Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751793AbbEZVgz (ORCPT ); Tue, 26 May 2015 17:36:55 -0400 Received: from mx1.redhat.com ([209.132.183.28]:50175 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750939AbbEZVgv (ORCPT ); Tue, 26 May 2015 17:36:51 -0400 Message-ID: <5564E76D.7080901@redhat.com> Date: Tue, 26 May 2015 17:36:45 -0400 From: Rik van Riel User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.4.0 MIME-Version: 1.0 To: Daniel Phillips , Jan Kara CC: David Lang , tux3@tux3.org, linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, OGAWA Hirofumi Subject: Re: [FYI] tux3: Core changes References: <555D0FDF.3070303@phunq.net> <555D500B.4080901@phunq.net> <13c8bcdf-70e8-43d5-a05f-58ad839dbfd0@phunq.net> <5563F5C8.2040806@redhat.com> <67294911-1776-46b8-916d-0e5642a38725@phunq.net> <20150526070910.GA3307@quack.suse.cz> <20150526090058.GA8024@quack.suse.cz> <5564D60E.6000306@phunq.net> In-Reply-To: <5564D60E.6000306@phunq.net> Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1280 Lines: 30 On 05/26/2015 04:22 PM, Daniel Phillips wrote: > On 05/26/2015 02:00 AM, Jan Kara wrote: >> So my opinion is: Don't fork the page if page_count is elevated. You can >> just wait for the IO if you need stable pages in that case. It's slow but >> it's safe and it should be pretty rare. Is there any problem with that? > > That would be our fallback if anybody discovers a specific case where page > fork breaks something, which so far has not been demonstrated. > > With a known fallback, it is hard to see why we should delay merging over > that. Perfection has never been a requirement for merging filesystems. On However, avoiding data corruption by erring on the side of safety is a pretty basic requirement. > the contrary, imperfection is a reason for merging, so that the many > eyeballs effect may prove its value. If you skip the page fork when there is an elevated page count, tux3 should be safe (at least from that aspect). Only do the COW when there is no "strange" use of the page going on. -- All rights reversed -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/