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=-5.2 required=3.0 tests=BAYES_00, 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 A6AA2C4361B for ; Mon, 7 Dec 2020 14:58:41 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 7732D23601 for ; Mon, 7 Dec 2020 14:58:41 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727089AbgLGO6U (ORCPT ); Mon, 7 Dec 2020 09:58:20 -0500 Received: from mx2.suse.de ([195.135.220.15]:51078 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725772AbgLGO6U (ORCPT ); Mon, 7 Dec 2020 09:58:20 -0500 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.221.27]) by mx2.suse.de (Postfix) with ESMTP id DC3ABAC2E; Mon, 7 Dec 2020 14:57:38 +0000 (UTC) Received: by ds.suse.cz (Postfix, from userid 10065) id C37ACDA7BA; Mon, 7 Dec 2020 15:56:03 +0100 (CET) Date: Mon, 7 Dec 2020 15:56:03 +0100 From: David Sterba To: Qu Wenruo Cc: linux-btrfs@vger.kernel.org, linux-fsdevel@vger.kernel.org Subject: Re: [PATCH RFC] btrfs: remove cow fixup related code Message-ID: <20201207145603.GA6430@twin.jikos.cz> Reply-To: dsterba@suse.cz Mail-Followup-To: dsterba@suse.cz, Qu Wenruo , linux-btrfs@vger.kernel.org, linux-fsdevel@vger.kernel.org References: <20201207071352.106160-1-wqu@suse.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20201207071352.106160-1-wqu@suse.com> User-Agent: Mutt/1.5.23.1-rc1 (2014-03-12) Precedence: bulk List-ID: X-Mailing-List: linux-btrfs@vger.kernel.org On Mon, Dec 07, 2020 at 03:13:52PM +0800, Qu Wenruo wrote: > >From the initial merge of btrfs, there is always the mystery cow fixup. For the record, the code needs to stay for because it's still needed. Though finding the exact point where it happens on intel architectures is not easy, it's required on s390 because of the separate page bits tracking at least. How exactly it works and why the code exists is left as an exercise to the reader.