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=-3.9 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 A14ECC433E7 for ; Mon, 19 Oct 2020 16:55:09 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 3A56922277 for ; Mon, 19 Oct 2020 16:55:09 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="Tn3XeBj4" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730687AbgJSQzI (ORCPT ); Mon, 19 Oct 2020 12:55:08 -0400 Received: from us-smtp-delivery-124.mimecast.com ([63.128.21.124]:53234 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1730322AbgJSQzH (ORCPT ); Mon, 19 Oct 2020 12:55:07 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1603126506; 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=UIbgrH9eig0psNy0ASBb0vz+iWA/QXOrTGiB/ABhnmc=; b=Tn3XeBj48RlYwnXcVL9tZwVpIMS4XIi3IJ+Zp6uKNxPqouvVHdaMAa3VbU/CtF1FyodN07 /Xlt3C0oOSCjLXT4RWtbuenlpMRZ4mHFdKkr+KLikNg11xgyqxS2VkPJ9n069vJ3UZaZBo eaJqgbAPckPAjuFQSXuJEVqS3CLfoHs= 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-408-9iXIkeU7Pd6nvSlKqryVmg-1; Mon, 19 Oct 2020 12:55:04 -0400 X-MC-Unique: 9iXIkeU7Pd6nvSlKqryVmg-1 Received: from smtp.corp.redhat.com (int-mx04.intmail.prod.int.phx2.redhat.com [10.5.11.14]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 7AF5A425CF; Mon, 19 Oct 2020 16:55:03 +0000 (UTC) Received: from bfoster (ovpn-112-249.rdu2.redhat.com [10.10.112.249]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 08C8C5D9D2; Mon, 19 Oct 2020 16:55:02 +0000 (UTC) Date: Mon, 19 Oct 2020 12:55:01 -0400 From: Brian Foster To: Christoph Hellwig Cc: linux-fsdevel@vger.kernel.org, linux-xfs@vger.kernel.org Subject: Re: [PATCH 1/2] iomap: use page dirty state to seek data over unwritten extents Message-ID: <20201019165501.GA1232435@bfoster> References: <20201012140350.950064-1-bfoster@redhat.com> <20201012140350.950064-2-bfoster@redhat.com> <20201015094700.GB21420@infradead.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20201015094700.GB21420@infradead.org> X-Scanned-By: MIMEDefang 2.79 on 10.5.11.14 Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org On Thu, Oct 15, 2020 at 10:47:00AM +0100, Christoph Hellwig wrote: > I don't think we can solve this properly. Due to the racyness we can > always err one side. The beauty of treating all the uptodate pages > as present data is that we err on the safe side, as applications > expect holes to never have data, while "data" could always be zeroed. > I don't think that's quite accurate. Nothing prevents a dirty page from being written back and reclaimed between acquiring the (unwritten) mapping and doing the pagecache scan, so it's possible to present valid data (written to the kernel prior to a seek) as a hole with the current code. Brian