1 Received: from smtp.corp.redhat.com (int-mx03.intmail.prod.int.phx2.redhat.com [10.5.11.13]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id A57351842140; Thu, 7 Jan 2021 22:02:57 +0000 (UTC) Received: from mail (ovpn-112-222.rdu2.redhat.com [10.10.112.222]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 74BCB6090F; Thu, 7 Jan 2021 22:02:51 +0000 (UTC) Date: Thu, 7 Jan 2021 17:02:50 -0500 From: Andrea Arcangeli To: Linus Torvalds Cc: Jason Gunthorpe , Linux-MM , Linux Kernel Mailing List , Yu Zhao , Andy Lutomirski , Peter Xu , Pavel Emelyanov , Mike Kravetz , Mike Rapoport , Minchan Kim , Will Deacon , Peter Zijlstra , Hugh Dickins , "Kirill A. Shutemov" , Matthew Wilcox , Oleg Nesterov , Jann Horn , Kees Cook , John Hubbard , Leon Romanovsky , Jan Kara , Kirill Tkhai Subject: Re: [PATCH 0/2] page_count can't be used to decide when wp_page_copy Message-ID: References: <20210107200402.31095-1-aarcange@redhat.com> <20210107202525.GD504133@ziepe.ca> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/2.0.4 (2020-12-30) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.13 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Jan 07, 2021 at 01:05:19PM -0800, Linus Torvalds wrote: > I think those would very much be worth fixing, so that if > UFFDIO_WRITEPROTECT taking the mmapo_sem for writing causes problems, > we can _fix_ those problems. > > But I think it's entirely wrong to treat UFFDIO_WRITEPROTECT as > specially as Andrea seems to want to treat it. Particularly with > absolutely zero use cases to back it up. Again for the record: there's nothing at all special in UFFDIO_WRITEPROTECT in this respect. If you could stop mentioning UFFDIO_WRITEPROTECT and only focus on softdirty/clear_refs, maybe you wouldn't think my judgment is biased towards clear_refs/softdirty too. You can imagine the side effects of page_count doing a COW erroneously, as corollary of the fact that KSM won't ever allow to merge two pages if one of them is under GUP pin. Why is that? Thanks, Andrea