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=-0.9 required=3.0 tests=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 99F26C32771 for ; Wed, 15 Jan 2020 23:09:16 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 6B51E22522 for ; Wed, 15 Jan 2020 23:09:16 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="jBPUrvCj" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1731076AbgAOXJP (ORCPT ); Wed, 15 Jan 2020 18:09:15 -0500 Received: from us-smtp-delivery-1.mimecast.com ([207.211.31.120]:20181 "EHLO us-smtp-1.mimecast.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1730222AbgAOXJO (ORCPT ); Wed, 15 Jan 2020 18:09:14 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1579129753; 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: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=3kh6FESOjeCOQkkcKQDJe6CbgaZZXbwDLWZRH4+4Tss=; b=jBPUrvCj6p74elJ9vq+GP0zxVTTcZ9leECjxcqqL2tX7OkTPoq4zzwG0r8kG6c4eZ3Rqv1 fb4mYuEVgR321M9A7YHgh1VxHGYt8dkAd0XhRXq1Qbtn4A8fAqEAtP31ot/0jfriJXqhay YtEMBVg7J8h3Nqq8wA0oKPUuxSdGm2g= 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-185-UC9E83_LNMupIBVLbIZ7aA-1; Wed, 15 Jan 2020 18:09:09 -0500 X-MC-Unique: UC9E83_LNMupIBVLbIZ7aA-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 18964800D41; Wed, 15 Jan 2020 23:09:07 +0000 (UTC) Received: from warthog.procyon.org.uk (ovpn-120-52.rdu2.redhat.com [10.10.120.52]) by smtp.corp.redhat.com (Postfix) with ESMTP id 4EFA35D9C9; Wed, 15 Jan 2020 23:09:04 +0000 (UTC) Organization: Red Hat UK Ltd. Registered Address: Red Hat UK Ltd, Amberley Place, 107-111 Peascod Street, Windsor, Berkshire, SI4 1TE, United Kingdom. Registered in England and Wales under Company Registration No. 3798903 From: David Howells In-Reply-To: <7233E240-8EE5-4CD1-B8A4-A90925F51A1B@dilger.ca> References: <7233E240-8EE5-4CD1-B8A4-A90925F51A1B@dilger.ca> <4467.1579020509@warthog.procyon.org.uk> <00fc7691-77d5-5947-5493-5c97f262da81@gmx.com> <27181AE2-C63F-4932-A022-8B0563C72539@dilger.ca> <20200115133101.GA28583@lst.de> <23762.1579121702@warthog.procyon.org.uk> To: Andreas Dilger Cc: dhowells@redhat.com, Christoph Hellwig , Qu Wenruo , linux-fsdevel , Al Viro , "Theodore Y. Ts'o" , "Darrick J. Wong" , Chris Mason , Josef Bacik , David Sterba , linux-ext4 , linux-xfs , linux-btrfs , Linux Kernel Mailing List Subject: Re: Problems with determining data presence by examining extents? MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-ID: <7025.1579129743.1@warthog.procyon.org.uk> Content-Transfer-Encoding: quoted-printable Date: Wed, 15 Jan 2020 23:09:03 +0000 Message-ID: <7026.1579129743@warthog.procyon.org.uk> X-Scanned-By: MIMEDefang 2.79 on 10.5.11.14 Sender: linux-btrfs-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-btrfs@vger.kernel.org Andreas Dilger wrote: > > It would also have to say that blocks of zeros shouldn't be optimised = away. > = > I don't necessarily see that as a requirement, so long as the filesystem > stores a "block" at that offset, but it could dedupe all zero-filled blo= cks > to the same "zero block". That still allows saving storage space, while > keeping the semantics of "this block was written into the file" rather t= han > "there is a hole at this offset". Yeah, that's more what I was thinking of. Provided I can find out that something is present, it should be fine. David