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=-6.8 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 F142AC4363D for ; Tue, 22 Sep 2020 18:44:17 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id AC77320756 for ; Tue, 22 Sep 2020 18:44:17 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="P9tMI7aE" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726710AbgIVSoQ (ORCPT ); Tue, 22 Sep 2020 14:44:16 -0400 Received: from us-smtp-delivery-124.mimecast.com ([216.205.24.124]:54233 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726573AbgIVSoQ (ORCPT ); Tue, 22 Sep 2020 14:44:16 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1600800254; 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=j6MP6GjsyhJTZoS+wvVeQLSanb3L9bd67goL6s8H9bY=; b=P9tMI7aEifqUn64FnpsBK/nD5Zou6G7WAa6Yzemi3NQI4XW3EooQL4s8CPdFp6hfUXZYKR TDosnR0qTxiavNgHRb0MfzbnhijB3/PqxEc+ysA3MaQfvmfAPYcNhpuzEGkHlGpBAc/VR4 QiX4Nnw1o3k93jnmE8GMqHALGO/tXlk= 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-273-rEpsucqAN32nwnaZAUjGxQ-1; Tue, 22 Sep 2020 14:44:11 -0400 X-MC-Unique: rEpsucqAN32nwnaZAUjGxQ-1 Received: from smtp.corp.redhat.com (int-mx08.intmail.prod.int.phx2.redhat.com [10.5.11.23]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 12DAC8030A6; Tue, 22 Sep 2020 18:44:09 +0000 (UTC) Received: from dhcp-27-174.brq.redhat.com (unknown [10.40.192.146]) by smtp.corp.redhat.com (Postfix) with SMTP id CC09B1A800; Tue, 22 Sep 2020 18:44:01 +0000 (UTC) Received: by dhcp-27-174.brq.redhat.com (nbSMTP-1.00) for uid 1000 oleg@redhat.com; Tue, 22 Sep 2020 20:44:08 +0200 (CEST) Date: Tue, 22 Sep 2020 20:44:00 +0200 From: Oleg Nesterov To: Peter Xu Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, Linus Torvalds , Michal Hocko , Kirill Shutemov , Jann Horn , Kirill Tkhai , Hugh Dickins , Leon Romanovsky , Jan Kara , John Hubbard , Christoph Hellwig , Andrew Morton , Jason Gunthorpe , Andrea Arcangeli Subject: Re: [PATCH 4/5] mm: Do early cow for pinned pages during fork() for ptes Message-ID: <20200922184359.GI11679@redhat.com> References: <20200921211744.24758-1-peterx@redhat.com> <20200921212028.25184-1-peterx@redhat.com> <20200922114839.GC11679@redhat.com> <20200922124013.GD11679@redhat.com> <20200922155842.GG19098@xz-x1> <20200922165216.GF11679@redhat.com> <20200922183438.GL19098@xz-x1> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200922183438.GL19098@xz-x1> User-Agent: Mutt/1.5.24 (2015-08-30) X-Scanned-By: MIMEDefang 2.84 on 10.5.11.23 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 09/22, Peter Xu wrote: > > Or I can also do it in inverted order if you think better: > > if (unlikely(copy_ret == COPY_MM_BREAK_COW)) { > WARN_ON_ONCE(!data.cow_new_page); > ... > } Peter, let me say this again. I don't understand this code enough, you can safely ignore me ;) However. Personally I strongly prefer the above. Personally I really dislike this part of 4/5: again: + /* We don't reset this for COPY_MM_BREAK_COW */ + memset(&data, 0, sizeof(data)); + +again_break_cow: If we rely on "copy_ret == COPY_MM_BREAK_COW" we can unify "again" and "again_break_cow", we don't need to clear ->cow_new_page, this makes the logic more understandable. To me at least ;) Oleg.